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OKRIGHT DEPOSm 



MANUAL 



OF 



Plant Diseases 



BY 



PROF. DR. PAUL SORAUER 



Third Edition — Prof. Dr. Sorauer 

In Collaboration with 

Prof. Dr. G. Lindau And Dr. L. Reh 

Private Docent at the University Assistant in the Museum of Natural 

of Berlin History in Hamburg 



TRANSLATED BY FRANCES DORRANCE 



MANUAL 



OF 



Plant Diseases 



BY 



PROF. DR. PAUL SORAUER 



Third Edition— Prof . Dr. Sorauer 

In Collaboration with 

Prof. Dr. G. Lindau And Dr. L. Reh 

Private Decent at the University Assistant in the Museum of Natural 

of Berlin - History in Hamburg 



TRANSLATED BY FRANCES DORRANCE 



Volume I 
NON-PARASITIC DISEASES 

BY 

PROF. DR. PAUL SORAUER 

BERLIN 



WITH 208 ILLUSTRATIONS IN THE TEXT 



^v 



n'?>^ 



Copyrighted, 1922 

By 

FRANCES DORRANCE 



. 



g)S!.A6o9795 



S)^ 



ERRATA. 

Contents, page X, line 2t,, for Leguminaceae, read Leguniinosae. 
Page 8, line 23, for stems, read shoots. 

23, " 16, " preventive, read preventative. 
53, " 5, " Prunualus, read Prunulus. 
93, Fig. 4, caption, for Schomiinzach, read Schonmiinzach. 
99, line 34, for Mvcor spinosa, read Mucor spinosus. 
167, " 22, " Arahanose, read Arabinose. 
204, " 37, " Fusiarium, read Fusarium. 
232, " 5, " Leguminoseae, read Leguniinosae. 

" 21, " Dioscora, read Dioscorea. 
265, " 19, " Zolites, read Zeolites. 
^73' " 6, *' B. suhstilis, read B. sttbtilis. 

" 7-8, " Clostridium gelatinosa, read Clostrid'mm gelatinosum. 
" 18, after Mold fungi, insert (Mucor stolonifcra and Asper- 
gillis niger). 
293, " 20, for homogany, read homogamy. 

338, " 30, " fruit spears, read fruit spurs. 

339, " II, " Fruchtuchen, read Fruchtkuchen. 
420-22 " Leguminaceae, read Leguniinosae. 
430, line II, after inner growth, insert (internal intumescences). 
442, Fig. 80, caption, for Acacia pendulata, read Acacia pendida. 
461, line 24, after rough places, insert (scurvy spots). 
498, " I, for Chapter XL, read Chapter XL 
548, " 24, " psycho-clinic, read psychroTclinic. 
696, " 22, " Bacillus pseudarabinus, read Bact. pseudarahinum. 
723, " 38, " Grapholithia, read Grapholitha. 
765, " 36, " Boulle celeste, read Bouillie celeste. 
802, Fig. 186, caption, for forniaton, read formation. 
855, line II, for Trula, read Torula. 

" II, " vernatis, read vernalis. 



Vll 



TABLE OF CONTENTS. 



Page 
PREFACE to the German edition 3 

IXTRODUCTIOX. 

Section I. THE NATURE OF DISEASE. 

1. Limitation of the conception of disease 5 

2. Production of the disease 8 

3. Relation of the plant to its environment ro 

4. Parasitic diseases ^3 

5. Epidemics ^9 

6. Artificial immunization and internal therapy 23 

7. Predisposition ^5 

8. Predisposition and immunity 27 

g. Inheritance of disease and of predisposition 3i 

10. Degeneration 34 

Section 2. HISTORICAL SURVEY. 
Historical Survey 4i^"70 

APPENDIX 70 

DETAILED EXPOSITION. 

Section I. DISEASES DUE TO UNFAVORABLE SOIL CONDITIONS. 
Chapter I. The location of the soil 72 

1. Elevation ahove sea level T^ 

a. General changes in habitat. 

In relation to herbaceous plants 1^ 

Development of the aerial axis of woody plants 76 

Adjustment of the root body of woody plants 78 

b. Special cases of disease 81 

Retrogression in the cultivation of the larch 81 

Lack of success with tropical plantations 84 

2. Slope of the surface of the soil 86 

a. Too steep slopes 89 

b. Growth of stilts, elevation of the roots of trees 92 

c. Too deep planting 9° 

Too deep planting of trees 98 

Too deep sowing of seed ^^ 

Roots from the tips of grain seeds Ho 

3. Greater horizontal differences ^-O 

Glassy grain kernels ^^9 

4. Continental and marine climates ^31 

5. Influence of forests ^34 

Chapter II. Unfavorable physical constitution of the soil T38 

1. Limited soil mass ^38 

Root curvature ^^ 

Dwarf growth ( Nanism ) ^■^- 

Too thick seeding ^47 

2. Unsuitable soil structure ^4o 

a. Light soils ^4« 

Disadvantage of sandy soils ^4o 

Lowering of the ground water level '50 

The dying of alders ^^3 

Street planting ^53 

Effect of drought on field products ^55 

Effect of drought on germination ^57 

Treatment of tree seeds ^5° 

Blasting in grains and legumes i"" 



Vlll 

Page 

Thread formation in the potato (Filositas) i6i 

Diaphysis (Growing out) of the potato 163 

Formation of tubers without foliage 164 

Aerial potato tubers 165 

Premature ripening of fruits 165 

Rusty plums . ._ 166 

Further phenomena of premature ripening 166 

Mealiness of fruit 166 

Bitter pit in the apple 168 

Stoniness of pears and lithiasis 170 

Varieties of fruit suitable for dry soils 174 

Stunting of plants 175 

Pilosis 177 

Lignification of roots 179 

Ball dryness of the Ericaceae 181 

Means of overcoming lack of moisture in the soil 182 

Irrigation 182 

Cultivation of the soil 183 

Mulching of the soil 184 

Soils with a plant cover 185 

Forest litter 186 

Forests 187 

Fallow land 188 

b. Loamy soils 189 

General characteristics 189 

Covering of the soil with silt 191 

Improvement of soils which are becoming compact 194 

Inundations 195 

Conversion of lands into swamps 196 

Burning of plants in moist soils 199 

Delayed seeding 200 

Souring of seed 201 

Souring of potted plants 203 

Injudicious watering 206 

' Use of saucers under pots 208 

Running out of potatoes 208 

Sensitiveness of the sweet cherry 209 

Tan disease 209 

Girdling of the red beech 219 

Root disease of the true chestnut (Mai nero) 219 

Rootblight of sugar and fodder beets 220 

Tropical plants 227 

■ Root-rot of sugar cane 227 

i ■ Diseases of cotton 228 

Castor bean cultures 229 

Tobacco 229 

Cofifee 230 

Cocoa and tea 231 

Other tropical plants 231 

Means for overcoming the disadvantages of heavy soils 232 

Harrowing 236 

Use of lime, marl, and plaster 237 

3. Disadvantages of moor soil 240 

Acids in the soil 240 

Raw humus 241 

Meadow ore 243 

Poisoning of the soil by metallic sulfur 250 

Susceptibility to frost of moor vegetation 251 

The usefulness of the spruce 253 

Changes in moor soil through cultivation 256 

Rotten bark 258 

Horticultural moor plants 260 

Specking of orchids 261 

Chapter III. Unfavorable chemical soil constitution 264 

r. Relation of the food stufifs to the soil structure 264 

A. Soil absorption resulting from chemico-physical processes 264 

B. Work of the soil organisms 268 



IX 

Page 
2. Relation of the nutritive substances to tlie plants 274 

A. Lack of moisture and nutritive substances 27s 

a. Lack of moisture i 275 

Influence of the various plant coverings 275 

Wilting 276 

Change in production due to lack of moisture 278 

Discoloration of woody plants 279 

Red coloration in grain 281 

"Reds" of hops 282 

"Leaf scorch" of grapes, "Parching" of vines, "Red scorch" 283 

Yellowing due to the grafting stock 284 

Premature drying of the foliage 284 

Burning out of grass 285 

Silver leaf 285 

Water core of apples -. 286 

b. Changes in production due to a lack of nitrogen 287 

Starvation conditions in Cryptogams 287 

Production of sterile blossoms ( Sterility ) 289 

Seedless fruits 292 

Behavior of weak seeds 295 

Dropping of the fruit 296 

Drying of the inflorescences on decorative plants 296 

Formation of thorns 297 

c. Changes in production due to a lack of potassium 298 

d. Changes in production due to a lack of calcium 301 

e. Changes due to a lack of magnesium 305 

f. Changes due to a lack of chlorin 306 

g. Lack of iron and "jaundice" (Icterus ) 307 

h. Changes due to a lack of phosphorus and sulphur 312 

i. Changes due to a lack of oxygen 313 

General phenomena 313 

Brusone disease of rice 31S 

Diseases of gladioli 316 

k. Changes due to a lack of carbon-dioxid 316 

B. Excess of water and nutritive substances 319 

a. Excess of water 319 

Moisture 319 

Clogging of drain tiles 319 

Sprouted grain 320 

Rupturing of fleshy parts of plants 321 

Woolly streaks in apple cores 324 

Ring disease of hyacinth bulbs 326 

Springing of the bark Z^~ 

Shedding of the bark 328 

Water sprouts 331 

Union of parts Z2>Z 

Compulsory twisting (Spiralismus Mor.) 334 

Dropsy ( Oedema ) 335 

a. In small fruits 335 

b. In stone fruits 338 

Swellings on the St. John's Bread tree 339 

Retrogressive metamorphosis (Phyllody) 340 

Barrenness of the hop 342 

Forked growth of grape vines 34S 

Falling of the leaves 346 

Leaf casting diseases 349 

Leaf-fall in house plants 352 

Dropping of the flowering organs 353 

Shelling of the grape blossom 354 

Shedding of the young flower clusters of hyacintlis 356 

Twig abscission 357 

b. Increase of food concentration 360 

Changes in meadows 362 

Sewage disposal fields 364 

Scurvy disease 367 

Progressive metamorphosis 372 

Pressure of the buds (Blastomania A. Br.) 378 



X 

Page 
Goitre gnarl of trees 378 

c. Effect of an excess of nitrogen 387 

Over-fertilized seed 387 

Over-fertilized beets 389 

Over-fertilized potatoes 390 

Chile saltpetre with woody plants 391 

Over-fertilization of vegetables and other field crops 392 

Excessive nitrogen fertilization for decorative plants 393 

Leaf curl of the potato 395 

d. Excess of calcium and magnesium 399 

Excess of calcium with grapes 402 

e. Excess of potassium 403 

f. Excess of phosphoric acid 405 

g. Excess of carbon-dioxid 406 

Section 2. INJURIOUS ATMOSPHERIC INFLUENCES. 

Chapter IV. Too dry air 408 

Injury to buds 408 

Defoliation due to heat 411 

Honey dew 412 

Heart rot and dry rot of fodder and sugar beets 415 

Fault}' development of the blossoms 416 

House plants 419 

Hard seeds in the Leguminaceae 420 

Chapter V. Excessive humidity , 423 

Mode of growth with continued atmospheric humidity 423 

Influence of moist air on plants injured by drought 425 

Cork outgrowths 426 

Cork disease of the cacti 428 

Bitten or perforated leaves 430 

Formation of cork on fruits 432 

Yellow spots (Aurigo) 434 

Intumescences 435 

Tubercle disease of the rubber plant 449 

Skin diseases of hyacinths 451 

Glassy condition of cacti 453 

Chapter VI. Fog 458 

Chapter VII. Rainstorms 461 

Chapter VIII. Hail 463 

Chapter IX. Wind 471 

Chapter X. Electrical discharges 480 

Flashes of lightning 480 

Blight of conifer tops 487 

Differences between lightning and frost wounds in conifers 489 

Injuries to trees in cities and towns 493 

Effect of spray lightning on grapevines 493 

Spray lightning on fields and meadows 495 

Disadvantages in electro-culture 496 

Chapter XI. Lack of heat 498 

A. General survey 498 

Life phenomena at low temperatures 498 

Autumn coloration 500 

Frosting and freezing to death 504 

Theories as to the nature of frost action 507 

Disturbances due to chilling S13 

B. Special instances of frost action 514 

Turning sweet of potatoes 514 

Running to seed of beets 516 

Frosty taste in grapes 518 

Changes in the blossom organs 5^8 

Rust rings in fruits 523 



XI 

Page 

Behavior of older foliage with acute frost action 524 

Deficient greening of younger leaves [ ]] [526 

Defoliation due to frost 527 

Behavior of beet and cabbage plants in frost !!.'!! 531 

Frost blisters 53-? 

Comb-like splitting of the leaves [.[ , 53" 



Heaving of seeds 



536 



Internal injuries in young grain "507 

Internal injuries in the grain stalk g^g 

Lodging of the stalk 542 

Condition of sterile heads ] [ '542 

Phenomena of movement due to frost 547 

Freezing back of older branch tips ]] .553 

Dying of the cherry trees along the Rhine 555 

Branch blight in forest trees " I558 

Freezing of the spring growth \ '55P 

Freezing of roots '^62 

Frost clefts ' | "^55 

Frost blisters \ 'egg 

Frost wrinkles c-i 

Bark tatters and cork holes 575 

Phenomena of discoloration in trunks and branches 576 

Frost line ^jg 

Internal splitting of the trunk and branches 581 

Open frost tears ' ' ^g^ 

Canker ( Carcinoma) 585 

a. Canker of the apple tree 586 

b. Crotch canker in fruit and forest trees 593 

c. Canker on cherry trees ^g^ 

d. Canker (Scab) of the grapevine 596 

e. Canker on Spiraea 598 

f . Canker of the rose 602 

g. Canker of the blackberry 606 

Corresponding features in canker swellings 607 

Blight (Sphacelus) 608 

Aggregations of parenchyma wood 613 

False annual rings, double rings, etc 615 

Experimental production of parenchyma wood by frost action .".617 

Theory of the mechanical action of frost 620 

Rupture of the cuticle 623 

Protective measures against frost • 624 

a. Snow covering 624 

b. Use of water 626 

c. Effect of wind 627 

d. Smudge 628 

Frost prediction 630 

Hardy fruit varieties 631 

Snow pressure, ice coating and icicles 634 

Chapter XII. Excess of heat 638 

Death from heat 638 

Poor development of our vegetables in the tropics 639 

Postponement of the usual seed time in our latitudes 639 

Sunburn of leaves in nature 641 

Sunburn spots in conservatories 643 

Defoliation 6^ 

Sunburn in blossoms and fruits 645 

Injury to grapes from sunburn 646 

Sun cracks 647 

Influence of too great soil heat 648 

Failure of the pineapple 650 

Classiness of orchids 651 

Failure in forcing blossom bulbs 651 

Seed which has suffered from self-heating 652 

Chapter XIII. Lack of light 654 

Etiolation 654 

Shading .657 



Xll 

Page 

Lodging of grain 662 

Lack of light as predisposition to disease 666 

Chapter XIV. Excess of light 671 

Section 3. ENZYMATIC DISEASES. 

Chapter XV. Displacement of enzymatic functions 675 

General discussion 675 

Albinism (Variegation) 677 

Mosaic disease of tobacco 684 

Pox of tobacco 689 

White rust of tobacco 690 

Disease of the peanut in German East Africa 690 

Shrivelling disease of the mulberry 690 

Sereh disease of the sugar cane 692 

Cobb's disease of the sugar cane ^96 

Peach yellows 697 

Gummosis of the cherry 699 

Exudation of gum in other plants 707 

Exudation of gum in the Acacia 707 

Gummy exudation of the bitter orange 708 

Black-leg of the edible chestnut 709 

Gummosis of the 'fig tree 710 

Exudation of manna 711 

Resinosis 7 r i 

Formation of resin in dicotyledonous plants 716 

Section 4. EFFECT OF INJURIOUS GASES AND LIQUIDS. 

Chapter XVI. Gases in smoke 71S 

Sulphurous acids 718 

Hydrochloric acid and chlorin 724 

Hydrofluoric acid 729 

Nitric acid 730 

Ammonia 730 

Tar and asphalt fumes 732 

Bromine 735 

Chapter XVII. Solid substances given off by chimneys and the distillates they 

contain "jT)"/ 

Hydrogen sulfid 742 

Soda dust 743 

Control plants 744 

Illuminating gas and acetylene 744 

Chapter XVIII. Waste water 748 

Waste water containing sodium chlorid 748 

Waste water containing calcium chlorid and magnesium chlorid 751 

Waste water containing barium chlorid 752 

Waste water containing zinc sulfate 752 

Waste water containing iron sulfate 753 

Waste water containing copper sulfate and copper nitrate 754 

Chapter XIX. Injurious effects of cultural methods 756 

Coating substances 756 

Anaesthetica 765 

Injuries due to fertilizers 767 

Section 5. WOUNDS. 

Chapter XX. Wounds to the axial organs T/2 

General discussion 772 

Scarification wounds 776 

Inscriptions 781 

Injury due to wild animals 781 

Overgrowth of cross wounds in many-year-old trees 783 

Overgrowth processes in year-old branches 785 

Girdling callus 787 



Xlll 

Page 

Injuries to the bark 797 

Historical survey 797 

Personal observations 805 

Bending of the branches 810 

Twisting of the branches 815 

Effect of constricting the axis 817 

Branch cuttings 821 

Utilization of various axial organs for cuttings 825 

Grafting 829 

Oculation, or budding 833 

Copulation and grafting 838 

Longevity of grafted or budded individuals 839 

Mutual influence of scion and stock 841 

Natural processes of coalescence 847 

Wound protection 850 

Wound gum 851 

Slimy exudation of trees 854 

Root injuries 856 

Gnarly overgrowth edges 859 

Bark tubers .861 

Leaf injuries 871 

Leaf cuttings 873 

Injury to the foliage 879 

Supplement 881 



XIV 



LIST OF ILLUSTRATIONS. 



Fig. Page 

I, 2. Roots of Quercus Pedunculata grown between rocks 79 

3. Spruce root with fleshy compensatory root 81 

4. Stihed spruce near Schonmunzach 93 

5, 6- Stilted pine from Grunewald 95 

", 8. Resin galls on stilt-like roots of the pine 96 

9. Rye seedling with too deep sowing 112 

■ 10. Cross section through the lowest node of young rye plant 1 14 

II. Wheat -grains with roots from testa at tip of seed grain 116 

12, 13, 14. Microscopical enlargements of Fig. 11 117, 119 

15. Dwarf specimen of Thuja obhisa ^ 1-^3 

16. Cutting from potato tuber with the filament disease 162 

■ 17. Proliticated potato 163 

- 18. Parenchyma cell from ripe apple after treatment with undiluted glycerin 169 

■ 19. * Pear diseased with Lithiasis .171 

" 20. Cross-section of stone cell from pear snown in Fig. 19 173 

f.2ij 22. Corr-esponding sections through a cultivated and a wild carrot 181 

■ 23. Apple root with ruptured tan spots 210 

' 24. Cross-section through a tan spot in an apple root - 211 

25. Bark of apple tree trunk with tan spots 212 

26. Cross-section through tan spot on trunk of apple tree 213 

27. Cherry branch with tan cushions 214 

28. New wood on a bark wound of a cherry trunk 216 

29 A "meadow ore pine" 246 

30. Roots of an oak in meadow ore 247 

31. Moor pine with flatly extended roots 248 

^ 32. Canker-like, wounded place on the moor pine 249 

33. Spruce family produced by natural layering 254 

34. Oak with a formation of sinkers 255 

35. Mouldy bark scale of a moor pine 259 

36. Seedless pear 294 

\37- Cross-section through branch of Rhamnus cathartica 298 

^ 38. Cross-section through thorn of Rhamnus cathartica 299 

39. Leaf injuries from a lack of potassium 302 

40. Buckwheat plant grown in a normal nutrient solution 307 

41. Buckwheat plant grown in a solution free from chlorin 308 

42. Bean plant split as the result of excess of water 322 

43. Apple core with woolly streaks 324 

44. Rupture of carpel of apple due to a woolly streak 325 

45. Elm bark with protruding tissue islands 328 

46. Elm bark with bark excrescence (cross-section) 329 

47, 48. Fasciated branch of Picea excelsa 332 

49. Fasciation of Alnus glutinosa 333 

50. Dropsy in Ribes aiireuin 33^ 

51. Transitional stages between normal and leafy hop catkins 343 

52. Carrot diseased with deep scurvy 3^7 

53. Lentical formation on the potato skin 369 

54. Cone disease in the Scotch pine 373 

55. Sprouting pears 374 

56. Larch cone with growth of the axis continued 375 

57. Rosette shoot of a Scotch pine 377 

58. Peeled, gnarled growth of the maple 379 

59. Gnarl formation on branches of Mains sinensis 380 

60. Cross-section through a gnarl cushion 380 

61. Longitudinal section through the spikes of a gnarl 381 

62. Gnarl formation in the black currant 382 

63. Cross-section through twig covered with gnarls 383 

64. Cross-section through bark of the black currant 383 

65. Medullary ray in the first stages of gnarl formation . . • • ■ 384 

66. Diagrammatic representation of mutual relations of fertilizers 400 

•67, 68. Cross-sections through the bud coverings of Quercus and of Pinus 409 



XV 

Fig. Page 

69. Cross-section through the apical region of a closed blossom of Hippeastntiii 

robustutn 418 

70, 71. Cork excrescences in Phyllocactus 428, 429 

^2. Perforated potato leaf, due to cork formation 431 

y2- Grapes with cork warts on fruit stems 432 

74. Cross-section through the warty fruit stem of a grape 433 

75. Leaf intumescences in Cassia tomeiitosa 436 

76. Intumescence in Myrniecodia echinata 437 

//. Intumescence on the stem of a grape 439 

78. Intumescence on the lower node of an oat plant 441 

79. Intumescence on stem of Lavetera triincstris 442 

So, 81. Intumescence on branch of Acacia pciuiiila . .442 

82. Cross-section through intumescence of Acacia pendiila 443 

83. Intumescence on blossom of Cymbidimn Lozvi 444 

84. Cross-section through intumescence on perianth of Cymbidntm Lozvi 445 

85, 86. Intumescence on pea-pods 446, 447 

87. Cross-section through leaf tubercle of the rubber tree 450 

88, 89. Hyacinth bulb with pustules of the skin disease 451, 452 

90. Glassy place in Cereus nycticalus 456 

91. Effect of hail on a blade of rye 464 

92, 93. Head of wheat broken by hail 465, 466 

94. Cross-section through tomato wall, injured by hail 467 

95. Wind bent and broken spruces 473 

96. Craspedodromous and Camptodromous venation 478 

97. Oak, struck by lightning 482 

98. Cross-section through spruce with overgrown lightning wounds 484 

99. Cross-section through annual ring of a spruce, in year it was struck by 

lightning 485 

roo. Cross-section through a blighted spruce tip 487 

loi. Pine, artificially frosted 490 

102. Spruce, showing traces of artificial lightning 492 

103. Cross-section through petal of apple, injured by artificial frost 520 

104. Cross-section through young receptacle of apple injured by frost 521 

105. Primordia of apple flower bud, injured by frost 522 

106. Autumnal abscission layer of a horse chestnut leaf 528 

J07. Cross-section through a frost boil in an apple leaf 533 

108. Horse chestnut leaf, injured by frost and torn during unfolding 535 

log. Young rye leaf, injured by frost 538 

no. Natural cavities in the rye leaf 539 

III. Leaf node from a rye plant, injured by frost 540 

T12, 113. Membrane swellings on leaf sheaths of a rye blade, injured by frost 540 

114. Different forms of sterility 543 

115. Cross-section through internode of a sterile rye blade 544 

116. Cross-section through the node of the sterile stalk 545 

117. Cross-section through a spruce branch, showing red wood formation 551 

118. 119. Red wood and strain wood in the spruce 552 

120. Cherry sapling infected with J'alsa leucostoiiia 557 

121. Buds of the cherry, injured by artificial frost 560 

122. Frost ridge on the trunk of Acer caiiipesfre 567 

T23. Oak stem, cleft by Polyponis sulfureus 569 

124. Starch structures formed in the willow branch by chloriodid of zinc 

treatment 572 

125, 126. Frost boil on a sweet cherry branch 573, 574 

127. Torn cork lamellae on branch injured by frost 576 

128. Splitting of a pear branch by artificial frost 578 

129. Swelling of eel! walls after artificial frost 580 

T30. Interna] splitting of cherry branch from artificial frost 582 

13T. Bud cushion of a larch branch, injured by artificial frost 584 

T32. Overgrowing frost split in apple branch, produced by artificial frost 586 

'^32,^ 134, 135. Apple canker '. 587, 588 

136. Juvenile condition of apple canker 590 

137. Injury to base of branch by frost .S9i 

T38. Crotch canker 593 

T3Q. Cherry canker 595 

140. Canker excrescences in the grapevine 596 

141. Canker on Spiraea 599 

142. 143. Rose canker 602, 604 



XVI 

Fig. Page 

144. Canker of the wild blackberry 606 

145. Frost spots on pear bark 608 

146. 147. Blight spots on pear trunk 610, 611 

148', 149. Internal frost wounds on an oak branch 618, 621 

T50.' Curve for finding night frosts 631 

151. Cross-section through sunburn spot in leaf of Clivia nobilis 643 

152, 153, 154- Light and shade leaves of the beech 660 

155.' Twig of cherry with gum cavity 701 

156. Nuclei of gum-forming tissue 704 

157. Tracheidal parenchyma of Pinus Strobus with resiniferous layer 713 

158. 159, 160, 161. Resin centers in amber 714-716 

162. Oat leaf killed by chlorin fumes 726 

163. Beech leaf affected by sulf urous acid 727 

164. Birch leaves injured by sulf urous acid 728 

165. Rose leaf inj ured by chlorin fumes 728 

166. Beech leaves injured by chlorin fumes 728 

167. Birch leaves injured by chlorin fumes 729 

168. Virginia creeper, strawberry and rose leaves injured by tar fumes 733 

169. 170, 171. Apples injured by spraying with Bordeaux mixture 763, 764 

172. Apple leaf with dead spots and holes after spraying with Bordeaux mixture.. 765 

173, 174, 175. Scarification wounds 777, 778 

176. Hollow pine trunk 779 

177. Section of trunk of Picea vulgaris with overgrowth of the resin channels. .. .780 

178. Overgrowth of the cut surface of a branch 783 

179. t8o, 181. Cross-section of a year-old cherry branch 786 

182, 183, 184, 185. Ringing wound on a grapevine 789-795 

186. Callus formation from young bark cells in a barked trunk 802 

187, 188, 189. New tissue formation on a barked cherry trunk 805-808 

190, 191, 192, 193, 194. New tissue formation at bend in an apple twig 811-813 

195. Injury to a branch due to twisting 815 

196. Constriction in branch due to a wire ring 819 

197. Fuchsia cutting 822 

198. Rose cutting 823 

199. Budded rose 832 

200. Bark graft of Aesculus, with adventitious buds 837 

201. Pine with natural in-arching of a second trunk 848 

202. Stoppage of ducts in a grapevine, due to wound decay 853 

203. Alder root, barked by the tread of feet 856 

204. Gnarlly overgrowth cap of the stump of an oak branch 860 

205. Bark tubers from an apple trunk 866 

206. Isolated wood centers in the bark of a year-old pear branch 869 

207. Callus formation in a leaf of Leucojnm vernum 872 

208. Leaf cutting of a begonia 875 



MANUAL -f^„ 



OF 



Plant Diseases 



BY 



PROF. DR. PAUL SORAUER 

II 



Third Edition—Prof. Dr. Sorauer 

In Collaboration with 

Prof. Dr. G. Lindau And Dr. L. Reh 

Private Docent at the University Assistant in the Museum of Natural History 

of Berlin in Hamburg 



TRANSLATED BY FRANCES DORRANGE 



Volume I 
NON-PARASITIC DISEASES 

BY 

PROF. DR. PAUL SORAUER 

BERLIN 



WITH 208 ILLUSTRATIONS IN THE TEXT 



SIS 7-3 






Copyrighted, 1914 

By 

FRANCES DORRANCE 



GEP 29 1914 

©CI.A380596 

THE RECORD PRESS 
Wilkes-Barre, Pa. 



PREFACE TO THE GERMAN EDITION. 



For the third edition of my manual I have requested the assistance of 
Professor Dr. Lindau and Dr. Reh. In the second volume of the work, the 
former has treated of vegetable parasites and in the third volume the latter, 
the animal enemies of plants. 

Such help seemed necessary because, since the appearance of the second 
edition, the published results of investigations have been so numerous that 
too long a time would have been required for mastering the material. Other- 
wise when the last sheets appeared the first would have become obsolete. 
Even with this division of the work, this unfortunate condition has not been 
entirely overcome and an attempt has been made to obviate the difficulty by 
listing some of the more important recent material in a supplementary biblio- 
graphy. If the absence of some works, especially of the earlier literature, is 
noted the explanation lies in the fact that we have emphasized especially 
those studies necessary for the support of our presentation of the subject. 
A more detailed bibliography would be possible only if the individual diseases 
were treated in monographs. 

I kept for my own work the revision of the first volume, comprising the 
non-parasitic diseases. The fact that this volume is the most extensive is ex- 
plained by my standpoint, already sufficiently characterized in the preface to 
the second edition, — because I lay the chief weight on a knowledge of the 
diseases produced by atmospheric, soil and cultural conditions. The distur- 
bances caused by these factors are not only the most abundant and perma- 
nent but also often form the starting point for parasitic diseases. 

On this account, supported by my own studies and the observations of 
other investigators, I was especially anxious to show how the same plant 
species could be changed structurally and in habits of groAvth according to 
position and the constitution of the soil. Individuals are sometimes more 
disposed to a definite form of disease or are more resistant to it, according 
to the difiference in their constitutions. 

This holds good also for their behavior towards parasitic organisms. It 
is thus evident that not only must the latter be combatted by directly destruc- 
tive methods but also the chief emphasis should be laid on the possible con- 
stitutional change of the host plant. Therefore, we will find the most essen- 
tial task to be the breeding of resistant varieties. At the time the first 
edition of this work was published, the undersigned stood alone as represen- 
tative of this theory of predisposition to parasitic attack, but now many of 
the most prominent investigators are counted among its supporters. 

And thus I hope that the idea for which I have fought since the be- 
ginning of my scientific activity, that is, the formation of a rational plant 



hygiene, will finally come to full recognition. Primarily, we must learn to 
protect the organism from disease, and then, through force of necessity, may 
take steps to heal an organism which is already diseased. 

In the first volume, the first section of the introduction treats of the na- 
ture of disease, while the second takes up the history of its investigation. It 
should be understood by the term "historical" that I did not wish to write a 
history of phytopathology, which would have taken much more thorough pre- 
liminary study, but did consider it desirable to attempt to sketch the process 
of the development of this branch of knowledge, in order to show how the 
present point of view had developed in the course of time. 

In looking through the specialized part, the reader may also find that 
even in the present edition conclusions once based on a considerable number 
of my own investigations have been abandoned. The aid of illustrations, so 
absolutely necessary in phytopathology, has been made use of to an appreci- 
ably larger extent in describing diseases. In accordance with the character of 
the book, new anatomical drawings especially have been added. In the vol- 
ume on parasitic diseases many tables have been gathered together for the 
sake of comparison, in order to make clear to the reader the different genera 
of one family in their distinctive characteristics. 

The new drawings were made by Fraulein H. Detmann and Fraulein E. 
Liitke, whom I thank very much for their work. 

Most of all, however, I wish to thank my collaborators. With me, they 
had to solve the difficult problem of presenting the material in a space deter- 
mined by contract before the revision. During the revision, we found our- 
selves confronted by the cjuestion either of giving to the whole subject a 
briefer form than was originally intended, or of working up some chapters 
in detail while summarizing others. We chose the latter course and treated 
the seemingly most important sections thoroughly and the groups, which had 
been sufficiently worked over in other books, in a correspondingly limited 
way. 

Schoneberg, October, 1908. 

PAUL SORAUER. 



INTRODUCTION. 



Section I. 
THE NATURE OF DISEASE. 



I. Limitation of the Conception of Disease. 

Our first task is evidently the necessity for defining the province of 
which we will treat and for expounding what we understand by the term 
"Disease." 

If we call "sick" only those cases in which the organism undergoes such 
a disturbance in its functions that its existence seems threatened, we will be 
in a dilemma when we consider the changing developmental forms of our 
cultivated plants, for we will then discover that the above explanation is in- 
sufficient. We know, for example, that our species of cabbage, kohlrabi and 
cauliflower are descended from a plant similar to bank-cress which, in its 
natural development as a wild plant, shows no tendency toward the forma- 
tion of large leaf -buds such as cabbage heads, nor of root-like sw^ellings of 
the stem, as kohlrabi. These vegetables have been produced by selection and 
cultivation and are characterized by a condition which we term parenchy- 
matosis, because the woody elements have been replaced by a tender 
parenchyma, due to the high degree of nitrogen continuously supplied from 
generation to generation. In dry, hot summers young plants grown on soils 
poor in food materials begin to show a marked ripening and, in connection 
with this, a reddish blue tone in their leaves. In case kohlrabi, under such con- 
ditions, makes any development worth mentioning, it becomes "stringy," 
that is, its flesh is traversed by tough, hard fibres, making it "woody." Investi- 
gation shows that the kohlrabi plant by the curtailment of the supply of water 
and food materials is well on the way toward again developing a wood-ring 
with prosenchymatic elements, as found constantly in the wild plant. Very 
similar conditions are found in carrots in which our normal uncultivated 
plant possesses a solid woody root, rich in starch. Our cultivated varieties, 
on the contrary, have become thick, fleshy structures ; the best containing no 
starch at all but the greatest possible amount of sugar. Only in the so-called 
fodder varieties, as, for example, the white giant carrot, is still shown an 
abundance of starch. Hofi'mann-Giessen has experimentally developed our 
cultivated carrot back to the wild form. 

Now, is the cultivated form a diseased condition since it actually suc- 
cumbs more easily to certain disturbing influences, or is the reversion of the 



cultivated plant to the normal wild one to be considered a disease ? In any 
case this reversion is a condition which must be combatted as it is evidently 
unfitted for our cultural efforts. 

In considering such examples we see that, in treating questions of dis- 
ease, we shall have to follow two lines of work. We must naturally first 
keep the organism's aim in sight. And this aim, which the organism derives 
from its very origin, is to live, and in fact to live as long as possible. Every- 
thing which has once been originated ])ersists as the effect of the causes 
leading to its production, until a stronger factor arises which disturbs the 
fixed order and brings about other groupings of material, form and function 
(an inseparable trinity). But, up to the time of interference of such a factor, 
the developed individual, with the sum total of the forces inherent in its 
substance, maintains its then existing order, that is, its individuality, to which 
a generally definable age limit is set. This necessary mechanical defense of 
its individuality against the constant attacks of exiernal factors may be 
termed the "force of self-preservation." In following the second line, the 
aim of cultivation, developed from the relation of the plants to human needs, 
is an added important factor. These conditions of the vegetable organism 
opposing our cultural endeavors will be combatted as inexpedient. But such 
conditions need in no way threaten the existence of the individual and there- 
fore, according to the above explanation, are not diseases. Yet they belong to 
the province of the pathologist as disturbances which must be considered 
and overcome. 

In limiting the conception of disease, we meet with similar difficulties in 
double blossoms, in as much as this doubleness is due to the fact that the 
stamens have been changed into petals and in doing this have deformed the 
pistil. This leads to sterility. The length of life of the individual plant is not 
injured in any way by this sterility, but, on the contrary, is actually length- 
ened as, for example, in double petunias. But the aim of the species is 
affected since such double blossoms are no longer able lo^ produce seeds. If 
this kind of doubling becomes general, such species unist die out in case all 
vegetative reproductive organs are missing. This variation in structural 
development, threatening the existence of the species, however, is 
directly sought for in cultivation and any reversion to the normal, seedbear- 
ing form is selected out. Here indeed the aim of cultivation contradicts the 
natural aim and pathology tries hard to overcome the natural trend opposed 
to the momentary direction of the cultivation, although in doing this, it di- 
rectly threatens the existence of the species. 

Such antagonisms are very numerous. In the list of cases in which 
only individual organs become diseased, one such local disturbance can in- 
fluence injuriously the organism as a whole, but can yet be useful to the 
mdividual. We would call attention here to the dropping of young fruit due to 
drought. The cultural aim is naturally interfered with but the economy 
of the tree reaps the benefit in as much as it saves the reserve materials, 
which would have been used in maturing the fruit. As a result of this, the 



tree is not only in a position to develop the next set of leaves, but also to set 
numerous fruit buds, which would have remained suppressed had a full crop 
exhausted the store. When late frosts injure the blossoms and young fruit, 
the individual organs are certainly severely sickened and fall off later ; but 
the tree itself has the advantage of saving a quantity of food material. As 
often happens, the cultural purpose can also profit in this case, because the 
blossoms developing after the action of the frost yield more perfect fruit 
and thus an increased revenue. 

This defines clearly the difference between pure and applied science. 
Pure science studies the process of disease in itself and can be only cellular 
pathology, while applied science takes into consideration the effect on the 
diseased individual and its agricultural significance. We must unite both 
forms of science since we take the purely scientific studies as the basis of 
our consideration and explanation of the economic effects of the attack of 
sickness. 

The consideration of the cultural needs forces us to the following 
division of our subject; first of all, we will have to consider all cases which 
threaten the individual aim of the organism, i. e. its longest possible life;— 
these are absolute diseases. Then we must discuss the disturbances which 
the momentary cultural aim experiences and which we term relative diseases. 
I'hese relative diseases may vary since what cultivation considers worth striv- 
ing for to-day may be neglected to-morrow. For example, with savoy, every 
reversion of the plant to Brussels sprouts is a disturbance of the cultural 
aim to be avoided by changing the seed. If we intend growing Brussels 
sprouts, however, each variation of these plants toward the savoy form is a 
deterioration, undesirable in cultivation. Finally, malformations are usually 
unimportant agriculturally but must be considered. Such malformations 
may be a maturing of organs in a manner differing from the usual process 
of development. These natural occurrences, which, we believe, may often 
be traced back to changes in pressure conditions and other mechanical in- 
fluences due to the formation of the organs, constitute a special branch of 
knowledge, — Teratology. This is, however, to be considered as one branch 
of pathology and we will have to draw into our discussion these phenomena 
so far as their causes are known or may be surmised with some certainty. 

The method of treating the material which falls under the province of 
the study of plant diseases or Phytopathology, will have to be according to 
the following scheme : — ■ 

I. Paihography or symptomatics, i. e., the description of the 
disease according to its individual signs or symptoms. 

II. Pathogeny or etiology, namely, investigation as to the cause 
of the disease. Only after the causes are known is it possible to 
bring into use 

III. Therapy or the study of healing methods and to draw 
into the discussion 

IV. Prophyla.vis or some method of prevortion. 



2. The Production of the Disease. 

If we have said that we must begin with the individual cells when judg- 
ing a disease, we must know first of all how complicated an organism the cell 
is and how its structure and function depend on the constitution, position 
and action of the micellae composing it. 

Let us, for example, examine some efifects of "swelling." The cell wall 
at a given time is saturated to a definite degree with water of imbibition, that 
is, the cellulose micellae held together by cohesion are provided with a water 
sheath with a certain amount of distention. The micellae will be separated 
further from one another or will approach one another more closely as the 
water supply varies; that is, the walls will sometimes become more dense, 
sometimes more flaccid. Such fluctuations are brought about in the protoplasm 
of the cell by the action of substances which withdraw water osmotically. 
Similar processes are observed in chloroplastids, for example, in grain leaves 
if acted upon by weak chlorin fumes or by sulfuretted hydrogen. The chlo- 
roplasts are seen to shrivel with the use of chlorine while the chlorophyll 
grains become pale green, doughy, almost gelatinous bodies with sulfuretted 
hydrogen. 

In the cell wall, marked phenomena of flaccidity may often be restricted 
to single spots. The so-called "bead-cells" in winter grain may be taken as 
examples of this. Individual cell groups near the larger vascular bundles 
show bead-like convex centres of flaccidity on the inner side of their walls, 
which later lose their cellulose character. If young, vigorously growing 
potato stems are exposed to frost, different groups of leaf parenchyma cells 
will be found later whose walls seem swollen in lines to four times their 
normal thickness. In this may be observed the browning and decay of the 
more dense wall lamellae into stripes which lie imbedded in a homogeneous, 
lighter parenchyma. 

In the case of very flaccid membranes, however, molecules will be able 
to penetrate the greatly enlarged micellar interstices, v/hich cannot force an 
entrance through the smaller ones, because of their size. If changes in the 
constitution of the protoplasm have been caused by frost, we find substances 
passing in and out which could not have been transferred before by the 
plasma body. The red coloring matter and the sugar in frosted red sugar 
beets (Beta) pass easily from the parenchyma of the beet into the surround- 
ing water. This would be impossible in the cut beet, if it had not been 
frosted previously. The loosening of the structure of the organic substance 
is a very normal process the intensity of which depends on the action of ex- 
ternal factors, such as water supply, light, warmth, etc. If these normal 
processes exceed a certain limit, they lead to disturbances which so alter the 
structure and function of the cells that they become unable to maintain life. 
Every other process of cell life may be similarly afi^ected. Under the influ- 
ence of different factors of growth, the process may be hastened or retarded. 
We know that each fife function oscillates between wide limits, according to 



the action of each individual vegetative factor. We call these limits the 
minimum and maximum and the degree of functioning at which a life pro- 
cess most favors the development of the organism the optimum. 

The field of oscillation of the functions about the optimum, ivithin the 
limits promoting development may be called the "latitude of health." This 
should not be confused with "tlie latitude of life," for the organism can still 
live outside the latitude of health, but its functions are so weakened that its 
development undergoes arrest or retrogression and this condition is disease. 
If this cessation of the function is temporary, the condition falls under the 
conception of "check" and we speak of check from cold or from darkness, 
etc. But we must guard against the belief that the appearance of sickness 
or a condition of check or of death in any species is connected with any pre- 
cise numerical values for the separate factors of growth. If, for example, 
we take two cuttings from the same plant and cultivate them for some time in 
sand sterilized by heat with the same quantity of food materials but keep one 
cutting in a hot house and the other out of doors, in the end the tv/o will 
show a very different susceptibility to frost and other atmospheric factors. 
The specimen grown in the hot house freezes more easily ; that is, its mini- 
mum for the maintaining of life is raised. Temperatures, at which the speci- 
men grown in the open air remains within the latitude of health, arrest the 
life processes of the hot house specimen. Experiments to determine the 
maximum and minimum of other factors of growth show .very similar 
variations so that we may arrive at the conclusion that for each habitat each 
plant has its own scale of needs, its oiun optimum, maximum and minimum 
and therefore possesses its ozvn specific latitude of health. 

Further, the circumstance that the dift"erent functions are lost at differ- 
ent times should be considered. If, for example, potato tubers are left for 
some time at a temperature of about — i°C., it will be found that respiration 
ceases sooner than the conversion of starch into sugar. This results in an 
accumulation of sugar in the tuber which is called "turning sweet of the 
potato." If the temperature is raised more slowly to possibly -\-io°C. the 
stored sugar disappears through the increased activity of Ihe protoplasm and 
respiration. If cucumbers, tobacco and other heat loving plants have to 
withstand a temperature of +5° to 8°C. for some time, they show a yellow- 
leaf condition, which disappears with continued increase of heat. The 
plants do not die, but assimilation and growth are so suppressed that proces- 
ses, such as the formation of gums, may be introduced, leading to the prema- 
ture death of the individual. As in the preceding case of deficient heat, 
deficiency in food materials or light, — in short, every decrease of any vege- 
tative function, — so retards the normal direction of the functions that the in- 
teraction of these for the purpose of a beneficial metabolism is misdirected. 
Other combinations and functional directions (for. example, fermentations) 
are now produced, which initiate the ending of life prematurely. The same 
effect will necessarily appear every time the maximum of any vegetative 
factor is exceeded, or even approximated. 



lO 

In very many cases a sickness which has already set in is indicated by 
chlorosis, beginning inconspicuously and progressing slowly. Even if it is 
possible to observe the very beginning of chlorosis, the beginnirig of the sick- 
ness itself has in no way been discovered since the first molecular changes, 
which have led to the yellowing of the chloroplast, still remain unknown to 
us. The boundary line where any single factor of growth ceases to be bene- 
ficial and becomes a retarding factor may indeed be determined experiment- 
ally but in this we see only the final result and not the course of development ; 
i. e., the processes initiating this final result. vSo far as our powers of obser- 
vation are able to discover, hcalih and disease represent conditions icliich 
imperceptibly pass over into one another. 

3. The Relation of the Plant to its Environment. 

In the attempt, undertaken in the previous section, to demonstrate how 
health and disease present interdependent conditions like the links of a chain, 
we kept in view first of all the so-called constitutional diseases. By this are 
understood the disturbances in nutrition which influence the whole organism 
sympathetically and are the results of deficiency or excess of one of the 
necessary vegetative factors. Local diseases due to accidental interference 
must be opposed to these general diseases. In them the organism as a whole 
in its full reactionary capacity is exposed primarily to a disturbance affect- 
ing only one individual organ. While the action of the necessary inorganic 
factors of growth come under consideration in constitutional diseases, in 
local diseases the important influences are those mutually exerted on one 
another by the organisms. 

There are insects which seek out the plants in order to satisfy their 
needs for nutrition or for habitation, or the plants themselves mutually in- 
fluence one another. We find as the most pertinent example the influence of 
street trees on the plants growing on the other side of the hedge row. We 
notice especially in times of drought that the grain and potato plants found 
within reach of the tree's shadow are not only weaker in development but 
wilt sooner and to a greater degree than the other plants in the same field. 
This disadvantage is due chiefly to the tree which keeps off the rain and its 
roots which withdraw the soil water. In the field itself we frequently find 
different places in which the seed has grown very poorly because the wind 
grass has choked the grain. The seed was not sown too thin but the germi- 
nation and first development were choked by cold and deficiency in oxygen 
because of impervious spots in the field. In spring the soil does not dry so 
quickly in these places and the moisture is retained longer; the soil conse- 
quently warms up less easily and suffers for need of oxygen. The wind 
grass (Apera spica venti) which occurs everywhere in grain fields is less 
sensitive and under such conditions develops more quickly than grain. 
Because of its greater size, it chokes out the seedling grain. Similar con- 
ditions arise in connection with other weeds, which, developing more rapidly, 
not only take food materials out of the soil and away from the cultivated 



II 

plants, but also injure them b}^ shading. Actually, howcA'cr, this struggle for 
room is the factor first manifested in each plant community and makes itself 
felt in all field and forest plantations. In the grain field and in every forest 
tract, the individual first grooving most strongly chokes out its weaker neigh- 
bors. It is the universal question of the strong driving back the weak which 
must find expression in all community life. 

The kind of community life just described in its relation to spacial sep- 
aration can be termed neighborhood in distinction from the mutual influenc- 
ing of organisms when united in space. A relationship of this latter kind 
(symbiosis) must be the more intimate since one organism lives with the 
other. De Bary (1866) distinguished a miitualisiic symbiosis from an 
antagonistic, according to whether the influence is mutually beneficial or 
detrimental. The terms chosen by A^uillemin (1889) for this relationship 
"symbiosis" and "antibiosis' seem less fortunate to us. We find examples 
of a mutualistic community also termed commensalism by van Beneden in 
1878, as companionship at table, in the little bunches of roots of the sago 
palm (Cycadeae) which occur on the surface of the soil, rigidly branching 
like witches' broom^s and which harbor numerous chains of Nostoc in the 
large holes in their bark. The genus Gunnera shows similar conditions. 
Further, the case is often mentioned in literature, in which a water plant, 
Azolla caroliniana, resembling our Salvinia nutans, in the axillary hollows of 
the leaves, gives shelter to another Nostoc with longish members (Ana- 
baena). The most accessible example of mutualism is offered by the struc- 
ture of the lichen body, in which fungus and alga remain connected per- 
manently, to their mutual benefit, — Lichenism. 

In the same way may be explained the s}mbiosis of certain mycelia and 
the roots of Fagus, Corylus, Castanea and some conifers, the so-called root 
fungus or mycorrhiza which is usually considered a necessary and universal 
arrangement. In connection with the mycorrhiza should be mentioned the 
protective device called Bacteriorhiza by Hiltner^ and Stormer (in 
Beta and Pisum). Bacteria penetrate from the soil into the outer cell layers 
of the roots, actually causing a browning of these layers, but otherwise not 
especially disturbing the health of the plant. According to Hiltner, however, 
these bacteria prevent the penetration of other injurious organisms (Phoma, 
etc.). 

Finally we will consider the arrangement of root tubercles, which may 
be found in different forms and grouping on the roots of the Lcguminoseae 
and form those well-known grape-like bodies in alders, which not infre- 
quently may be observed as spherical nests of short branched roots as large 
as one's fist. The organisms in the tubercles making the nitrogen of the air 
available for the plant and described by the students of legumes as Rliiz- 
obium Lcguminosarum Frank, or Bacillus radicicola Beijerinck, are bacteria 



1 Hiltner and Peters, Untersuchungen iiber die Keimling-skrankheiten der 
Zucker- und Runkelriiben. Arbeiten d. Biolog-. Abt. am Kais. Gesundheitsamte. 
Vol. IV. Part 3. 1904. 



12 



just as the producers of the silver white tubercles in Isopyruin hitcrnatum 
which, according to MacDougal^ develop extensively in soils free 
from nitrates. On the other hand, the recent investigations of Bjorkenheim- 
seem to prove that a fungus is concerned in alders. 

In antagonistic symbiosis, de Bary has used the expression saprophytism 
and Johow in 1889 defined the idea more closely by distinguishing holo- 
saprophytes (those lacking chlorophyll) from Iicniisaprophytes (those con- 
taining chlorophyll). 

Bischoff has contrasted with this the conception of parasitism. Ac- 
cording to Sarauw^ the expression "parasite" was brought into use in 1729 
by Micheli f6r the Balanophoreae*. In agreement with the classification of 
the saprophytes, Sarauw has distinguished holo parasites (those without 
chlorophyll) from hemiparasifes (those provided with chlorophyll). 

Saprophytism is the ability of an organism to take its nourishment from 
decomposing organic substances, while the parasite drav/s nourishment from 
the living organism. If we test this classification, based on the forms of 
nutrition, we find that here, as in all branches of science, a sharp systematic 
subdivision is assumed only by representatives of a young school, while those 
of the older and more experienced school are convinced that transition forms 
exist between the dift'erent groups. 

If relative adjacency be compared with nutrient association (symbiosis) 
each forest and each grain field shows how constantly one organism influences 
the other, according to whether the one leaves any food materials, water and 
light, for the other. Just as spacial separation sets no fixed limitation to the 
form of nutrition, the sub-division of the organisms into those with purely 
mineral nutrition and those dependent on organic substances should be 
abolished. 

Although plants suited for independent self -nourishment can draw their 
nutrient material from purely mineral substrata, yet the process actually 
present consists in their taking humus substances which furnish the food 
materials in an easily absorbable form because of the activity of a rich bac- 
terial flora in the soil. The advantages of supplying our fields with animal 
manures should be thought of in this connection. 

Modern views have strongly modified this distinction between sapro- 
phytism and parasitism, since they have brought forward numerous exam- 
ples showing that the organisms called obligate parasites may become de- 
pendent on saprophytic nutrition in definite developmental phases and con- 
versely that saprophytes in many instances can assume the parasitic mode of 
feeding. Miyoshi's^ investigations give us a clear insight into the way 



1 Minnesota Botanical Studies 1894. * 

2 Bjorkenheim, Beltrage zur Kenntnis des Pilzes in den Wurzelanschwellungen 
von AInus incana. Zeitschr. f. Pflkr. 1904. p. 129. 

■'• Sarauw, G. F. L., Rodsymbiose og Mykorrlizer saerlig hos Skovtraerne. Botan- 
isk Tidsskrift 1893. Parts 3 and 4. 

■i But Tournefort in Mem. Ac. Paris 1705, p. 332, speaks of plants which grow on 
other plants. 

5 Miyoshi, Manaba, Ueber Chemotropismus der Pilze. Bot. Zeit. LII, 1894, pp. 
1-27. 



13 

m which such a change takes place in nutrition. The experiments under- 
taken at Pfeffer's Institute in Leipsic show that fungus hyphae are irritable 
chemically and that the direction of their growth may be influenced either 
towards the stimulating substance, (positive chemotropism) or away from 
it (negative chemotropism). Indeed their mode of growth also can be 
changed since, for example, a tendency towards sprout formation sets in with 
a higher concentration of the solution. The commonest mold species, which 
occasionally become parasitic (Mucor, Penicillium, Aspergillus) show an irri- 
tability with substances which almost always can be presupposed to be char- 
acteristic of phanerogamic plants. Besides dextrin and the neutral phosphoric 
acid salts, sugar especially attracts fungi, in case the concentration is not 
too high. Thus, for example, grape sugar in a 50 per cent, solution acts repel- 
Icntly for Mucor stolonifer, the active agent of decay of fruits. A.cids, on the 
contrary, and alkalis from the beginning act repellingly. The germination 
tubes of the summer spores of Urcdo linearis, a grain rust, are attracted by a 
decoction of plum and wheat leaves. Especially interesting are the cultural 
results with Penicillium glaucum, whose hyphae bore through the cell walls 
of a leaf impregnated witJi a 2 per cent, cane sugar solution. In the same way 
they penetrated artificial cellulose membranes and the epidermis of bulb scales 
which lay on a nutrient gelatine. 

These are especially important clues capable of explaining the numerous 
case of sickness from Penicillium. It is well known that this mold, the 
most abundant agent of decay in stone fruits, first begins to spread when the 
ripening process has converted the starch into sugar. 

In connection with the penetration of Penicillium into the scales of 
bulbs, we find abundant examples in the cases of decay in the tulip, hyacinth 
and lily bulbs which occasionally lead to lawsuits. This decay occurs especially 
extensively when wet years prevent the maturing of the bulbs or if the bulbs 
are stored when containing an unusual amount of sugar and then used pre- 
maturely for forcing. 

Thus we see hozv the cell contents and the cell ziolls of the host plant 
can determine the penetration of hyphae and the transition of the saprophyte 
into a parasite. 

4. Parasitic Diseases. 

Supported by various carefully studied cases of parasitism, many ob- 
servers so generalized the conception of parasitic diseases that they assumed 
them to be present wherever organisms are found gathered together. In 
many cases this is supported by experiijients in which the parasitically living 
organisms were injected into the host and were able to produce a local dis- 
ease in the tissue. 

With this method the apparent proofs of parasitic disease were accumu- 
lated in such a way that one was forced to the assumption that there could 
be scarcely any disease which was not caused parasitically. Infection ex- 



14 

periments in the laboratory led gradually to the knowledge that in many 
cases of 'disease no specific parasites were present but universally distributed 
fungous and bacterial forms. The further the studies advanced, the more 
cases were listed in which inoculation with spores of the most common 
molds, as Botrytis, Penicillium, Cladosporium etc., also the most widely dis- 
tributed soil bacteria. Bacillus subtilis and B. vidgatus, develop disease in 
healthy tissue. And finally was recognized the importance of the question 
how organisms universally present could at times be parasitic in their mode 
of life and, at other times, saprophytic. Corollary to this question is one 
which was deduced from rapidly increasing discoveries in many experiments 
with the same methods of infection; certain varieties or even individuals 
were resistant while others succumbed easily to the parasitic attack. What 
is the cause of such dififerences? 

Some of the investigators brought forward the theory of virulence as 
an explanation of such cases. It was emphasized that in each separate case 
parasitism as a struggle between two organisms had depended necessarily 
upon which was the stronger. If the weapon of attack of tjie parasite, for 
instance, be an enzyme, able to dissolve the cell walls of the host, then it 
would be explicable that this process would take place more quickly in pro- 
portion to the increase of solver.t ferment formed in any given unit of time. 
Since it was now possible to prove experimentally that the strength of the 
attack varied in cultures of different nutritive substances, it could be said 
that, where it became the active agent of disease and its production of enzy- 
mes especially abundant, it must have been especially virulent. Bacterial 
cultures furnished the greatest number of examples of change in virulence. 
Yet such cases were also determined with fungi. De Bary's statement con- 
cerning the frequently encountered mold, Balryiis cinerca, is well-known. 
He states that the mycelium must develop by the customary saprophytic 
form of nutrition up to a certain strength before it becomes parasitic and 
successfully attacks the living parts of the plants. I succeeded in getting 
like results with the conidia of this fungus. Masses of spores were strewn 
on delicate Begonia leaves and kept very damp. After several days it was 
possible to observe that, where these spores had lain in thick masses, the leaf 
had become diseased, showing a browning of the tissue. Where the spores 
had lain isolated, however, no attack could be discerned. The action of the 
quantity of ferment excreted by the individual spores therefore proved in- 
sufficient, while the excretion from a mass of spores brought about infection. 
It can thus easily be understood that parasites, like every other organism, de- 
velop most strongly when the nutritive conditions are most favorable and 
that the stronger and the more abundant the formation of their vegetative 
organs, the greater the excretion of the enzyme and accordingly the increase 
in strength of their attack. Therefore their virulence is raised. 

But these processes are not sufficient to explain the fact that in one field 
when a number of varieties are grown in a single plantation, certa'n ones 
may be completely destroyed while others standing next are but little injured. 



15 

or perhaps absolutely iinattacked. Since in such cases the parasite is quickly 
and extensively distributed on one variety and not on the other, although the 
atmospheric conditions and other factors of vegetation are equally favorable, 
the specific constitution of the host plant in these two cases must have deter- 
mined whether it would become diseased. Thus vve arrive at the conclusion 
that for the production of a parasitic disease the presence of the parasite 
alone is not determinative but the constitution of the host organism is also 
a determining factor. 

The many infection experiments have led to a classification of the living 
creatures infesting other organisms and capable of attacking the tissue, in 
which one group is described as obligate parasites when able tc attack the 
host plant in all stages of its normal development. Of this group there have 
been separated as zvound parasites all such organisms as cannot attack the 
organism possessing normal protective devices but need the changes in tissue 
offered by the surface of a wound. In a great many in?tances, however, we 
have recognized the fact that the parasite only finds the environment re- 
quired for its development when the host has been affected and its functions 
weakened. Such conditions will appear here as were also decisive in the 
experiments carried on by Miyo.shi (see preceding section). This group 
bears the name "parasites of weakness." 

To this last group especially belong the numerous species which during 
many generations live on dead organic substances. They therefore must be 
spoken of as saprophytes which occasionally become parasitic, — facultative 
parasites. Therefore the boundary between parasitism and saprophytism is 
lost here and even in those species which are always parasites (obligates), 
such as the varieties of smut, we find developmental phases with a sapro- 
phytic mode of nutrition. 

If we now, however, study more closely the families of our closest para- 
sites among the fungi, namely, the smuts and rusts, we will find one fact 
brought into prominence by the most recent investigations and repeatedly 
substantiated; namely, that the energy of grozvth of the parasite depends on 
the host plant. We have examples proving that the same fungus occurs in 
different species of the same host genus in the same habitat, sometimes grow- 
ing luxuriantly in many large centres, sometimes sparsely in small forms, 
according to whether the one species has fleshy leaves and the other thin 
ones. Indeed, the rusts are so dependent upon their host plants that biologic 
races are formed which, agreeing formally, nevertheless show differences in 
adjusting themselves to definite host plants and either cannot develop at all, 
even when carefully injected upon a related host plant, or develop only 
slightly. Thus we have a special form of the common black rust of grains 
on rye, another on wheat, another on oats etc. Mycologists cherish the con- 
viction that this development into individual races through the accommoda- 
tion to a special host plant is a widespread phenomenon constantly increas- 
ing. What else can such a race formation indicate than that parasites in 
their demands have been and still will be most closely connected with the 



i6 

constitution of their suhstraiiimf If, however, as previously shown, the 
closest parasite is thus very dependent upon its host plant, it only goes to 
show how completely it agrees with non-parasitic plants in its demands for 
very definite nutritive conditions, and that with a change in these the para- 
site changes its character and either adjusts itself or disappears. Stahl's 
observations^ on myxom.ycete plasmodia show that we must take 
these phenomena of adjustment into consideration. If the water in the cul- 
ture glass was replaced by a ^2 per cent, grape sugar solution, the plasmodia 
either died from this sudden change or shunned the sugar solution. Grad- 
ually, however, they accepted it, having accustomed themselves to a more 
concentrated solution (perhaps by a certain loss in v/ater) and indeed in 
such a way, that, replaced in pure water, they showed considerable injury. 

In regard to the formation of races, Pfeffer- expresses himself 
thus ; "Present discoveries . . . make it clear that the tropistic reaction 
of the same species of bacteria, flagellates etc. gradually changes in accord 
with the existing cultural conditions. Thus it should be understood that in 
the same species in nature and in artificial cultures there is found at times 
a very appreciable ability to respond to reactions and changes, varying to a 
disappearing point, according to a definite stimulus. Indeed after wide ex- 
perience it seems possible to breed races in which a definite reaction to 
tropism has been partially or entirely lost." 

Parasitism is nothing extraordinary. Possibly it is not a factor which 
has newly appeared since plant cultivation was begun. It should be con- 
sidered as a nutritive form which arose gradually with the developrhent of 
organic life and a necessary one, to be looked upon as the last link in the 
chain formed by the mutual interaction of organisms. This last link begins 
with those organisms which have the ability of forming organic substances 
from inorganic material through the action of light. Joined to these are the 
plants with the lesser need of light, such as are found among the bacteria 
living in humus where an addition of quickly decomposible organic sub- 
stances presents essential aid to the nutritive process. As the struggle for 
light gains in importance with an increasing number of organisms, the more 
pertinent becomes the development of groups of organisms requiring but 
little light and an ever greater need of a method of nutrition by which the 
raw material is offered in the form of organic, easily re-worked substances. 
Such conditions are found at present in saprophytism. 

With the struggle for light in the case of a constantly increasing num- 
ber of individuals comes also the struggle for space. In the course of time 
the lack of space will lead finally to those forms of adjustment in the plant 
world which require soil for their habitat only in the beginning, if at all, and 
have chosen some other organism as a centre of colonization. The mutual 
interrelations forming under such conditions are partly friendly, partly hos- 
tile, just as they occur in mutualistic and in antagonistic symbiosis. 



1 Stahl in Bot. Z. 1884, pp. 163-66. 

2 Pfeffer, Pflanzenphysiologie, 2 Edition. Vol. II, p. 763. Leipzig 1904. 



17 

Among the species of plants using some other organism as a habitat, we 
find the formation of very different devices for the means of nutrition. Be- 
ginning with lichens, the assistance given by thalH acquires greater and 
greater significance, up to the formation of a myceHum. The myceHum is 
satisfied with dead bark, or rather that attacked when dying, or with the 
leaf substance of its host, or it can only eke out its existence when, with the 
help of the enzyme which it excretes, it attacks the living organic substance 
and then calls parasitism into existence. 

But in all these relations the one fundamental law becomes evident that 
each organism is associated with the definite constitution of its substratum. 
This substratum must have the exact requirements for satisfying all the de- 
mands of the organism, otherwise it cannot thrive. Therefore all the organ- 
isms which we call parasites make very definite demands on some host. How 
narrowly limited these demands may often be is shown di recti}' by the bac- 
teria, for which at times slight fluctuations in the amount of heat, the acidity 
of the nutritive mixture etc., lead to the replacing of certain species by others 
better adjusted. 

In order to cite only a few new examples we will mention the investiga- 
tions of Thomas Milburn^ who cultivated fungi as well as bacteria. 
Of the former he found in the case of Hypocrca rnfa that an increase of 
osmotic pressure first suppresses the formation of pigment in the conidia 
and finally inhibits the formation of conidia. In this fungus the color of the 
conidia changes with the reaction of the medium. If the reaction is acid, 
green spores are formed; if alkaline, yellow spores. A well nourished 
mycelium forms no fruit in the dark but does develop conidia when poorly 
nourished. The yellow color of the mycelium of Aspergillus niger is very 
sensitive to light and when exposed to it turns black within a few hours. The 
Bacillus ruber balticus found on potatoes, the so-called "Kieler bacillus"^ 
which, according to Laurent, forms acids on certain nutritive soils and al- 
kalis on others, is so influenced in its production of coloring matter by the 
nutritive substratum that it develops a violet color on an acid substratum and 
orange red on an alkaline substratum. 

Lepeschkin'* observed that the strictly aerobic bacteria from the 
sputum in pneumonia. Bacillus Berestnewi, can develop a branching growth 
on strongly alkaline and on strongly acid substrata, but gradually acidifies 
the alkaline substratum. In the presence of sugar (dextrose) a pinkish color 
appears together with the disintegration of the little rods into oidia. In 
the presence of larger amounts of nitrogen compounds (aspargin, lecithin, 
peptone) the whole mass of bacteria turns yellow. The optimum for growth 
bes probably at 25°C. Even at 35°C. the bacterium grows very slowly and 
at 38°C. is no longer able to grow. It is killed at 55°C. 



1 Thomas Milburn, Ueber Aenderungen der Farben bei Pilzen und Bakterien. 
Centralbl. f .Bakteriologie usw. II. Division 1904. Vol. XIII. Nos. 9-11. 

2 See Breunig, Unter.suchungen des Trinkwassers der Stadt Kiel, 1888. 

3 Lepeschkin. Zur Kenntnis der Erblichkeit bei den einzelnen Organismen usw. 
Centrabl. f. Bakteriologie usw. II. Division. 1904, Vol. XII. Nos. 22-24. 



i8 

// dependence on 'the constitution of the nutritive substrata may he 
proved for parasites, naturally the strongest agent in combalting them is the 
removal of the favorable nutritive substratum and its alteration into one un- 
favorable for the special parasite. 

Since cultivated plants, by the fact of their division into susceptible and 
resistent varieties, demonstrate that there is a possibility of altering the nutri- 
tive substratum produced by living plants, the production of such resist oil 
individuals through cultivation is the first aim of our work, in regard to 
overcoming parasitic diseases. It is more effective than the present method 
of fighting parasites locally or preventing their attacks, a method which was 
deduced from a narrow point of view. At most this may be carried through 
effectively for small centres of disease but for mechanical reasons is im- 
practicable for general use. From this point of view parasitism is not such 
a great menace as it has been represented to be. 

If parasitism is a definite nutritive form of certain groups of organisms 
which has become necessary in the natural development of the living being, 
it must have its stage of equilibrium in the sphere of nature. Arrangements 
must exist which counterbalance parasitism. It must be possible to hinder 
its effectiveness by factors simultaneously effective, for otherwise the nutri- 
tive organisms could no longer exist. This counterbalance is found in 
the very definite, often narrowly restricted environment which determines 
the existence of the parasite. That condition of a living creature which we 
are accustomed to term "healthy," without being able as yet to define it, is 
one such restricting limit which the parasite under normal conditions is not 
able to overcome. For, since the defenders of the extreme theory have 
represented such parasitic micro-organisms as dangerous which are con- 
stantly present everywhere saprophytically and as yet have not killed the host 
plants as a whole, these plants must thus possess some protective devices in 
their normal development, which are repeated in the same sense from gene- 
ration to generation. We constantly find occurring as such, unbroken de- 
posits of wax and cork, definite acidity of the cell content etc. 

That we now find more and more adherents to our theory is proved by 
the statements of one of our most important students of parasitism, Met- 
schnikoff^ of the Pasteur Institute. After giving a number of examples 
to show that the production of the parasitic disease is conditioned by 
tzuo causes, first, the parasite and secondly, susceptibility of the organisms, 
he says, (page 7) "if these internal conditions are powerless to arrest the 
development of the excitor of a disease, the disease is produced. If, how- 
ever, the organism firmly resists the development of the bacteria, it is pro- 
tected and thus proves itself immune." (Page 6) "One can no longer be of 
the opinion that, every time an excitor of disease penetrates a susceptible 
organism, the presence of the same inevitably calls forth this specific dis- 
eased condition. Loffler's discovery of the diphtheria Bacillus in the pharynx 

1 Immunitat bei Infektionskrankheiten by Elias Metschnikoff, Professor of the 
Pasteur Institute in Paris. Authorized Translation bv Dr. .Julius Meyer. Jena, 
Gustav Fischer, 1902. 



19 

of healthy children has been repeatedly substantiated since that time and yet 
it is impossible to doubt the etiological significance of this bacillus for diph- 
theria. On the other hand it has been proved that Koch's Vibrio, although 
the real inciter of Asiatic cholera, nevertheless, occurs in the digestive system 
of healthy people." 

The healthy organism thus possesses a natural immunity and any distur- 
bance of this aids the possible parasitic attack. 

5. Epidemics. 

If we can define endemics as a local malady, whose production is con- 
nected with definite conditions, narrowly limited locally, then epidemic may 
be called a community malady. The expression "malady" indicates the mul- 
tiplicity of the diseased individuals in contrast to isolated cases of disease. 
Epidemic thus describes that condition in which numerous individuals suc- 
cumb to a given form of disease, developing over large territories. 

If an epidemic breaks out, conditions must be present which disturb the 
functions of the organism in numerous individuals so strongly that their 
lives are either threatened with a premature end or are finally brought to 
this end. This disturbance arises from external causes. If these causes are 
parasitic organisms, their existence, as was shown in the preceding chapter, 
is dependent on the factors of growth favorable to their extensive increase. 
Among these factors belongs the breaking down of the immunity of the 
nutritive organism. 

Even with the assumption that a parasite not indigenous to the countries 
which suffer from the disease might have caused the epidemic by its incur- 
sion, this circumstance in no way changes the fact that the factors of grozvth 
already existing are determinative for the production of the epidemic. For. 
whatever may wander into the country, be it animal, fungus or bacterium, 
this incursion would not produce an epidemic, if the newcomer found no 
opportunity for great increase and wide distribution. For example, who 
does not remember very efifective representations of the importation of the 
Colorado beetle as the destroyer of our potato crop, or the extensive intro- 
duction of the wSan Jose scale as the destroyer of our fruit trees? Initiated 
persons know how often embargo regulations and compulsory disinfection 
have advanced protection against the importation of parasitic fungi ("White 
Rot of the Grape" etc.) and they have partially succeeded in getting it. 

Experience has taught that no theoretically imagined but practically im- 
possible complete destruction or quarantine of such parasites has possibly 
protected us from epidemics but the circumstance that they did not find the 
necessary climate and soil for their increase. Conveisely, the Phylloxera 
plague should be remembered wdiich, despite all human endeavor and the 
spending of many millions, became more and more widespread. The 
Phylloxera finds, even in Europe, sufficiently favorable conditions for exis- 
tence and on this account defies such means for fighting it as embargo, dis- 
infection, processes of extermination etc. Upon consideration, it becomes 



20 

gradually clearer that small living creatures, in fact, the smallest which are 
introduced by means of articles of commerce or can be easily distributed by 
dust and wind, may be kept out of small enclosed places but not away from 
extensive open localities, and that one proceeds better by presupposing the 
possibilities of a widespread distribution of such organisms although real 
danger is to be recognized only if an easy capacity for its increase has been 
proved. If now in all parasitic incursions, not the presence of the parasite 
but the conditions favoring its spread are proved decisive for the production 
of the epidemic, then a change in these conditions is the best means for com- 
batting them. 

In regard to measures for its suppression and prevention, however, the 
epidemic furnishes special pointers in that, when it occurs over extensive 
areas, it excludes as causes all the factors which vary from one another in 
the dififerent diseased districts. For, since the malady attacks large plan- 
tations despite the variations in such factors as, for instance, situation, com- 
position of the soil, agricultural methods etc., these factors cannot be the 
cause. Rather the cause should be sought in those influences which are the 
same throughout the whole country. Actually, this can only be the climate. 
On the other hand, in endemic diseases, conditions of the soil usually act de- 
cisively. They are to be considered either direct causes of disease since, 
through unfavorable chemical or physical pculiarities they permanently dis- 
turb the functions of the plants, or they act indirectly, favoring the increase 
of the parasites and the strength of their attacks. In this, as a rule, they 
suppress at the same time the growth energy of the host plant. Soil damp- 
ness is the condition most favoring this. When the capacity of thick, heavy 
soils for retaining water is very great on the level or in hollows, an accumu- 
lation usually occurs which finds no outlet and produces a deficiency of oxy- 
gen, with an excess of carbon dioxid. The plants indicate this functional 
disturbance by a change in the chlorophyll apparatus. The leaves, gradually 
turning yellow, form a suitable growing medium for certain groups of fungi. 
In all endemics and epidemics a simultaneous sickening of a great num- 
ber of individuals indicates a considerable period of preparation leading up 
to the actual outbreak of the malady. 

For, according to our conception of all the phenomena of life as dynamic 
processes, each case of disease may be characterized as the immediate or in- 
direct result of mechanical disturbances exercised by the separate factors of 
growth on the composition and function of the substance. The life of a cell 
is a constant struggle between the oscillatory forms momentarily present in 
the unstable organic compounds and the disturbances constantly exercised 
upon them by the factors of growth. 

A change in the substance and with it one in its function appear at 
once if the disturbance in one factor of growth is so strong that it is able to 
change the form of oscillation existing up to that time. So long as the dis- 
turbances as a whole have the effect of contributing to the development of 
the organism as a whole, that is, the vegetable individual, the plant remains 



21 

within the latitude of health. Disease follows if the cell or the cell complex 
is so changed that ultimately the whole structure suffers. 

Now, however, the fact, always confirmable by examples, that certain 
cultivated varieties show a tendency to disease not shown by others under 
similar conditions of growtli, furnishes us proof that in the different individ- 
uals the organic substance may oppose a differing amount of resistance to 
the same attacks. This would mean that more attacks are necessary for one 
individual than for another in order to carry it out of the latitude of health. 
If, in an epidemic, only large numbers of individuals always suddenly become 
sick, besides the especially susceptible ones there must also be others among 
them for which a greater number of attacks and therefore a longer period 
of action is necessary, in order that they may become sick. Therefore a 
longer period of the influences producing the disease must have led up to 
the outbreak of the epidemic and these influences are to be seen in the atmos- 
pheric factors. 

Therefore, according to our theor}', each epidemic is, so to speak, the 
explosion of a charge which had been slowly accumulating for some time. 
Its cause therefore is not to be sought, at least exclusively, in the existing 
factors of growth present at the moment but in the accumulation of attacks 
which for some time previously have been effective in the same way. In 
parasitic epidemics the extensive occurrence of the micro-organism in no 
way represents the first stage of the phenomenon but is a final effect of long 
preparation. This preparation consists on the one hand in .the gradual pro- 
duction of life conditions favorable for the enormous increase of the micro- 
organisms, on the other hand, in the gradual weakening of some functions 
of the host which we believe are always connected with tliis and a correlative 
increase of other functions. 

If, for example, we study the best known fungous epidemic, potato 
blight, observation shows that a period of warm, dull, sultry days usually 
precedes the outbreak. The fungus Phytophthora infestans is always 
present. Its astonishingly rapid increase, however, takes place out of doors 
only if abundant atmospheric precipitation and a warm motionless air con- 
tinuously favor the production and the scattering of the swarm spores. Dur- 
ing weather of this kind the potato plant develops a greater amount of sugar, 
a more rapid stem growth and a great number of young leaves ; that is, it 
produces an especially susceptible environment for the development of the 
fungus which scorns organs that have become old. In this way we find that 
whole fields may become diseased in a few days. 

On the other hand we do not find the Pytophthora epidemic if the same 
amount of precipitation occurs in the same space of time but in cold weather. 
The epidemic cannot develop if, with increased warmth and a clouded sky, 
persistent strong winds keep blowing. A similar relation is shown in rust 
epidemics of grains. Like the majority of fungi the grain rusts loye con- 
tinuous moisture. Yet by no means do we always have rust epidemics in wet 
years, although there might be scarcely one grain field in which the rusts 



22 

would not be present every year. The epidemic develops at the time when 
the leaves are young and only during periods of warm days with frequent 
even if almost unappreciable showers which make possible a longer retention 
of moisture among the plants. Cold, wet summers generally prevent the 
development of rust epidemics. Similar conditions may be observed in 
bacterial epidemics. 

Therefore, epidemics are forms of disease which mature only because of 
far reaching factors. Only certain weather combinations of longer duration 
may be considered as the initial cause. Naturally the intensity of the epi- 
demic will vary locally because local factors will produce special favorable 
conditions. In this way is explained the occurrence of centres in which the 
malady appears first and disappears last, in case not all the individuals are 
killed in a short time. In this way is explained further the retrogression of 
epidemics into endemics ; that is, into narrowly confined centres of disease. 
Among the epidemics produced by animal parasites, those caused by grain 
flies are the most abundant with us. They usually take place during periods 
of continued warm, dry weather after the winter conditions have been favor- 
able for the individual grain flies which in some regions are always present. 
So far as statistics now go, preferred centres and points of departure may 
often be determined for this plague-like distribution. Thus, for example, 
the province Posen is proved to be especially favorable soil for grain flies. 
From Posen as a centre an epidemic usually radiates towards Brandenburg, 
Pomerania and- West Prussia. The whole Eastern part of Germany suffers 
more from injuries due to flies than does the Western part. North Western 
Europe is usually visited more frequently and intensely than South Western 
and South Eastern Europe. 

According to the point of view here developed any treatment of the 
epidemics by fighting the symptoms as they appear must ofifer the least pros- 
pect of success, because these are only the result of initial stages which 
existed long before. If the parasites arc present in enormous quantities the 
desire to kill the micro-organisms is seen to be a vain one since no insecticide 
or fungicide can even approximately reach the main mass and still less cause 
its death. Thus as the pestilences are induced by general factors acting uni- 
versally, they must be combatted by broad means which undo the life con- 
ditions of the parasite and change the constitution of the host, that is, the 
functional direction. If, for example, long wet periods permit the bacterial 
rot of potato, which we call "zvet rot," to appear in epidemic proportions, 
any other means than increased ventilation of the soil can scarcely be used 
successfully. So far as specific anaerobic bacteria are concerned, the factor 
favorable to growth (lack of oxygen with excess of carbon dioxid) is re- 
moved by an increase of oxygen and also by the decrease for them, as well 
as for other bacteria, of the condition fundamental to their abundant in- 
crease, an abundance of water. Nature generally works in this way. If, 
after the rainy periods, dry, windy weather continues for some time so that 
the soil dries and the air circulates freely, the progress of the disease comes 



naturally to a standstill. The recommendation of every regulation for the 
prevention of infection by the removal of infected potatoes from the field, or 
by deep subsoil cultivation, or the burning of diseased straw in grain epi- 
demics, we consider to be a work with insignificant results as contrasted with 
the effect of changed life conditions for the parasite. The amount of in- 
fected material in extensive districts does not come under consideration at 
all. At times in the case of damp rot, soil bacteria co-operate and form a 
dense condition of the soil. If atmospheric influences make themselves so 
felt in certain soils that certain bacterial groups are able to attack potatoes 
or other fruits of the field, the number of the causative agents of the disease 
originally present is almost of no significance. 

The last named examples of parasitic epidemics due to such micro- 
organisms as may be assumed to be constantly present in the soil or the air, 
make clear to us, however, how little prospect of success is ofl^ered for com- 
batting an epidemic once it has broken out. A greater protection for our 
cultivated plants lies in preventive methods. Such a preventive process in 
epidemics, aside from the formation of an universal plant hygiene, can, how- 
ever, be induced by the drawing up of a chart of pestilences; that is, a sum- 
mary of plague centres for each individual epidemic. In the correspondence 
of certain characteristics for a number of plague centres, single factors are 
especially distinguished as fundamental for the production of an epidemic ; 
for example, dryness in light soils is shown to be favorable for fly epi- 
demics of grain or for the heart-rot of sugar beets etc. Having thus deter- 
mined weather and soil combinations dangerous for each individual epidemic 
one can make one's attack prophylactically by means of cultural regulations 
as soon as the threatening combination of conditions continues for some time. 
Direct means which kill the parasites, such as sprinkling with copper sulfate 
or dusting with sulfur, will then act only as hinderances to the epidemics if 
used preventively. 



6. Artificial Immuniz,ation and Internal Therapy. 

It is quite natural that in phytopathology the same course of ideas has 
developed as in animal patholog}^ and accordingly it is not strange that there 
has gradually become evident a theory of immunizing plants artificially ; i. e., 
of so changing their bodily composition that the parasites will no longer find 
the nutritive soil necessary for colonization, for their wider distribution. 

There already exist several works along this line in which, following in 
part serum therapy, use is made of immunifying substances obtained from 
the parasite itself, and again v/here mineral salts are used. Along the former 
line belong Beauverie's^ investigations with Botrytis cinerea and those 
of Ray- with very different kinds of parasites. The latter obtained 



1 Beauverie, J., Essai d'immunisation des vegetaux contre les maladies crypto- 
g-amiques. Compt. rend. Paris 1901. 11, p. 107. 

- Ray, J., Cultures et formes attenuees des maladies cryptogamiques. Compt. 
rend. Paris 1901. II, p. 307. 



24 

the result that parasitic organisms may be influenced in artificial cultures 
by the nutritive medium used. In this their virulence is proved always to 
be less than it is under natural conditions. By leeching the cultures, fluids 
may be obtained which may be used for the immunization of the host plants 
against the organism concerned. The author concludes further that the in- 
fected plants are actually cultures of the parasites concerned. In this 
maceration and extraction of the diseased plant parts must furnish fluids 
which would exercise an efli^ect similar to that of the parasite itself. When 
modified by increased temperature, these fluids can be used for immunization. 

E. MarchaF should be especially mentioned as a representative 
of the other line of immunization experiments. He worked with mineral 
substances, some of which were nutritive, while others should be considered 
poisonous. He sowed lettuce in Sachs' nutrient solution with the addition 
of substances which kill fungi. The young seedlings, after the development 
of the first two or three leaves, were infected with the zoo-conidia of Bremia 
Lactucac and then kept in a moist atmosphere. The plants, not rendered 
immune by the substances in the nutrient solution which would kill fungi, 
were at once attacked. Of the salts used, the addition of from three to four 
ten-thousandths copper sulfate to the nutrient solution was clearly proved to 
increase the resistance. The addition of i-ioooo copper sulfate no longer 
showed any immunizing effect whatever. Manganese sulfate acted less com- 
pletely; ferrous sulfate had no effect at all. Calcium salts also (up to 2-100) 
could increase the resistance while nitrates and also, curiously enough, phos- 
phates lessened it. 

The idea of increasing each individual's susceptibility to vegetable para- 
sites by changing the cell sap through the addition of foreign substances was 
also taken up by zoologists who preceded in accordance with the discovery 
that parasitic animals, for instance, scale, seek out weakened plants especially. 

Now, however, was associated with this the thought, that universal con- 
ditions of weakness in cases of constitutional disease as well as conditions of 
susceptibility to parasitic attack could be healed by supplying salts of some 
definite kind to the plant body extra-radically. This taking up of substances 
otherwise than through the roots was called "Internal Therapy'' and was 
developed methodically. 

In 1894, I. Schewyrjov- published an article on "the impregna- 
tion of the wood in living trees with solutions of coloring matter" (Ueber die 
Durchtrankung des Holzes lebender Baume mit Farbstofflosungen"). In 
it he describes the apparatus which he constructed for this purpose which we 
will call nutrition tube and nutrition basin. The tube is of steel, pointed at 
one end, which is driven into the bark, while the other end is closed by a 
cork, through which passes a gimlet. The tube is filled with the experimental 
liquid, through special openings, by means of a rubber tube. Then the gimlet 



1 Marchal, E. De rimmunisation de la laitue contre le meunier. Compt. rend. 
1902. CXXXV, p. 1067. 

s Schewyrjov Iwan, Berichtigung usw. Zeitschrift flir Pflanzenkrankheiten. 
1904. p. 70. 



25 

is bored slowly down into the wood to the desired depth so that the liquid 
but no air can penetrate into the canal thus formed by the gimlet. The 
author who had constructed other apparatus also mentioned Hartig's ex- 
periments which had the disadvantage of letting air penetrate into the 
wound. He then began experiments on the healing of chlorosis which were 
carried out in 1895-6 and in 1901, by garden owners in the Crimea. 

Later Mokrzecki^ published a number of successful experiments 
on the healing of chlorosis in fruit trees carried out according to the above 
method, in which he also pointed out that the scale had disappeared from the 
healed branches. He, as well as Schewyrjov, built great hope on this pro-> 
cess, not only for the prevention of constitutional disturbances in nutrition 
but also especially for the expulsion of parasitic organisms. 

My personal attitude toward this question is much cooler and I think 
that the effectiveness of the methods will be very limited. According to my 
experiments on the introduction of poisonous solutions into the trunk, the 
effect usually remains local but in the most successful cases radiates grad- 
ually from the_ point of introduction to a number of branches and to a con- 
siderable distance into the trunk. The constitution of the plant, conditioned 
by root nutrition, was not changed by this. I found in my experiments with 
oxalic acid that gum was produced on a number of cherry tree branches 
which later partially died. However, the production of gum did not progress 
further the following year and the trees, moreover, made a healthy growth. 
Like this poisonous solution, each nutritive mixture or healing serum remains 
limited within narrow boundaries and, as in the most favorable case, only 
temporarily exercises any beneficial influence. The physiological direction 
of the work of the whole plant will not be changed permanently. 



7. Predisposition. 

We term "predispositivon" that condition of certain individuals which 
renders them more easily and quickly susceptible to any cause of disease than 
are other individuals of the same kind. 

That such cases exist is proved by daily discoveries as to the quantitative 
growth of cultivated plants. These discoveries have already found expression 
in the common use of the terms tender and hardy varieties and individuals 
which have been made less resistant. Observations show that not only diifer- 
ent cultural varieties of the same species but even single individuals of the 
same variety possess a varying power of resistance to weather extremes, as, 
for example, cold and heat, or to parasitic attack. Li the latter connection, 
it suffices to mention that practical workers as well as scientific investigators 
have now set themselves the task of breeding more resistant varieties. 

At present we are only in a position to indicate the direction in which a 
greater individual inclination to succumb to any parasitic attack may be pro- 



1 Mokrzecki, S. A. Ueber die innere Therapie der Pflanzen. Zeitschr. f. Pflan- 
zenkrankheiten. 1903. p. 257. 



26 

duced. In the previous divisions we have considered investigations showing 
that different groups of substances produced in the plant cells, as, for in- 
stance, sugar, act attractively for certain fungi in definite concentrations and 
repellantly in others. The number of these groups of substances is deter- 
mined by very different factors, as will be shown more thoroughly in the next 
chapter. This metabolism will be found favorable for the nutrition of the 
parasite or unsuitable for it, according to the quantity produced. 

In order to cite at least one example in this connection, we will refer to 
the investigation of Viala and Pacott^ on the black rot of the grape. 
The cultures, undertaken wij:h the fungus Guignardia Bidzvellii which pro- 
duces the disease, determined that the development of the fungus is depen- 
dent primarily on the sugar content of the nutrient substratum and its organic 
salts. Only young leaves were affected. They contained 1.75 per cent, tar- 
taric acid and 4.3 per cent, glucose, while the old leaves showed only traces 
of these substances. The berries were susceptible from the time they began 
to swell and this susceptibility continued up to the beginning of the ripening 
stage. During this time they contained 32 to 24 per cent, of acid and 11 to 
56 per cent, of sugar. During ripening the acid content falls from 9 to 2 per 
cent., but the sugar content increases so greatly that the fungus can no longer 
attack the berries. The conditions for the white rot fungus, however, are 
exactly reversed. By this relation is explained the strikingly different resis- 
tant capacity of different kinds of grapes. In the same way is explained the 
circumstance that black rot epidemics generally occur in summer after 
periods of cold weather with subsequent light rainfall. At this time the acid 
content is especially large and the formation of sugar scanty. Similar fluct- 
uations in the concentration of the cell sap combined with the phenomena of 
perforation of the membrane, the varying processes of tension in rhe tissues 
and other mechanical changes also in the plants cause a state of greater sus- 
ceptibility to weather extremes. The more recent investigation is endeavor- 
ing to find more macroscopic and microscopic characteristics also demarking 
the stages of susceptibility to injurious parasitic attacks. 

The conditions pictured in the preceding example of the increased tend- 
ency of the grape to become susceptible to the black rot fungi are entirely 
normal developmental phases which are influenced by the weather. On this 
account we may speak of such states as normal predisposition. In contrast 
with these we should distinguish as abnormal predisposition the case in which 
the plant or one of its organs has fallen into a condition of weakness or of 
disease from other influences and in this conception of one cause of disease 
is first given the desired point of attack. As an example, we will call attention 
to the infection of leaves affected with honey dew by the black fungi, to the 
attacks of the so-called parasites of weakness and the migration of wood- 
destroying fungi from wounded surfaces. 



1 Viala, p., et Pacottet, Sur la culture du black rot. Compt. rend. Paris 1904. 
Vol. CXXXVIII, p. 306. 



27 

8. Predisposition and Immunity. 

In an earlier part we have pointed out that our theory as to the produc- 
tion of parasitic diseases has obtained support from the most renowned in- 
vestigators. Metschnikoff\ who, as professor in the Pasteur Institute 
for infectious diseases, may be incontestibly considered as an exact con- 
noisseur of pathogenic micro-organisms, expresses himself as follows, 
"Exact bacterialogical mvestigations have led to the knowledge that, in the 
abundant bacterial flora harbored by the healthy human body, representa- 
tives of pathogenic bacterial species may also be found. Aside from the 
Bacillus of diphtheria and the Vibrio of cholera which so often have been 
proved to be fully virulent in perfectly healthy human luMngs, it has been 
shown that certain pathogenic micro-organisms, the Pneumococci, the Sta- 
phylococci, Streptococci and Colibacilli, are present regularly or almost con- 
stantly in the microbe flora of healthy persons. 

This discovery has of necessity led to the conclusion that besides the 
excitor of the disease, still a second cause of infectious diseases must exist, 
namely, a predisposition or a lack of immunity. An individual which harbors 
one of the species of pathogenic bacteria above-named would be resistant 
either permanently or for the time being. But as soon as this immunity dis- 
appears, the excitor of the disease becomes uppermost and produces the 
specific disease." 

In regard to the immunity of plants, Metschnikofif calls attention to the 
investigations of de Bary- on Botrytis, which we have already men- 
tioned. The mycelium of this fungus penetrates the cell walls by giving off 
a fluid "which contains a digestive ferment and the oxalic acid necessary for 
this ferment. De Bary could prove the presence of this kind of toxin by the 
maceration of the mycelium of Sclerotinia .... If the resulting fluid 
is heated to 52°C. it can no longer digest the cellulose membrane but is still 
able to cause plasmolysis .... The results of de Bary's investigations 
have been confirmed and in part completed by Laurent.'"^ 

We have repeated Metschnikoff's words in order to characterize his 
way of considering the matter. The chief factor under consideration here, 
viz., the efifectiveness of the ferment on young membranes and its ineft'ective- 
ness on older ones, gives the author reason for comparing the Botrytis dis- 
eases with the infantile diseases in human beings (measles, scarlet fever). 
In other cases the different processes of cork production, or suberization, 
found, for example, in wounds, act in a way similar to the membrane changes 
in the ageing of the cells. In regard to these, Metschnikoff, supported by the 
investigations of Massart^ points out that the organs respond difl:"er- 
ently to the traumatic stimulus according to their age. Young leaves of 
Clivia, for example, re-act by forming callus, older ones simply close the 

1 Metschnikoff, Immunitat bei Infectionskrankheiten. Jena, 1902, p. 6. 

2 De Bary Bot. Zeit. 1866. 

3 Laurent, Annal. de I'lnstitut Pasteur. Vol. XIII, p. 44. 

4 Massart, La Cicatrisation ciiez les plantes. Brlissel 1897. 



28 

wound by means of a deposition of cork. Further protective means are oils, 
resin, balsams, milky juices and gums exuding from injuries. 

Metschnikoff thoroughly treats of Laurent's^ studies which are 
mentioned in connection with other bacteria in the second volume of this, 
work. At this point, however, we will emphasize especially the immunity 
precautions against bacterial attacks. The species of the Colibacillus, with 
which Laurent worked, secretes a ferment dissolving the cellulose of the 
potato tuber and produces also sap with alkaline reaction, the presence of 
which is necessary for the process of assimilation on the part of the bacteria. 
Now, to be sure, Bacillus Coli communis is naturally not a plant parasite but 
it can be changed into one. This happens when it is first cultivated on po- 
tatoes whose resistance has been weakened by having been dipped into alka- 
hne solutions As a result of such cultivation the bacillus can act as a plant 
parasite when carried over to the same species of potato. The struggle be- 
tween the Colibacillus and the potato depends therefore really on the chemi- 
cal action of the alkaline secretion of the bacillus on the acid cell sap of the 
potato. After fertilization with potassium salts and phosphates, carrots and 
potatoes resist the bacillus. On the other hand, a phosphate fertilization 
showed in (Topinambur) that this plant then became more susceptible to the 
Botrytis form of Sclerotinia Libertinia. 

Just as clearly by strong nitrogen fertilization potatoes are made less re- 
sistant to wet rot. According to our observations abundant fertilizing with 
nitrates, ammonia salts or stable manure, causes even the most resistant 
species to succumb to the potato rot. Laurent explains the difference in the 
action of parasites under the same method of fertilizing by the fact that with 
bacteria the secreted ferment can attack the cell membrane only in alkaline 
juices or weakly acid ones. An increased acidity of the cell sap, incited by 
the formation of acid salts resulting from phosphate fertilization, renders 
the plants immune to this fission fungus. I obtained the same results for 
phosphoric acid by fertilization experiments on sugar beets, in which the 
Bacillus betae was widely disseminated and had produced the bacterial for- 
mation of gum or tail rot. The rapid increase of bacteriosis with the abun- 
dant use of fertilizers which contain nitrogen might be explained in this 
way: — that the acid of the cell sap is thereby decreased. According to de 
Bary, the conditions for Sclerotinia are exactly reversed. Their ferment 
dissolves the cell wall only in an acid fluid. Most mycelial fungi act 
similarly. 

If, by a change of constitution of the cell sap, sometimes a factor of im- 
munity presents itself and, at other times, a condition predisposing to para- 
sitic disease, we are referred by Metschnikoff (1. c. p. 39) to a further pro- 
cess. He cites the investigations of van Rysselberghe- who found, 
especially in the epidermal cells of Tradescantia that if these cells were 



1 Laurent, Recherches experimentales sur les maladies des plantes. Annal. 
de rinst. Pasteur. Cit. Zeitscher. f. Pflanzenkr. 1900, p. 29. 

2 Osmotische Reaktion der I'flanzenzellen. Memoires couronnes de I'Academie 
r. d. Belgique. Briissel 1899. 



29 

brought into a more concentrated solution than was normal to them, they 
showed an increase of intra-cellular pressure. iT the experiment was re- 
versed, the pressure decreased. These changes in osmotic pressure are 
caused by the difference in concentration of the cell sap which may again be 
considered as a result of chemical changes. If the cell comes in contact with 
a solution too highly concentrated, it forms oxalic acid which acts strongly 
osmotically. With Tradescantia, van Rysselberghe proved the presence of 
malic acid in the normal sap and only in rare cases any traces of oxalic acid. 
After the plant had been kept some days in strongly concentrated cane sugar 
solution, oxalic acid was found in clearly appreciable amounts. The plant 
gradually adjusts itself to the higher concentration of this medium, produc- 
ing oxalic acid in order to increase the pressure of the cell sap. The acid is 
supposed to be formed at the expense of grape sugar. The increased acid 
content will act as a protective means against bacterial attacks. It is also 
suggested by some investigators as a protective weapon against the attacks 
of snails and leaf lice. 

Experiments with Tradescantia made in the opposite direction seem to 
me to be very significant. If tissues from this plant were taken from the 
highly concentrated solution and put into some strongly diluted solution, 
precipitates of calcium oxid crystals were observed in the cell sap, thereby 
initiating a decrease of osmotic pressure. When the plant was put back into 
a stronger solution the oxalic crystals were seen to re-dissolve and result in 
a new formation of acid. I found that part of the calcium oxalate crystals 
disappeared during the sprouting of potato tubers which also may well be 
ascribed to the increased formation of acid. 

Pfeffer^ also takes up this automatic regulation of the acid con- 
tent since he calls attention to the frequent production of turgidity through 
the organic acids combined with bases. Since this remains constant during 
and after growth, the formation of acid must be hastened quantitatively in 
correspondence with the volume increase of the cell and the dilution of the 
cell sap thereby produced. Each unusual increase of turgor, as, for example 
in the effort to overcome an opposing higher concentration, will be connected 
with a corresponding increase in the acid production. Conversely, for exam- 
ple in the Crassulaceae, the decrease of the acid content has been proved 
with an increase in temperature and by illumination. In this same sense the 
experiments made by Charabot and Hebert- have succeeded. In the shade, 
the quantity of combined organic acid increases very considerably. 
The free volatile acids also increase. These are found in greater amounts in 
etiolated plants than in others. The suppression of the inflorescences in- 
creases in the leaves at the expense of the other organs. 

In considering predisposition and immunity, we have brought forward 
the sugar content in addition to the examples of acid content. To what 



1 Pflanzenphysiologie, II Edition, Vol. I, p. 487. 

- Charabot, Eug-., et Hebert, Recherches sur 1' acidite veg-etale. Conipt. rend, 
hebd. 1904. CXXXVIII, 1714. 



30 

fluctuation this is exposed by changes in temperature is best seen in Fischer's^ 
investigations cited by Pfeffer-. In the so-called starch trees, like the linden 
and birch, it is found that starch is formed in the bark within a few 
hours after the branches have been brought into a warm room from a 
winter temperature. In the cold, sugar is again produced from this starch. 
This conversion may be repeatedly produced and this kind of sugar forma- 
tion seems to appear in many plants with a lowering of the temper- 
ature. If now-, for any reason w^hatever, the sugar formed from the 
starch is conducted away from the organ the whole tissue may be im- 
poverished. Pfeffer furnishes proof of this by the experiments carried 
out in his institution by Hansteen^ and Puriewitsch*. By a con- 
tinued removal of the sugar by diosmosis, it was possible to cause an ejection 
of starch from the isolated endosperm of grasses as well as the cotyledons 
of Phaseolus which had been cut ofY from the plant and a giving off of the 
glucose from the separate scales of the bulbs of Alliiim Ccpa. If only a 
little water was present into which the sugar could pass from the organs the 
ejection came to a standstill because a two to three per cent, sugar solution 
inhibits the conversion of the starch. Therefore, either a good deal of w^ater 
must be present or some other means for the removal of the starch if the 
ejection should be completed. Con^ersely, a refilling of the organs with 
starch could be determined if a still more concentrated solution were used. 

These examples may suffice to show how in the plant body all the me- 
tabolic processes and all the resulting constructive processes succumb under 
constant quantitative changes which radiate in all directions from the first 
form of attack of the factor causing the change. Each change occurring 
locally is a disturbance in the condition of equilibrium existing up to that 
time in the molecular organization. If the disturbance is completed in one 
cell it must, so far as diffusible substances are concerned, be continued in the 
neighboring ones as are all dynamic processes. 

Each place in which a new structure is formed becomes a centre of 
consumption. The supply of food to this new structure leads to a reduction 
in other parts. Each local increase in photosynthesis exerts its influence on 
the immediate surroundings not concerned in this process. The different 
factors of growth now act uninterruptedly on the plant body and disturb the 
momentary equilibrium, first in this direction, then in that. We have there- 
fore a continued fluctuation in all life processes which is increased still more 
by the capacity for reaction peculiar to the individual, for we dare not forget 
that in restoring the disturbed equilibrium the organism must endeavor to 
increase its production of different substances. If, for example, there sets 
in an increase of the basic compounds conditioned by nutrition, an increased 
acid content will have to be brought about and conversely. And within the 
constant fluctuations which are a necessarv result lies the condition which 



1 Fischer, A., Jahrb. f. wiss. Bot. 1891. Vol. 22. 

2 Physiology I, p. 514. 

3 Hansteen, Flora, 1894. Supplement. 

4 Puriewitsch, Ber. d. Deutsch. bot. Ges. 1896. p. 207. 



31 

we term normal predisposition. Thus the same condition which represents 
a state of predisposition toward a definite cause of disease can act as a state 
of immunity to some other cause of disease. Proofs of this are offered by 
the examples above cited of the hyperacidity of the cell sap which has been 
shown to give immunity to certain bacterial attacks and predisposition to 
those of fungi. In the increased sugar content, which is connected with the 
influence of the acid in increasing the turgidity, we recognize a condition 
predisposing to injuries arising from frost and, on the other hand, a pre- 
cautionary means against the disturbing action of drought. 

In the very natural development of the organism, therefore, we con- 
stantly face conditions of predisposition and immunity. These are present in 
varying degrees in each indi\'idual since each organism has special nutritive 
relations and utilizes differently the same factors of growth. This explains 
the phenomenon that different individuals in the midst of a community of the 
same species become sick or conversely, in the midst of a centre of disease, 
remain healthy^. 



9. Inheritance of Diseases and of Predisposition. 

In the last four decades further experiments have been made by many 
important investigators to explain theoretically the nature of heredity. In 
this, special consideration was given to the most juvenile condition — the 
embryonic plasma — as a transmitter of the capacity for inheritance and the 
substance which might be indicated as the chief transmitter of inheritance 
was sought in part in the cell nucleus. 

The above-mentioned hypotheses of biologists were drawn up to explain 
especially the repetition of the formative processes in the successive genera- 
tions of the organism. We will call attention only to Darwin's "gemmules," 
Haeckel's "plastidules," Weismann's "germ plasm" as an "heredity plasm," 
Nageli's "idio-plasm," de Vries' "pangene," etc. 



1 The parasitic theory as generally accepted at present either still needs 
an explanation of these facts or is restricted to the theory of resistance. The 
different capacity for resistance to atmospheric extremes and other non-parasitic 
influences has remained unconsidered. Thus Alfred Fischer* observes "Individual 
variations indeed occur often enough even in man; a personal immunity of an 
inexplicable kind seems to exist which in part falls under the conception of predis- 
position. Even with ag-e natural immunity varies as shown by infantile diseases. 
The question may be left undiscussed as to whether even these may not be con- 
sidered as immunizing: diseases which are said to prepare tlie youthful mortal for 
an existence surrounded by bacteria and to fortify him.'' 

On the other hand, Alfred Wolff** explains "In all essentials the natural power 
of resistance to toxins advances in proportion to the organ's capacity to hold the 
molecules of the poison and to prevent their action on the brain. Thus only quali- 
tative and no quantitative differences exist between apparently so diametrically 
opposed phenomena of an innate non-susceptibility and a high grade of susceptibil- 
ity in individual animal bodies. These differences lie only in the different capacity 
of the organs in different animal species for the formation of toxin and an eventual 
neutralization." 

♦Fischer, A., Vorlesungen uber Bakterien. 2. Ed. p. 347, Jena, Gustav Fischer, 
1903. 

**Alfred Wolff, Ueber Grundgesetze der Immunitat, Centralbl. f. Bakteriologie, 
Parasitenkunde usw. Sec. I. Original. Vol. XXXVII. Part 3, p. 701, 1904. 



2>2 

According to our theory there is needed for the explanation of the pro- 
cesses of inheritance, neither any special locality such as the embryonic cells, 
nor any special cell or plasm germ or inheritance mass or any ancestral plasm, 
for inheritance is a "mechanical must" a necessary universally present me- 
chanical result of the structure of the organic substance. As soon as the 
organic substance, like the inorganic, is considered as an atomic union which 
retains its character and therefore its specific peculiarities, since the atoms 
in the molecules exist in definite arrangements and fluctuation, then this sub- 
stance presents the stage of equilibrium of definite forms of motion. If one 
cannot define the countless combinations of molecular fluctuations and can- 
not construct the distention and other mechanical results arising from the 
dififerent arrangement, one may yet characterize each organic structure as 
the result of a sum of very definite coml)inations of molecular motions which 
are conditioned by each other. Accordingly the cytoplasm of the pear is a 
plasma whose different micellae show in general the molecular fluctuation 
forms of the plasmatic substances but still possess specific relations of fluct- 
uation and arrangement which distinguish them from similarly located 
micellae of the apple cytoplasm. Therefore, in each smallest particle in each 
biogen of any organic indiz'idtial ivhatever, an individual character may be 
found which must remain constant as an expression of the sum of definite 
forms of motion resulting from the law of inertia. 

This constancy is a mechanical necessity ; — for every motion continues 
in its existing form as long as it is not m.odified by another demonstration of 
force and each substance which is the expression and bearer of the motion 
retains this form and character until other reactions cause molecular 
changes^ If, for example, we speak of protoplasm, we must be 
conscious that we do not designate thereby a homogeneous substance with a 
fixed chemical nature, but a large group of substances containing many 
forms. The same is true for cellulose, sugar, tannic acid etc. 

The assumption of the existence of as many variations of substances as 
there are individuals loses its strangeness as soon as we remember that we 
see about us daily an equal number of variations of figures, — for, as a fact, 
no one individual resembles another absolutely. If, however, each biogen is 
a specific unit, it retains its character with the provision that no substance 
coming from without may change its molecular grouping, no matter where 
it is located in the plant body, nor whether it occurs in the form of cellulose 
or as somatic or embryonic tissue. For all these substances are indeed only 
groupings proceeding from one another. The biogens which are utilized in 
the formation of the embryo, that is, at the beginning of the new generation, 
find an expression in the new individual as in the old for the form of fluctu- 
ation which they represent. This retention of the molecular form of motion 



1 This view of the specificity of each biogen in every organism has already 
been expressed by Noll, since he states that the egg cell of a linden in its 
totality is already a linden and cannot be anything else nor become anything else. 
Noll, Beobachtungen und Betrachtungen uber embryonale Substanz. Sond. "Biolog. 
Centralblatt." Vol. XXIII, Leipzig 1003, p. 325. 



33 

in the new generation is hercdiiy. We are not in the least astonished to find 
carrot substance reproduced from carrot seed. We are also not astonished 
to find a table carrot produced from a carrot which is rich in sugar and not 
a cattle carrot rich in starch. Thus the same combinations of substances are 
transmitted which represent the characteristic peculiarities of our cultural 
varieties. If in practical agriculture we should plant side by side both of the 
above-named varieties of carrots we would have opportunity to observe that 
with the appearance of a certain degree of frost, the table carrots would 
freeze while the cattle carrots would remain uninjured. 

The susceptibility to cold of the substance of different varieties of the 
same species is the most easily observed example of the inheritance of such 
peculiarities as represent predisposition to disease. Each fruit grower can 
name varieties of fruit which are injured by frost in his orchards while 
other varieties standing nearby are not affected or injured. The same rela- 
tions are found among flowers and with grain it is a universal experience 
that, among the different varieties of wheat, for example, the square-heads 
winter-kill most easily. Tlie same variation in the resistance of differ- 
ent cultural varieties is found also in relation to other causes of disease, as, 
for example, overheating and drought, excess of water etc. A great deal 
remains to be learned of the cultural varieties and their study deserves 
greater attention than has been given to it up to the present. 

Thus cultivation has furnished us with an ornamental plant, coxcomi) 
(Cclosia cristato), which has a stem with a broad, much curled vegetative 
tip. This broad, band-like transformation of the original cylindrical stem 
(fasciafion) has become constant in the seed. Double blossoms are retained 
from one generation to another. Weak or one-sided formation of the sex- 
ual organs can become an hereditary peculiarity, as, for example, in the 
black currant or in the strawberry culture in /\lten Lande near Hamburg, c 

From such examples one sees v.diat far reaching differences from the 
usual mode of development are transmissible through the seed. Each vari- 
ation indicates a direct thrust against a previously existing peculiarity which 
is so strong that it is al)le to shatter this peculiarity permanently. The 
peculiarities of the organism possess a varying degree of stability, i. e. the 
form of motion which they represent is often disturbed by a weak thrust, 
while in other cases it can not be changed by the strongest attacks of the 
surrounding factors of growth. Among the least fixed peculiarities belong 
the colors of the blossoms, the water and sugar content and the size pro- 
portions of the organs which can vary even in the natural habitat. Hardest 
to alter or cause to vary are the relative positions of the organs and the com- 
position of the biogens, viz., the type of substance forming cabbage head or 
of a pear tree as such, and distinguishable from that of other plants. No 
peculiarity of an organism may be considered as indestructible but a num- 
ber of peculiarities will be retained from generation to generation in their 
present form because no thrust has existed up to that time of sufficient 
strength to shake them. These peculiarities, however, which are ac- 



34 

cessible for factors existing at the time may succumb to the thrust according 
to the strength of the attack and thus be changed. These changes, because 
indicative of molecular transpositions, are constant as forms of fluctuation, 
due to the law of inertia until new thrusts give a new direction to the motion. 
They are retained also in the organs which we call seeds and must accord- 
ingly be continued in the new individual and therefore must be hereditary. 
At times also, conditions contrary to the purpose of the individual, and which 
therefore initiate the shortening of the life period of the individual, such as 
a lesser firmness of the substance, will be hereditary. In this sense we will 
have to reckon with an inheritance of diseases and of conditions which make 
them especially inclined to predisposition to a disease. 

Besides the transference of such physiological peculiarities which pro- 
mote disease in the host organism from one generation to the other, the pos- 
sibility of an inheritance of parasites through the seeds of the host plant 
has recently been disputed. Erikfeson^, one of the most prominent 
investigators of rust diseases, describes a number of instances in rust of 
grain leaves which have led him to believe that with rust fungi embryonic 
developmental stages exist in which the fungi as naked plasma, Mycoplasm, 
appear united with the plasma of the host cell. Such s3mibiotic conditions 
can be present during the maturing of the seed and can exist as a dormant 
germ of the rust disease in the succeeding generation. With weather con- 
ditions favoring fungous development, the rust disease becomes apparent by 
the mycoplasmated spots transmitted by inheritance in the form then known. 
The extraordinary difficulty of the question as to the existence of parasites 
in a mycoplasmatic stage has precluded as yet any fixed decision concern- 
ing Eriksson's point of view. If the possibility of mycoplasmatic conditions 
must be admitted, we still think, however, that Eriksson's assuredly correct 
observations may have this significance since the forms described have as 
yet been found only near mature spore centres. 



10. Degeneration. 

Erom time to time, especially in practical work, it is asserted generally 
that our cultivated plants tend to degenerate, i. e. the quantity and quality 
of their crops diminish, and that certain varieties run out. The degeneration 
of such favorite cultivated forms, said to take place simultaneously in differ- 
erent localities, is often traced to senility since it is asserted that even those 
groups of forms, which we are accustomed to call sorts or varieties, like in- 
dividuals, are not able to live beyond a definite age. This point of view is 
supported especially by observations on our fruit trees, the varieties of 
which are known to be constantly propagated asexually by grafting or 
budding. Such varieties as a rule originate from one individual plant grown 



1 See Literature in "Zeitschr. f. Pflanzenkrankh." Annual numbers for 1903 
and 1904. 



35 

in a definite region, the branches of which are at once distributed as scions. 
It is now thought that all individuals produced by asexual propagation act- 
ually represent only the continuation of the tree first developed from the 
seed. Now, since each individual has its own life period, this many-headed 
individual which we call a "variety" must fall victim to death after a definite 
length of time. In this way is explained the universally simultaneous sick- 
ening and dying out of many a variety. As examples of this kind are given 
Golden Pippin and Borsdorfer, two varieties of apple, on the degeneration 
of which there developed an extensive literature in the seventies of 
the last century^. 

Other old fruit varieties (especially apple) are said to sufifer simultane- 
ously from sterility wherever grown, become cankered and die. Potato var- 
ieties, formerly widely acknowledged to be excellent, are no longer true to 
type and disappear from the market. The orange trees found formerly in 
European gardens as most vigorous old specimens become diseased every- 
where in spite of the greatest care. The celebrated orangeries at Sanssouci, 
Dresden, Cassel, Versailles etc. have vanished or are represented only by a 
few often sickly trees. Indeed, even in Italy, large plantations of lemon and 
orange trees have been attacked by diseases at present apparently incurable. 
The cause is said to be a weakness of growth which makes itself gradually 
increasingly felt, together with a diseased condition of the root. The same 
may be affirmed of grape vines and of olive trees, pomegranates, the Ericas 
(heathers) of Cape Colony, the Australian Papilionaceae and Myrtaceae, 
■which formerly, as "Javanese" plants in special conservatories, formed the 
decoration and pride of gardeners. Even in our species of grains, we have 
noticed the disappearance of the good old varieties. This is the opinion of 
the representatives of the theory of degeneration. 

The theory of the continuity of an individual through all the scions, for 
which the stock, or the parent plant rather, serves only as nurse, is based on 
the presupposition that this individual retains all its characteristics un- 
changed during its whole existence as a variety wherever grown and on the 
different stocks. For, at the moment when it must be granted that the habi- 
tat or stock may change any peculiarities, a variation in the length of life 
due to different nutrition must also be considered a possibility. For this 
reason those who defend the theory of degeneration and a fixed life period 
of varieties (especially Jensen among botanists) insist upon the fixity of 
characters and support their theory by the fact that the varietal character 
always remains constant in seeds and in cuttings as well as in grafts. Defi- 
nite shoot variations produced on any one specimen (variegated leaves, split 
leaves, forms with weeping branches, fasciations etc.) which can always be 
transmitted by grafting on new stock are proofs most often stated. 



1 "Wearing out of varieties," Gardeners Chronicle 1875. "Do the varie- 
ties wear out?" ibid. "Degeneration from senility" in the Fruit Manual 1875. 
"Golden Pippin degenerated" in Gardeners' Chronicle 1875. Compare "Bericht iiber 
die Verhandl. d. Sektion fiir Weinbau in Trier," 1875, etc., etc. 



36 

Such statements are refuted by the increasing resuUs of grafting which 
show the mutual influence and change in individuals, incited by grafting. It 
IS known that a form of albinoism, i. e. the condition of having white leaves, 
which we can perhaps call "marbled," is transmissible from scion to stock. 
Differences in the development of a scion dependant upon its being grafted 
on dwarf species or wild stock are known. Just as abundant are the 
examples of changes in size, structure, coloration and taste of the fruit ac- 
cording to the habitat and climate. Finally it should not be forgotten, that, 
in extensive cultivation of varieties, we always find some which "do not 
hold," that is, which from the time of germination show so weak a growth 
that they soon disappear. This indicates a dying out of very young varieties. 
In this instance the theory of senility does not hold. 

In connection with the statement that varieties of fruit formerly highly 
prized no longer thrive and simultaneously run out wherever grown, it is 
interesting to compare some reports dating from the time when the question 
of degeneration became one of paramount importance, which concern directly 
some of the varieties of fruit said to be running out. Hogg stated in 1875. 
in "the Fruit Manual," that Knight had complained of the "English Golden 
Pippin" as a variety at that time degenerating because of senility. He says 
that Mortimer, almost a hundred years before Knight, had spoken similarly 
cf the "Kentish Pippin." Healthy specimens of both varieties, however, are 
still found in England. The length of life and strength of cultivated varie- 
ties (says Hogg) may be proved by the "Winter-Pearmain," which may be 
taken as the oldest English, variety of apple, since it was mentioned in manu- 
scripts as early as about t2oo. The Borsdorfer apple and the well-known 
plum "Reine Claude," are very old. According to Bolle\ the "Reine 
Claude" must have originated in the 15th Century since it was named in 
honor of Claude, the consort of Louis the XII (T490). 

These few examples show that the theory of degeneration due to sen- 
ility of individual cultivated Aarieties or due to other causes has been formu- 
lated because a persistent retrogression has been observed in production and 
healthfulness from time to time iti many localities, from which observations 
general conclusions have been drawn. The fact that in many regions culti- 
vated, well-preserved forms no longer show a thrifty growth and may be 
replaced by others, is undeniable. But this fact only proves that, since each 
culti\ated form makes definite demands in soil and climate, these demands 
can not be satisfied further in many places. Degeneration may be spoken of 
when a cultivated variety runs out universally, even in places where suitable 
conditions have been retained. However, proof of this is lacking. 

The breaking down of the varieties after long cultivation may be due 
to twofold causes, either the cultural conditions have been changed or the 
character of the variety has become different. In the first place, the fact that 
cultural conditions in any one locality are different every year is one to 



1 Quoted in Oberdieck, Pomolog. Monatshefte 1875, p. 240, Bouche and Bolle, 
Monatsschrift d. Ver. z. Beford d. Gartenb. 1875, p. 484. 



37 

which we usually pay too little attention. Aside from the fact that the 
weather of one year always varies from that of the preceding year, the soil 
too is always different ; indeed partly because the time and method of 
working as well as the fertilization and previous cropping in themselves 
ahvays eft'ect changes, and partly because this changed arable land is also 
subjected to changed weather conditions, so that it differs every year physi- 
cally and chemically for the same variety. In the main portion of the book 
a sufficient number of examples of the influence of planting, previous 
cropping, mechanical soil constitution and such factors will be cited and it 
will be shown how these can influence the character and power of resistance ; 
as, for example, to frost. 

In the second place wq think that the running out of a cultivated variety 
can also arise because the variety itself changes its character. According to 
our hypothesis, there is, in all organisms, no stability ; there is no strict ma- 
terial or formal repetition of any process, because the organism changes in 
the smallest unit of time, at each moment confronts the same factors of 
growth as a different organism and strides forward to adjustment. Thus 
each variety, like every term of relationship or of classification, is only a 
frame work made up of common characteristics in which individuals con- 
stantly fluctuate because of lesser variations. 

An excess of nitrogen develops a plant substance different from that 
produced by moderate nitrogen nutrition, a deficiency of potassium makes 
an organ different from that grown with an abundance of potassium. Abun- 
dance of light and deficiency of light develop the cell wall in dift'erent ways, 
great warmth produces more sugar than scanty amounts of heat, etc. Exact 
examples are given in the chapters on the action of individual factors of 
growth. Therefore the organism is like wax which, because of the thrusts 
of the individual z'rgetatiz'e factors, is constantly pressed into other material 
forms. 

The material constitution of the plant body, however, is changed by the 
\ariations of the molecular arrangement which we call chemical changes, as 
well as by the mechanical ones in which the chemical composition remains 
constant. The mechanical disposition of water in the tissues, the substances 
carried in in the water, the tension conditions in the cell wall and the cell 
contents, are all factors which change constantly and as constantly influence 
each other differently. The slightest increase in the supply of light is a 
thrust which not only influences the assimi'atory process, but must also in- 
directly exercise an effect on all other functions. This does not depend at 
all upon wdiether we can define these effects ; — the proof that they must take 
place is enough. 

Let us now consider how the thrusts of individual factors of growth act 
normally on the plant body. Here we notice a peculiar alternation. xAt day- 
break the action of light begins ; — assimilation, evaporation, thickening of the 
cell wall etc. are increased, the whole structure reflects all the phenomena of 
the light reactions. At nisfhtfall. when the after effects of the lieht have 



38 

ceased, processes of oxidation come to the front, phenomena of increased 
turgidity, conversion of starch and the like. The same changes may be ob- 
served in the media surrounding the plant, in the air and soil. A decrease 
of warmth and increase of water content must act powerfully on the plant 
body. With the change between day and night is associated the influence of 
the seasons, which forces upon the plants a period of rest after a time of 
production. Therefore we find in nature a "corrective periodicity." Amid 
these regularly alternating fluctuations of the vegetative factors, the plant 
balances its growth and completes its normal course of development. 

Since the duration and action of these periods in each year differ, the 
production of each plant differs also and the individual years are thus char- 
acterized. We speak of dry and wet years and know from experience that 
in the former, the yield of grain is noticeably large, while the straw yield is 
less on account of the shortness of the stalks. In wet years this is reversed. 
And although the farmer then complains that the baking quality of the flour 
has suffered, yet he emphasizes the fact that he finds compensation in the 
greater straw harvest. 

This example, taken from general practice, shows how great single vari- 
ations in the average periodicity at once becomes noticeable since the prefer- 
ence is shown for different peculiarities of the plant body. As long as this 
kind of one-sideness in development does not threaten the existence of the 
individual plant we may leave the results out of consideration and seek to 
equalize possible cultural variations (as, for example, by the crossing of 
grains possessing poorer baking qualities with those rich in gluten which 
come from dry, warm regions). 

However, the single prevalence of a definite atmospheric factor can also 
lead to direct disease since the effects are cimiulativc. Such an accumulation 
of effects may be compared to the increase in celerity in falling bodies where 
the distance of the fall equals the square of the time. If, instead of gravity, 
we assume another factor, such as v/et, cloudy weather, it will in one day in- 
crease the water content of the tissue while the wall thickening remains be- 
low normal. On the second day, the first day's action is doubled and the 
already porous tissue becomes still more porous. The thrust against the 
plant body, which in itself would not produce disease, is cumulative to an 
extent ultimately threatening the plant's existence. Practically v/e find this 
even within one vegetative period, as, for example, lodging of the grain in 
rainy seasons. The moisture has lengthened considerably the cells at the 
base of the stalk while the deficiency of light has essentially arrested the 
thickening of their walls. The result is that the weakened base is not able 
to sufficiently resist the strain of the wind and gives way. The development 
of the grain is weakened or inhibited, according to the extent of this lodging 
and the phenomena resulting from it, so that the stalk iself is also brought 
to a premature death. 

Corresponding to the above mechanical changes in the wall, the cell 
contents are subjected to changes leading to a diseased condition in the case 



39 

of other influences on the part of the vegetative factor which accumulate 
along one line. We find in heavily fertilized nurseries, whole plots of lux- 
uuriantly growing sweet cherries with open or hidden gum spots and in 
forests whole tracts and healthy looking beds of conifers which show in their 
wood-tissue the beginnings of a resinous condition. In garden cultures 
especially, which on an average are worked with the largest quantities of 
nitrogen, whole plantations suddenly become diseased and are abandoned 
because the "plants will not grow." Enough cases of this kind have reached 
me, in which individual breeders have announced that Begonias, Primula 
sinensis fl. pi., carnations, lilies-of-the valley, cyclamen and others which at 
other times under the same cultural methods had always been produced in 
the greatest perfection, retrogress from year to year and "degenerate." Sim- 
ilar conditions may be observed in field cultures. Entire fields of potato 
varieties which formerly gave faultless crops now easily become black 
specked. Sugar beets grown in the soil best suited to them tend to root rot. 
It has been observed in the root rot of beets that plants grown from trans- 
plants became diseased especially easily, while seedlings from the best and 
heaviest sugar beets showed almost no root rot. Cucumbers forced under 
glass, and those grown in fields in wet, cold years are spoiled by gummosis, 
and the like. 

My experience in remedying such occurrences leads to the conclusion 
that an increase of one definite line of development is concerned in 
these cases which is usually called forth by excess of nitrogen and water. 
Our constantly increasing intensive cultivation not infrec[uently leads to a 
showy luxuriance of the plants and then to a sudden collapse, if the equaliz- 
ing factor is not able to act in a corresponding amount. Accordingly in 
cases of a shown great nitrogen supply, I found the use of calcium phosphate 
to be very advantageous. 

Such one-sided lines of development will also appear necessarily in the 
development of the seed. If it is cultivated from generation to generation 
under the same nutritive conditions, as when first produced, definite peculiari- 
ties of its place of growth must become hereditary through habit. Accord- 
ing to our theory that all peculiarities of an organism represent dynamic 
conditions and molecular vibration-groupings, the habit would necessarily 
be explained as inerfia. The law of inertia of all matter requires that it re- 
mains exactly in the same course and at the same rate of motion. Thus the 
organism keeps on vibrating as it has once been impelled, until some factor 
of vegetation changes the rate of its growth or the direction. 

Practice utilizes this circumstance in the "change of seed," that is, in the 
use of seed from other places which have developed a definite desirable 
peculiarity. Thus the use of Swedjsh grain by Middle-European agricul- 
turalists has become more extensive because it is desirable to take advantage 
of the shorter vegetative period of the northern varieties. While an 
especially developed mealy condition is typical of English wheat, regions 
with opposite climate conditions produce chiefly hard wheat etc. 



40 

Just as useful types of grain arise as the products of atmospheric and 
soil conditions, weakened conditions of the cultivated plants may also be 
produced locally and transmitted through seeds. If these weakened con- 
ditions are repeated from generation to generation by the persistence of 
causes and accumulate, they may lead in the end to a complete decline and 
to premature death. 

Yet this is, however, no degeneration of the species or variety, for all 
these characteristics may l^e reproduced under other cultural conditions. We 
perceive this from the fact that the useful special characteristics introduced 
by a change of seed, are retained only a few years. Then the imported culti- 
Aated forms become changed and assume characteristics such as are due to 
the climatic and soil conditions in the place where they are cultivated. Such 
is also the experience in practice work which constantly attempts in some 
way to accustom (acclimate) highly productive species of a different climate, 
to some one cultural region. 

If it seems desirable to apply the term "degeneration" to the above cases 
of the accumulation of peculiarities leading to a weakening of production 
and to premature death, it is possible at most only to speak of local transi- 
tory degeneration of a number of individuals. It is, however, really only 
a depression of the direction of development, which can be raised again by 
external factors, such as cultural methods. A persistent depression in 
growth as a result of the senility of an originally long-lived variety, is not to 
be assumed within any definite epoch. The disappearance of cultural varie- 
ties is explained by a decreased profitableness resulting from a deficient 
power of adjustment to our agricultural methods, which are constantly be- 
coming more intensive. 



SECTION 2. 



HISTORICAL SURVEY. 

In any branch of knowledge so young as phytopathology, any history 
of the science can scarcely be presupposed. And in fact the date after which 
the teaching of plant disease was set up as a special branch is so recent that we 
are still able to survey completely the course of its development. 

If, however, the form of investigation is still new, the material, viz., 
leports on plant diseases, is very old, extending far back in history. We can 
not go astray in assuming that there have been diseases since the existence of 
the plants began and that observations on these began with their cultivation. 
For we constantly see what heavy injuries are produced by atmospheric ex- 
tremes, and indeed not only ])y those flisturbances which instantly kill the 
plant, but rather by such as weaken the individual in structure and form, 
and slowly lead it toward a premature death, — i. e. make it sick. The action 
of injurious atmospheric conditions must have existed always and have 
made themselves evident in different forms. 

One of the oldest names which we find for certain forms of sickness, 
is "blight." On this account we will attempt to trace the growth of our 
branch of knowledge by following the observ.ations of the diseases which 
this name connates. 

As the later reports show, at first all those phenomena were character- 
ized as "blight," which appeared to the eye to have the color of burned or 
charred matter, that is, black. Accordingly "blight" comprised on the one 
hand the groups of tree diseases, in which the dead bark assumed a black- 
ened appearance, on the other hand also the injuries to grain, the causes of 
which we trace back to smut and rust fungi. 

If we look first in the Bible for mention of diseases and especially of 
"blight," we find, for example, the following: — ^"If there be in the 
land famine; if there be pestilence, blasting, mildezv, locust, or if there be 
caterpillar ; if their enemy besiege them in the land . . . ." Again : — 
'-"The Lord shall smite thee with consumption and with a fever, and 



1 First Book of Kings, Chapter VIII, 37. Second Bool\ of Chronicles, Chapter 
VI, 28. 

2 Deuteronomy, Chapter XXVIII, 22 



42 

with an inflammation, and with an extreme burning, and with the sword 
and with blasting and with mildezv; and they shall pursue thee until thou 
perish." 

From these verses Eriksson^ concludes that these statements, which 
are more than two thousand years old, refer to smut and rust in grain. 
He cites the word Schiddafon (heat) for mildew or blight and Jerakon 
(yellowness) for rust. The following sentences already quoted by Pammel" 
point to mildew in grain : — "I have smitten you with blasting and 
mildew : when your garden and your vineyards and your fig trees and your 

olive trees increased, the palmer-worm devoured them "^ 

Descriptive of the extent of the failure in the harvest is the verse in 
Haggai* : "Since these days were when one came to an heap of 
twenty measures, there were but ten : — when one came to the pressf at for 
to draw out fifty vessels out of the press, there were but twenty, I smote 
you with blasting and with mildew and with hail in all the labors of your 
hands . . . ." 

Among the Greeks, Aristotle (384-322 B. C.) mentions the years of 
rust and Theophrastus of Eresus (371-286 B. C.) recognized the varying 
susceptibility of the different varieties of grain to rust'\ He reports 
also a second kind of phenomena termed blight, i. e. the bark blight of trees, 
since he says (Book 14, Chapter 14) that the cultivated tree? are subject to 
several diseases. Among these, some are common to all trees while others 
attack only certain tree species. One universal disease is the attack by 
worms or by blight. 

Theophrastus, whose statements, according to Kirchner*', are certainly 
based on his own observations, speaks especially of the blight and 
canker of fig trees and mentions in this connection that diseases of trees (as 
of animals) seem to be determined by climate, since in some regions these 
same trees are healthy. The fig tree, he says further, is attacked mostly by 
blight and canker. Blight (Sphakelismos), however, is spoken of when the 
roots become black, canker (Krados) when the branches become so. Tlic 
zvild fig tree, on the contrary, has neither canker nor blight. 

The statement, that some fatalities are due to the influence of atmos- 
phere and habitat, indicates to us the cause of the disease. Such phenomena 
can not really be termed disease, as, for example, freezing and what some 
call blight. In some places certain winds also kill and burn the plants, as at 
Chalcis in Euboea, where the northwest wind is cold, if it blows shortly be- 
fore the solstice. It blasts the trees and dries them, almost more than the sun. 



1 Eriksson, Die Getreideroste. Stockholm 1894, p. 8. (Here detailed historical 
reports on rust). 

2 Pammel, L. H., Weems, J. B. and Lamson-Scribner, The Grasses of Iowa. 
Des Moines, Iowa, 1901. 

3 Amos, Chapter IV, 9. 

4 Haggai, Chapter II, 16-17. 

5 Naturgeschichte der Gewachse. Translated and explained by Sprengel. Al- 
tona 1822. I. 

6 Kirchner, Die botanischen Schriften des Theophrast von Eresos. Sond. 
Jahrb. f. klassische Philologie. Leipzig, 1874. 



43 

It is doubtful whether the disease mentioned here as canker bears any 
resemblance to the outgrowths at present called canker. It is certain, how- 
ever, that woody excrescences were also observed. If actual canker swell- 
ings are not concerned here, yet the phenomena may well have been 
meant, which we would now call knarls. Theophrastus found this kind of 
swellings in olive trees and called them nails or scurf (loxaslopas) because 
they represent bowl-shaped nails on the trees. Sprengel says of these nails, 
that they have occurred recently very abundantly on the olive trees in Italy. 
They appear as round, warty outgrowths of the bark, depressed in the centre 
like a bowl. Among them may also be found similar swellings of the wood 
body. 

It is scarcely credible that the points of view expressed by closely ob- 
servant scholars of Aristotle, concerning the phenomena of disease here men- 
tioned, changed essentially in the course of the following centuries, for other- 
wise the celebrated encyclopaedist Plinius Secundus', who lived from 
23 to 79 A. D. and who possessed a wide knowledge of literary sources, 
would have brought forward further material at the time he recorded scien- 
tifically the statements of Cato (de re rustica) and others as to the influence 
of the stars and the death of trees resulting from cold, heat, unfavorable 
position, soil, fertilization, incorrect pruning and the like. The discoveries 
set down in his "Natural History" contain much worthy of notice regarding 
the influence of atmospheric factors, cultural mistakes, circumstances pre- 
disposing to disease etc. 

In the edition of the "Romischen Prosaiker" by Osiander and Schwab, 
the translator of Pliny (Kiilb) has given a summary of Pliny's sources and 
special remarks on the authors instanced in his "Natural History." There 
is rich material here for a complete history of phytopathology. We must 
content ourselves with a reference to these carefully collected Greek and 
Roman sources and perhaps show by only a fev; more quotations what exten- 
sive discoveries had been made at the beginning of our era. According to this, 
there may be found in the seventeenth book of Pliny's "Natural History," 
Part XXXVII., his statement of the action of frost. He says, "Not the weak- 
est trees are endangered by frost, but the largest ones, and, therefore, when 
they do suffer, the highest tips become blasted, because the sap arrested by 
the cold can not reach that point." We find the following note about the 
phenomena, which we would now call "frost blight," — "The evil influence of 
the stars depends entirely on the Heavens; on this account there must also be 
included among these effects, hail as well as blight and the injury 
caused by white frost. The blight especially attacks tender plants if, enticed 
by the warmth of spring, they venture to break through the ground and it 
singes the juicy buds of germinating plants. In blossoms this is called 
blasting." 

In regard to carefully cultivated grape vines, one reads — "Another bad 
influence of the stars (atmospheric factors) is the covering with dew 



1 Plinii Secundi naturalis Historiae libri XXXVII edit. Janus. Book 17, Chap. 37. 



44 

(roration, the falling on them of cold dew. Kiilb) while they are in 
bloom, or when the berries become hard grains and spoil before they mature. 
They also become diseased, if they freeze and the blight injures the buds 
after pruning. Untimely heat has the same results, for everything has its 
definite measure and goal." At present we summarize the experiences more 
exactly in our teaching of an optimum and of minimum and maximum limits 
for the factors of growth. 

In reference to defective cultural methods it is stated that diseases arise 
when the vine-dresser ties the vines too tightly or injures the roots when 
digging around them and ])arks or bruises the trunk. Under all these con- 
ditions they (the vines) endure wet and cold much less easily because each 
injury penetrates into the wound from without. Scarifying is recommended 
as a remedy because the thickening bark fastens the stems together and plugs 
them. As a protection against the frosts of winter, is mentioned the method 
by which water-ditches are dug about the grape vines in winter, when the 
ground is covered with snow, so that the cold can not blight them. 

The most abundant information as to cultural methods and the evils 
attendant on them may be found in the collection of excerpts from old agri- 
cultural authors, which was made in the tenth century, the "Geoponika." 
We base our discoveries here on the books of the four well-known Roman 
Geoponicists, Marcus Cato, Terentius Varro, Palladius and Junius Modera- 
tus Columella, in which special attention is paid to the practice of fertilization 
and grafting. A compilation of the books on agriculture by the authors 
here named appeared in Cologne in I530\ 

From this work I will choose those places which show that the term 
"rust" as a cause of disease is of very early origin. Thus Varro mentions 
in the first chapter, among the gods, "qui maxime agricolarum duces sunt" 
. . . . "Quarto Robigum, et Floram, quibus propitiis, neque rubigo fru- 
menta, atque arbores, corrumpit, neque non tempestive florent. Itaque 
publicae Robigo feriae, robigalia. Florae ludi. floralia instituti." The ex- 
pression "rust" was used probably for all rust colored, diseased discolor- 
ations in plants, for we find the word Robigo used by Columella to designate 
a disease of grapes which can be avoided, when frost threatens, by smudging 
the vineyards. In his book, "de arboribus," Chapter XIII treats of: Ne 
rubigo vineam vexet. It is recommended "Palearum aceruos inter ordines 
uerno tempore positos habeto in uinea : cum f rigus contra temporis con- 
.'^uetudinem ne intellexeris, omneis aceruos incendito, ita fumus nebulam 
et rubiginem remouebit." The following place is found in the "Enarratio 
priscarum vocum" in regard to the interchangeable usage of "Robigo" and 
"Rubigo" ; "Robigo, deus, quem putabant rubiginem auertere, est aute Rubigo 
morbus segetum"-. 



1 De re rustica M. Catonis liber I., M. Terentii Varronis lib. III., Palladii lib. 
XIV. et I. M. Columellae lib. XIII. Pri-scarum vocum in libris de re rustica enar- 
rationes, per Georgium Alexandrinum. Coloniae, Joannes Gymnicus. Anno 
MDXXXVI. 

- Here, as in the following' citations, we will follow our sources exactly. 



45 

The next fifteen hundred years accepted the observations and theories 
of the Romans, which may be found collected in Pliny. For E. Meyer^ 
leports from Petrus de Crescentiis who wrote his great work in 1305, 
the first eight books of which treat of agriculture, that since Palladius 
no one had' written anything in Latin on agriculture. Only fragments of 
the Greek collection of the Geoponika were to l)e found. The older works 
of Varro and Columella we';e no longer suited to existing conditions, so that 
there was need of an up-to-date book on agriculture. Yet the book by Petrus 
de Crescentiis actually contained less than the books of the older authors, al- 
though he strived for a sciei:tific foundation for agriculture and gave num- 
erous directions for grafting various kinds of trees, in accordance with the 
favorite pursuits of antiquity and of th.e middle ages. In the same way in 
1600 Colerus" also only repeated the earlier statements regarding the 
cutpushings of the bark, — "Inflammation of trees" ("Schwulst der Bewne") 
under which there develops a putrid Ii([uid. In this book the iniluence of the 
stars was believed in, with unshaken firmness. For example, in his "Horti- 
cultura" published in 1631, the renov/ned Professor Peter Lauremberg'' of 
Rostock relates that certain stars like Orion, the Pleiades and others exert 
an especially injurious infiuence and that, as a result of injurious atmos- 
pheric influences, the so-called "secret evils" arise, among whicli belong rust, 
carbuncle and mildew. 

We can naturally expect to find progress in the recognition of the sig- 
nificance of disease among practical workers, whose cultural efiforts are most 
sensitively disturbed by injuries making themselves felt in their work. The 
book of the "Electoral Superintendent of Gardens," — Heinrich Flesze^, — 
which was famous in its time, is interesting in this connection. He 
speaks of the blasting of the branches which he calls "blight and cold," 
"otherwise there are three chief causes for the blighting of trees. First, 
superfluous moisture which, with inflammation of the sap, is collected be- 
tween wood and bark, distending the latter and blighting and blasting it. The 
second is this, — that of times, thoughtlessly and v/ith a lack of judgment, the 
tree is set in a postion dift"erent from the one in which it stood before. This is 
very injurious, since the bark where it is brownish and has been exposed to 
the east or south, is therefore much harder than on the sides toward the 
north or west. These are generally green, tender and immature. Therefore, 
some injury must inevitably arise from this, since the north side is not at 
all accustomed to the southern sun and is not only blasted by the great heat 
but in the spring is injured by the hard frosts ; the bark is raised, then later 
in the day dried up and scorched by the sun. From this the blight at once 
arises, since it is commonly noticed on th.e southern side." Flere we have posi- 
tive personal observations. The author relates further that he has never- 



1 Geschichte der Botanik. Vol. IV, p. 148. 

- M. Joannis Coleri, Oeoonomia und Haussbuch etc. Ander Theil. Wittenberg 
1600. Book V. Chapter 12. 

3 Petri Lauremberg-ii, Rostochiensis Horticultura. Francofurti 1631. Cap. XXXV. 

4 Heinrich Heszens, Neue Gartenlust etc., enlarged and provided with three 
useful indices by Theodorum Phytologum. 1690. Chapter VIII. 



46 

theless preserved trees thus reversed in position by placing a covering of 
cow manure, oat chaff, glue and ashes on the side of the tree unwisely turned 
toward the south. "The third case, however, arises when a bread knife is 
used in grafting etc." Perhaps Hesze has in mind here some parasitic in- 
fection and attempts to explain it. 

Hesze (p. 312) writes "that canker ("Krebs") really orginates from the 
grafting of a tree at the time when the moon lies in the sign of the crab or 
scorpion . . . ." "This disease may be recognized by the fact that here and 
there the bark throws up little hummocks under which the tissue is dead and 
black. This spreads further and further, ultimately infecting the whole trunk. 
Many scattered causes of canker have been brought forward, but the one 
given above is the most probable of all." The Editor makes the following 
addition to this statement, — "So far as canker is concerned, no one 
can deny that it often arises high up on the trees, and, in fact, in the accumu- 
lations of dirt which collect between the trunk and the branches at their 
crotches. On this account, it is most necessary that the crotches always be 
kept clean and freed from all dirt. Thus the canker often arises from the 
same rising sap which produces blight and the two diseases often have but 
cne cause." 

The author clearly describes the phenomenon which we now term limb 
canker and, instead of "ascending sap," we insert, injuries due to frost with a 
subsequent infection by Nectria ditissima; his presentation corresponds with 
our present conception of blight and canker. 

About this time in France, de la Quintinye wrote "Le parfait jardinier"^ 
which is still much sought after. In this we find canker briefly 
mentioned as a kind of gall (signifie une maniere de galle ou de pourriture 
seiche), formed in the bark and the wood and often found on pears (Poire 
de Robine, Petit Muscat, Bergamotte), on trunks as well as branches. The 
conception of the swellings of the wood indicated by the term "canker" Is 
found further in the writings of later horticultural authors, as, for example, 
in Fischer-. 

The boastful Agricola^ (born 1672) stands independent, that is, 
on his personal, repeated and practical experience. His actual service is 
found in his numerous experiments, carried out from 1712-1715, on the vege- 
tative reproduction of plants (especially by roots). He devotes the fifth 
chapter to "occurrences and diseases" and expresses himself, for example, 
as follows : — "Mildew, Rubigo, however, prevails at times, as a pestilence 
among trees. In spring, when the earth opens and the enclosed vapors be- 



1 Le parfait jardinier etc. Par feu Mr. de la Quintinye. Paris 1695. Vol. I., 
p. 31. 

2 R. P. Christophori Fischeri soc. j, Fleissiges Herrenauge etc. Niirnberg 1719. 5 
Section I., p. 168. 

3 Georg- Andrea Agricola, Philosophiae et Medicinae Doctoris und Physici 
Ordinarii in Regensburg, Versuch einer allgemeinen Verhmehrung aller Baume, 
Stauden and Blumengewachse anjetzo auf ein neues iibersehen usw. von C. G. 
Brausern. Regensburg 1772. The original title read, — "A new and unheard of ex- 
periment, well founded in nature and in reason, for the universal increase of all 
trees, bushes and flowering plants," 1716. 



47 

gin to rise, it injures most of them and is nothing else than a very sharp and 
biting dew, originating in the earthy vapors and conducted from them .... 
In the third place a disease occurs among trees, which is called sunblight, or 
blight, livedo, which, however,_may be of two kinds. First, when a fine rain 
or dew falls or settles on the leaves while the sun shines, the ducts or tubes, 
becoming flabby and distended, are contracted at once by the heat of the sun. 
Thus the leaves are scorched, begin to turn brown and black and fall. In 
the second case, the urcdo or blight is found in the inner parts of the trees, 
in the pith .... The true cause, however, for the blighted pith, when 
the tree is transplanted, may well be, that the common gardeners have the 
habit, in transplanting, of pruning all the roots and do not understand how 
much they are injuring the tree. For the smallest roots draw the most sap 
from the earth, and these are the ones they cut ofi .... Now because 
the root, together with the pith, is open and exposed, moisture can penetrate 
and injure the pith . . . ." 

In regard to canker, we find the ''ascending sap" emphasized as its 
cause in the horticultural lexicon by Riedel published in 1751'. "Can- 
ker, tree-cancer, canker, devourer," thus is listed the injurious attack 
on the trees which appears in the bark, — since it forms hummocks here and 
there and springs up. — And therefore, if the devouring evil is not overcome 
in time, one branch after another, and eventually the whole tree, is ruined 
. The real cause, however, of this injurious attack on the trees is 
cither the evil peculiarity of the earth and the evil juices produced or arising 
from it which become so inflamed within the bark that this looks black when 
removed, or the ascending superfluous rank juice, which, finding no escape, 
must clog and spoil, thus becoming the cause of the out-pushing and bursting 
of the bark." 

Instead of the ascending sap, the expression — "congestion of the sap," 
is used at present. 

As a remedy for canker, this author recommends cutting out the dis- 
eased places and coating with grafting wax. If the cause lies in the soil, this 
should be removed up to the roots and replaced by new soil. When the sap 
is excessive, the base of the tree trunk should be bored in February, and the 
hole wedged open for i to 2 days Math a firm wooden peg or a strong root 
should be split, " since the superfluous sap will then be drawn downward." 

Philipp Miller- traces phenomena of disease directly back to frost, 
and calls them "bUght." Miller's decisions are essentially a repetition 
of Hale's theories that by blight (blast) not only frost but also sun scorch 
etc. are understood. Hale's^ statements are important because he men- 
tions the transmissability of canker in budding and of its occasional heal- 
ing by being cut out. The observation of this English experimentor on the 



1 Riedel, Kurz abgefafstes Gartenlexicon usw. Nordhausen 1751. p. 420. 

2 The English Garden Book or Philipp Miller's "Gardener's Lexicon" etc. 
From the Fifth Edition translated into the German by Huth. Nlirnberg 1750, p. 136. 

3 Statical Essays containing Vegetable Statics etc. by Steph. Hales. 2nd edition. 
London 1731. I. 35ff., 147, 369; II, 265. 



48 

influence of the dry spring winds, which scorch the foHage is worth noting: — 
"The considerable quantity of moisture which is given off from the branches 
of trees during the cold winter season, plainly shows the reason, why, in a 
long series of cold, northeasterly winds, the blossoms and tender young set 
fruit and leaves are so frequently blasted in the early spring, viz. by having 
the moisture exhaled faster than it can be supplied from the trees." 

DuhameP pays great attention to injuries from frost and states 
that trees are often attacked by swellings which may be more easily healed in 
} ounger than in older trees. At some place on the trunk, the bark is loosened 
from the wood and a devouring pus occurs between the two. Devouring ab- 
scesses of this kind are called "canker" which is counted among the diseases 
produced by a superfluity of sap. Das Niedersachsische Gartenbuch- finds 
the cause from blight and canker in too thick standing of the trees, in un- 
favorable soil etc. 

While in ancient times and in the middle ages observations on plant dis- 
eases were usually limited to a perception of the mature phenomena visible 
to the naked ^ye and the solution of the questions of plant life were sought 
almost entirely among experiments of budding, we find that the experiment 
itself attained its own importance with Hales and Duhamel. 



Simultaneously with experimental physiology came the wider classifi- 
cation of plant diseases. 

We follow here Seetzen's'' treatment of the subject and its history. 
Seetzen states that Tournefort had a finished system*. His first class 
mcludes the diseases due to internal causes, as opposed to the sec- 
ond class, the diseases produced by external causes. To the first class he as- 
cribes : — I -La trop grande abondance du sue nourricier; 2-le defaut ou 
manque de ce sue; 3-quelques mauvaises qualites qu'il pent accjuerir; 4-la 
distribution inegale dans les differentes parties des plantes. In the second 
class belong: — i-La grele ; 2-la gelee ; 3-la moisissure : 4-les plantes, qui 
naissent sur d'autres plantes : 5-la piqueure des insectes ; 6-differentes tallies 
ou incisions, que Ton fait aux plantes. 

We find Tournefort's point of view in our modern systems. We group 
the diseases caused by excess or deficiency of water and food, with injuries 
produced by weather extremes (frost, hail) etc. In the same way, we treat 
wounds as a separate division. The parasitic diseases appear for the first 
time as such in Tournefort's book. 

Less fortunate is Zwinger's"^^ system which appeared shortly after 
Tournefort's and which also is formed of two main groups, — (r) General 



1 La physique des arbres par Duhamel du Monceau. Paris 1758. p. 339. 

- Caspar Bechstedt, Vollstandiges niedersachsiches Land- und Gartenbuch. 
Flensburg- und Leipzig- 1772. I, p. 151. 

a Systematum generaliorum de morbis plantarum brevis diiudicatio. Publico 
examini submittit Ulricus .Jasper Seetzen. Gottingae MDCCLXXXIX. 

4 Observations sur les maladies des plantes par M. Tournefort. Mem. de I'Ac. 
Roy. des Sciences a Paris 1705, p. 332. 

5 Jo. Jac. Zwingeri, Diss. med. inauguralis de valetudine plantarum fecunda et 
adversa. Basileae 1708. 



49 

and (2) Specific diseases. The first includes : — La gangrene — le desseche- 
ment — la surabondance de sue — le branchage excessif — une espece de galle, 
qui manche I'ecorce. In the second main group we find : — Le dessechement 
des racines — la separation de leur ecorce — la grosseur excessive des racines, 
qui retienent tout le sue de la plante — les excroissances — les coups et les 
biessures. It is evident from this division of closely related phenomena that 
the author had not fully mastered his material. 

Eysfarth's^ system gives a classification which the layman easily 
grasps. It uses as its basis the difl'erent periods of the plant's life. In 
the first class are the diseases of the period of germination ; in the second, 
those of the actual vegetative period and in the third class, the disturbances 
of the sexual period. LTnder each class are discussed the influences of 
weather extremes, injuries due to animals and other wounds. In this book 
there is also a chapter "a rubigine aut pruina." The thoroughness of the 
classification shows that the author had well worked out his material. 

Adanson^ returns to Tourne fort's division since he sets up as his 
first main group the "maladies dues a des causes externes," and as the 
second, the "maladies dues a des causes internes." Even the introduction 
shows the advance in microscopic investigation and the increased attention 
paid to parasitic fungi ; under the first main group, the difl^erent chapters 
take up, for example, Le givre ou Jivre (Erysiphe Fabricii) — la rouille 
efiu^tifyj Theophr. (Rubigo) — le charbon (Ustilago) — la pourriture (Caries 
Fabr.) etc. 

Adanson often uses the terminology of Fabricius who probably had 
published his studies in separate treatises before his classification had ap- 
peared as a whole, for his complete classification did not appear until 1774^. 

Fabricius certainly based his views on his own observations. This is 
less noticeable in the formation of the main groups than in the sub-divisions 
of the difl^erent chapters, in which a classification of the cases according to 
their different causes has been stated, even when the external appear- 
ance was similar. Thus, for example, we find in the first main group : — 
"Vfrugtbargiorende Sygdomme," i. e. the disturbances leading to sterility ; 
a section "Dovhed" which may be translated by etiolation or the yellows. 
This is divided into D. af Regn, af Kulde, af Rog etc. His observation that, 
besides rain, cold and other factors, "yellows" may be produced by smoke 
is also worth notice. In the second main group, "Udtaerende Sygd," i.e. the at- 
rophias, there is found under the section "Quaelelse," etiolation from "stedets 
Indslutning" (too close planting), from "paa Lys" (lack of Hght) and from 
clinging plants and insect injuries. Another group is separated from these 
phenomena, — -""Taering" (Tabes, Jaunisse in Adanson) where the yellowing 
is due to insufiicient nutritive substances, unsuitable soil conditions, ex- 



1 Christ. Sigismund Eysfarth, Diss, piiys. de morbis plantarum. Lipsiae 1723. 4°. 

- Adanson, Sur les maladies des plantes; in "Families des Plantes." Vol. I, p. 42. 
1763. 8°. 

3 Fors6g- til en Af handling om Planternes Sygdomme ved Joh. Christ. Fabricius; 
ind der kongelige Norske Videnskabers Selskab skrifter femte Deel. Kjobenh. 1774. 
Sid. 431-492. 



50 

cessive evaporation after transplanting etc. The third main group is taken 
up with "Flydende Sygdomme," that is, sap-currents, under which is included 
honey-dew. In the fourth group are found the "Raadnende Sygdomme" 
which, according to our point of view, might be termed soft rot, putrefying 
bacteriosis or scrofula. Among the causes figure also the "Snylte-Planterne," 
i. e. parasitic plants. In the fifth and sixth groups, wounds, frost splits, galls 
and monstrosities are treated. 

In 1779 appeared the German translation of the Zallinger^ classi- 
fication with the evident endeavor to utilize the terminology of animal path- 
ology in plant pathology. Zallinger makes five classes: — (i) Phlegmasiae 
or inflammatory diseases; (2) Paralyses seu debilitates, laming gouts or de- 
bility; (3) discharges and draining; (4) Cachexiae, bad constitution of the 
body; (5) chief defect of the dififerent parts. In order to characterize his 
theory, let us look for the disease which, with blight, forms the main example 
in our entire presentation, — viz. canker. Zallinger puts this in the class of 
the Cachexiae, in the subdivision of the ulcers, under which he includes rachi- 
tis or abortive growth, leontiasis or rough warts on the skin and others. He 
mentions blight, Gangraeno s. Sphacelus as an abnormal Cachexia, together 
with Phthiriasis or lousy disease and Vermiculatio, the production of worms. 
From this classification it may be concluded that the author has let himself 
be guided by the frequently similar appearance of the phenomena, for the 
dead places in the bark offer a favorable centre of attack by insects. What 
we now term grain smut is found as Ustilago, or deformity of the seed, under 
the class of draining. Fabricius had placed "Kraebs," Cancer, in the class 
of diseases of decomposition. 

Batsch-, in his introduction to the knowledge of plants, also pub- 
lished a survey of the diseases which he divided into those based on the ''de- 
composition of the firm and fluid parts," i. e. on the constitution of the plant, 
and into those caused by "animals and plants." 

Any one, however, looking for our cr3^ptogamic parasites in the latter 
section would be deceived. These are rather to be found in the first class, in 
agreement with the conviction already advanced by Zallinger fs. Ustilago), 
that the parasitic organisms are not independent plants but only develop- 
mental forms of the higher plants. Thus Batsch under constitutional dis- 
eases has one group "Brandige Veranderung des Wesens," change of char- 
acter due to blight, the first family of which includes the phenomenon, where 
a decomposition of the tissue into powder "smut, Ustilago" takes place. The 
second family contains the transformation of the tissues into "a spongy mass 
(Ergot, Clavus)." 

These views remained in force for some time, as will be seen from the 
following section. 



1 Abhandlung- iiber die Krankheiten der Pflanzen, ihrer Kenntnis und Heilung-; 
translated from the Latin by Job. Count v. Aauersperg-. Augsburg 1779. 8°. 

2 A. J. G. C. Batsch, Versuch einer Anleitung zur Kenntnis and Geschichte der 
Pflanzen etc. I. Theil. Halle 1787. p. 284. 



51 

By means of the works of the authors mentioned and the discoveries of 
practical horticuUure, as well as the great sensation called forth by the tree 
wax for injured trees which was discovered by William Forsyth in 1791 and 
universally overestimated, the conviction of the agricultural significance of 
plant diseases was extended over so wide a circle that special books could 
now be published for this branch of knowledge. 

The year 1795 makes us acquainted with three such works. The first 
one written by Plenk^ treats of the diseases of all cultivated plants 
of importance at that time and is based on thorough observations. He de- 
scribes thus :— "a spongy large outgrowth at some place on the trunk from 
which exudes, even in the most scorching weather, a caustic moisture which 
corrodes the whole extent of the swelling." Thus Pyrus Cydonia, standing 
near a swamp, was attacked by tree canker while other quince trees planted 
in a higher place were healthy. The sap, it seems, becomes so caustic from 
the acidity of the standing water that it eats up the ducts. There are two 
kinds of tree canker determined by the difiference in the location of the dis- 
ease; first, open tree canker, when the canker knots appear on the external 
surface of the bark ; second, hidden canker, when a sharp cancerous pus 
collects between the bark and the wood but does not escape from the bark 
in any place. In both cases the tree becomes incurably wasted, when the 
parts attacked by canker are not cut out at once and covered with wound 
wax. In this blight Plenk distinguished between a dry and a moist blight. 
By the first he means "a black and dry wilting of the leaves or of some other 
part of the plant" and by "moist blight" he designates the "moist and soft 
degeneration of the plants into a putrid pus." 

We find almost the same terminology in the explanation of canker in 
Schreger's- book which otherwise gives many of his personal obser- 
vations. In regard to the phenomena of blight in which the bark or other 
parts of the tree appear black and soft and are consumed, he says, "Such 
black spots of the bark grow further and further round about themselves 
even attacking the wood so that the bark itself at last splits ofif, as if dead, 
and the wood appears dry and black, as if burned." This explanation cor- 
responds exactly with the phenomena which we perceive when frost causes 
considerable injuries to the bark. In fact this observer arrives at the same 
conclusion as we do in regard to the cause. "Bruises from hailstones give 
rise to its production and also cold frosts. This frost is more injurious in 
low and moist regions than in high dry ones. For this reason there is less 
injury from frost on windy nights than on clear, cold ones. If the trees 
freeze in winter and die, the cause of their death is usually a blight induced 
by this freezing. This happens sometimes when the severe cold comes too 
early in the autumn while the sap is still flowing actively ; sometimes in the 
spring when the sap, so to speak, has begun to run. The latter case is the 



1 Plenk, Physiologie und Pathologie der Pflanzen. Wien 1795. 

2 Erfahrung-smassig-e Anweisung zur richtigen Kenntnis der Krankheiten der 
Wald- und Gartenaume. Leipzig 1795. 



52 

most dangerous of all. Even in midwinter with very great cold they rarely 
freeze ; it might be when it has rained the day before." On pages 420 and 
500, he says of apple and pear trees that "an excess of fatty, oily fertilizers 
easily develops blight and canker," i. e. creates a predisposition'. 

The third one of the books published in 1795, the one by Ritt^r v. Ehren- 
fels^ is even more specialized, for he treats only of fruit trees. He 
declares that all kinds of trees would be subject to blight and that "this decay 
which appears first in the bark and then in the wood" is the most common 
disease of trees and in some books is termed canker. The description which he 
gives is so clear that it can be identified as the phenomenon now known as 
Nectria-canker. He says, "the indication of this evil attack is first of all a 
black or blackish bark which, six or eight days after its appearance, is often 
pushed out, forms little splits and gradually loses its connection with the 
trunk of the tree so that it clings only loosely to the shaft. After some time 
the loose bark is entirely separated from the trunk and exposes the wood. 
In this new stage the vitality of the sick plant does its very best to help itself 
and unceasingly throws oft' the unfavorable or sick parts, but this vitality 
finally becomes weakened and the tree dies. The tree attempts to form a 
new bark which grows in folds more or less overlapping and tries to cover 
the exposed places" .... He ascribed the cause to injuries as. for 
example, from injudicious pruning, injuries due to insects and the like, "even 
at times the tendency to blight lies in the disposition of the tree itself, — a 
disposition which the trees obtain from the soil in which they grow, from 
their descent and from an unwise cultivation." 

In the pomological glossary published at the beginning of the last cen- 
tury, Christ" added to the above by the further statement, that the blight 
"often is due to freezing in winter." 

Burdach^ also bases his statements on his own observations and 
says of blight, "this disease is an indirect result of weakness and commonly 
arises in those trees whose growth has been hastened by strong forcing and 
fertilizing or which have been transplanted to a poor garden soil where only 
the upper part of the ground has been improved. In cherry trees, still an- 
other evil effect arises from the same cause, viz. the exudation of resin or 
gum." 

The theory of the influence of the soil and fertilization, as among the 
most important causes of plant diseases, is now laid aside for some time and 
attention is given to the manifold and extensive investigation of the province 
of fungus life. 



Although antiquity had already recognized a number of edible and 
poisonous fungi, yet their attentive observation and systematic study began 

1 Ritter v. Ehrenfels, Ueber die Krankheiten und Verletzungen der Frucht- 
und Gartenbaume. Bresslau, Hirshberg- und Lissa 1795. 

- Pomologisches theoretisch-praktisches Handworterbuch. Leipzig 1802. 
3 Systematisches Handbuch der Obstbaumkrankheiten. Berlin 1818. 



53 

first in the Middle Ages with the foundation of classification of the vegetable 
kingdom. According to the statements of Corda^, Andreas Caesalpinus 
(1583) was the first to gather together the fungi in his celebrated book "De 
plantis." He describes sixteen genera, Tuber, Peziza, Fungus, Boletus, Suil- 
lus,Prunualus, Prateolus, Familiola, Scoroglia., Fungus marinus, Gallimaceus, 
fungus panis similis: Lingua, Digitellus, Igniarius and Agaricum. As it 
seems, even marine animals have been included here. After almost one hun- 
dred years appeared Joannis Raji's "Methodus plantarum" Londini 1682. In 
1710 Boerhave followed with his "Index plantarum horti Lugdano-Batavi" 
and in 1719 Tournefort appeared with his "Institutiones Rei herbariae." 

The chief work to which modern mycology must refer appeared in 1729 
in Micheli's "Nova plantarum genera" in which the fungi are most carefully 
described and illustrated in more than 100 pages and with 12 plates. Micheli 
studied their life phenomena more closely and was the first to observe the 
attachment and dissemination of spores. Among the genera there described 
are found those which are considered in plant diseases, Aspergillis, Botrytis, 
Puccinia (now Gymnosporangium), Mucor and Lycogala. 

There now follow in cjuick succession "Methodus fungorum" by Gled- 
itsch (1753) and the "P^ungorum agri ariminensis historia"by Battara (1755), 
in which a special chapter treats of the usefulness and injuriousness of fungi. 
The close systematic description of the different genera and species begins 
with Linnaeus' "Systenia Naturae" (1735), the "Methodus sexualis," the 
"Genera plantarum," the "Corollarium generum" and the "Philosophia 
botanica." The third edition of this book, published in 1790 by Willdenow, 
contains an exact list of all botanists up to 1788. The work also mentions 
a number of diseases (Fames, Polysarchia, Cancer, etc.). On page 
245 of the present edition by Willdenow, are found the following remarks 
on parasitic diseases : — "Erysiphe Th. est Mucor alhus, capitulis, fuscis ses- 
silibus, quo folia asperguntur, f requens in Humulo, Lamio. Acere" etc. . . . 
"Rubigo est pulvis ferrugineus, foliis subtus adspersus, frequens in Alche- 
milla, Rubo saxatili . . . ." "Ustilago, cum fructus loco seminum fari- 
nam nigram proferunt. Ustilago Hordei C. B., Ustilago Avenae C. B." . . . 
Then follow notes on Ergot, galls and other malformations, changes in color 
etc. It is of importance to pathology that this exact systematist can not sup- 
press the fact that really no two individuals resemble one another and that 
climate as well as soil constantly act in a modifying way on the organism. It 
is stated in fact in the Philosophia botanica, "Varietates tot sunt quot differ- 
entes plantae ex ejusdem speciei semina sunt productae. Varietas est planta 
mutata a causa accidentali : climate, solo, calore, ventis etc. ; reducitur itaque 
in solo mutata." .... Scopoli's book "Dissertationes ad scientam 
naturalem pertinentes" (1772) treats especially of subterranean plants. In 
1780 the publication of BuUiard's "Herbier de la France" was begun in 
Paris, in which the different genera are illustrated on 6(?o colored plates, 
(among others Mucor, Trichia,Spliaerocarpus,Nidularia. Hypoxylon). After 

1 Anleitung zum Studium der Mykolog-ie. 



54 

Batch's "Elenchus fungorum" had appeared in 1783 in Jena and, between 
1788 to 1791, Bolton's "Historia fungorum, circa HaUfax sponte nascentium," 
in which only Linnean genera are described, there was published in 1790 in 
Ltineburg Tode's valuable work which abounds in personal observations, 
"Fungi mecklenburgenses selecti." The extremely careful illustrations include 
among others, the genera Acrospermum, Stilbum, Ascophora, Tubercularia, 
Helotium, Volutella^ Hysterium, Vermicularia, Pilobolus which we now find 
among the excitors of disease. A. v. Humboldt, in his "Florae fiibergensis 
specimen" (1793) has also described a considerable number of genera. 

But all these works, nevertheless, are to be considered only "contribu- 
tions." A comprehensive methodical classification was first given by Per- 
soon's "Synopsis methodica" (Gottigen 1801), for long a standard. There 
appeared in England, from 1797 to 1809, a work by James Sowerby con- 
taining 439 plates of valuable illustrations with the title "Colored Figures of 
English Fungi or Mushrooms." 

Mycologists now tended more and more toward the study of the mi- 
croscopic fungous forms even if the optical instruments of the time did not 
make possible more exact observations. This applies first of all to Linck's 
"Observationes in Ordines plantarum naturales" published in the "Schriften 
naturforschender Freunde zu Berlin" (3. Jahregang 1809-1810) and the 
illustrated work by Nees v. Esenbeck, abounding in copies from earlier books, 
"System der Pilze und Schwamme," Wiirzburg 1817, which contains a sum- 
mary "of the theories of the lower vegetation stages in hi.storical fragments." 
Here also are the statements of investigators believing in spontaneous gene- 
tation. The author himself, if we understand correctly his grandiloquent 
natural philosophical presentation, considers the parasitic fungi in the lowest 
possible groups as structures produced from the mother plant itself. Thus 
he says, for example, of the Entophytes, "Their most peculiar characteristic 
is that they belong to the overloaded or exhausted life and generally, if not 
always, develop first under the common covering without any mixture ex- 
tending over the whole, and originally only in isolated places, formed in- 
dividually from the life of the whole. The dependence of the mfusorial cell 
on the higher organisms is always shown by its superior position, due to its 
more or less lengthened stem. The cell grows before it has become free and 
its elongation on this foundation is the expression of the condition of polar- 
ity which has been brought about, not suddenly but organically, and which 
passes over into the cell from the main plant." Under the genus Cyathus 
(one of the puff balls) (p. 141) it is said "the whole trunk species which 
we have described is only a thread of dust originating from the earth itself. 
The dust of the puff balls begets itself . . . ." 

At this time Elias Fries' classic work was published including all 
the known varieties of the fungus kingdom with clear diagnoses of 
genera and species. 



1 Systema mycologicum T. I to III. I.undae 1821, Gryphiswaldiae 1829 to 1832- 
Elenchus Fungorum. Gryph. 1828. 



55 

The literature now begins to be increased by single works, scientific as 
well as practical manuals and writings on both agriculture and horticulture 
which treat of diseases (Tessier, Jager, Hopkirk, the text books of Willde- 
now, Nees, de Candolle, Wenderoth, Reichenbach, Re and Kieser) to such 
an extent that we can now emphasize only those publications which deal most 
fully with the history of pathology. 

Among these belong primarily F. Unger's^ "Exantheme der Pflanzen" 
published in 1833 and giving the results of the most industrious 
and conscientious studies. This physician, living in a small isolated Alpine 
valley, supplements his observations by many very careful original drawings, 
true to nature, on which he constructs his theory of disease. "Most plant 
diseases are located in the juices .... The faulty formation and the 
numerous abnormalities in the chemical process of the nutritive juice as well 
as similar faults in the more highly active life-sap, are the causes of innumer- 
able diseases which become evident in a scanty formation of the plant sub- 
stance, the accumulation of excretory substances, the breaking up of the 
parenchyma, the changed constitution of the secretions etc., or by conditions 
of an opposite character. In every case, most of the quantitatively and quali- 
tatively changed processes of the vegetative "chylopoese" might be taken 
as the source of diseases which may be recognized from the change in sub- 
stance rather than from that of form. The position into which a large 
number of the plants are transplanted often acts so detrimentally upon them 
that at least the greater part deserve to be called diseased." 

Although, according to this presentation, we must suppose on the whole 
that Unger would consider diseases as functional and formal variations in 
the life-history of the organism, he, nevertheless, arrives at the conclusion 
that disease is something foreign. "For just as the cosmic and elementary is 
related to the organic, child-like, antitypical, as something parental or typical, 
in the same way the organism is related to the disease zvhich is nothing else 
than a second lozuer organism whose elements already lie hidden in some 
other higher one." In this theory lies the continuation of the thought ex- 
pressed by Batsch on the nature of the parasitic organisms. 

Unger states that "among the plant diseases least betraying any depen- 
dence upon the organism attacked and which in their root formations are 
still so intimately interwoven with this organism, there belong indisputably 
those forms which we designate by etiolation, dropsy (anasarca), jaundice 
(icterus), tympanitis, tabescence(tabes), failure of crops, proflu via and others. 
These form in fact by far the majority. Greater independence is shown by 
the vast army of malformations, at the basis of which always lie deiicicncies 
in the amount of sap and therefore a retardation in lower developmental 
stages. Honey-dew (Sac char ogensis diabetica) is more important than these. 
Its pathological course was first recognized by L. Treviranus and its more 
universal significance by Dr. H. Schmidt. Mildew is indisputably related to 



1 Die Exantheme der Pflanzen und einige mit diesen verwandte Krankheiten 
der Gewachse. Wein 1833. 



56 

this disease : the straining toward a more complex organization of the exuded 
juices is made evident here by organic formations wliich are missing in 
honey-dew. These organic formations are still more independent in rust 
dew (Fuligo vagans). Finally the disease organism appears in the excre- 
tions and the forms nearly related to them as a peculiar, complete entity. 
Parasites belong here— the highest among them, such as some kinds of Lor- 
anthus, seeming to have separated themselves entirely from the mother 
body." 

Unger's views are also shared by Nees v. Esenbeck and A. Henry^ 
who state in regard to puff balls that "the fungi clearly stand here 
at the lowest level . . . ." "They are correctly considered as the ma- 
terial of disease, as secretions of the higher plants." "The leaf fungus is 
formed in general by a coagulation of the juices discharged into the inter- 
cellular passages." 

Theodor Hartig also wrote his work on the red and white rots of the 
pine under the influence of this theory. In this he confirmed first of all the 
co-operation of fungi (Nyctomyces)'. He traced the production of these 
fungi to a decomposition of the cell walls. 

Of the works which take up general constitutional diseases and scarcely 
touch upon the fungi, we will name those by Geiger^ and Lindley* 
which in all essentials are based upon practical experience. On the 
ether hand, however, Wiegmann's^ statements are evidently based 
on microscopic studies and the bearings of chemistry, for example, he 
states that the pus of the blight, as well as that of canker, contains putric and 
huniic acids, but that that of the blight contains more putric acid. To him 
both diseases appear non-parasitic in nature and he thinks canker (Caries, 
Necrosis) always arises from "a stoppage and deterioration of the juices, 
even if these were never present in excess." Among the causes 
mentioned are injuries to the roots, or injuries from frost and unfavorable 
soil conditions, as, for example, "If the subsoil is moist, sour, stony or other- 
wise unfertile, or contains swamp ore." 

Meanwhile, after Corda's*^ great work on fungi had begun to ap- 
pear, Meyen's" "Pflanzenpathologie" was published as a standard, which 
even now warrants consultation. He divides his material into "External 
Diseases" and "Internal Diseases." Among the former, besides the injuries 
due to man and to animals, the formation of gnarls and galls, he includes 
also phanerogamic and cryptogamic parasites, of which the Ustilagineae 
and the Uredineae as well as other fungi are treated in detail, according to 



1 Das System der Pilze, Section I. Bonn 1837. 

2 Abhandlung- liber die Verwandlung- der polycotylen Pflanzenzelle in Pilz und 
Schwammgebilde und die daraus hervorgehende sogenannte Faulniss des Holzes. 
Berlin 1833. 

3 Die Krankheiten und Feinde der Obstbaume. Miinchen 1825. 

4 The Theory of Horticulture. London 1840. 

5 The Krankheiten und krankhaften Mifsbildungen der Gewachse von Dr. A. F. 
Wiegmann sen. Braunschweig 1839. 

6 Icones Fungorum hucusque cognitorum. Prague 1837 to 1854. 

'^ Pflanzenpathologie. Lehre von dem kranl^en Leben und Bilden der Pflanzen. 
Published after the death of the author by Dr. Gottfr. Nees v. Esenbeck, Berlin 1841. 



57 

the standpoint of the time. Meyen no longer shares Unger's view that the 
parasites as excrement-organisms are the product of a formative development 
latent in each plant, the disease occurring in a more or less developed form 
and state of independence according to the constitution and strength of the 
host-organism. On the contrary, his Plant-Pathology, in the discussion of 
smut fungi, emphasizes especially that "observations on the production of 
the smut show most clearly that we have to do here with true entophytes : 
we will find that some smut species are shown as particular parasitic growths 
in the interior of the cells of the plants attacked by them and that the smut 
mass is not to be compared with animal pus." 



The whole title of Meyen's "Plant Pathology" really reads : — "Hand- 
buch der Pflanzenpathologie und Pflanzenteratologie" edited by Dr. Chr. 
Gottfr. Nees v. Esenbeck. Vol. I, "Plant Pathology." According to this, 
a second part, Teratology, was to be expected. Meyen himself intended to 
work up such a volume, but, according to the Editor, left no material for it. 
Just as Nees v. Esenbeck was about to undertake this himself, there appeared 
tlie "Elements de Teratologic vegetale, au Histoire abregee des anomalies de 
I'organisation dans les vegetaux ; par A. Moquin Tandon, Doct. scienc. et 
med. etc., director du jardin des plantes de Toulouse. Paris 1841." C. F. 
Jaeger "Ueber die Missbildungen der Gewachse" (1S14) and Thomas Hop- 
kirk. "Flora Anomala" (1817) should be mentioned as forerunners of this 
work. We learn from the German translation of Moquin Tandon's^ book, 
that the translator, C. Schauer, was able, as specialist, to call attention to 
many misunderstandings and errors made by the author, especially in the 
German citations and to make additions from his own observations. Moquin 
Tandon says, "By the expression 'malformations', 'monstrosities' (monstra) 
is generally understood innate, more or less important and complicated vari- 
ations from the type of a species, which are disfigurations and oppose the 
regular course of a functioning by hindering or arresting it." We are better 
satisfied by de Candolle's definition (Theor. element. I. ed. p. 406), by which 
monstrosity is any disturbance in the economy of a plant, which is followed 
by a change in organic form and arises from an internal disposition, almost 
never from a visible cause. Moquin Tandon's book is still indispensible to 
every specialist because of its admirable bibliographical references. 



About this time, the science of infectious diseases received a new im- 
petus because of the rapid spread of the potato disease which is still worthy 
of especial attention. It is one of the most dreaded enemies of agriculture, 
and is described in the text books as potato Phytophthora rot. We owe one 
of the first publications on this subject to Martins- and from that 



1 Pflanzenteratologie. Lehre von dem regelwidrigen Wachsen und Bilden der 
Pflanzen. By A. Moquin Tandon. Translated and supplemented by Dr. J. C. 
Schauer. Berlin 1842. 

2 Die Kartoffelepidemie der letzten Jahre. Miinchen 1842. 



58 

time on a flood of publications, proportionate to the very severe injury to 
national property from these diseases. We will emphasize among these pub- 
lications only those of Focke\, Payen-, Schacht", Speerschneider^, v. Holle\ 
Kuhn" and de Bary^ (Further bibligraphical references may be found in 
the detailed discussions of the different diseases). 

It was natural that a phenomenon, such as the potato epidemic, would 
necessarily bring fungous diseases into prominence and increase the whole 
study of mycology. At the same time the economic importance of smut 
fungi also began to receive greater and greater consideration. Tillet^ Tes- 
sier^, and Prevost^", had early studied the smut of grains and at present we 
have accjuired a considerably extended insight into the nature of those dis- 
eases and also into the means of combatting them from de Bary's^^ investi- 
gations and Bref eld's studies, extending over many years. The prevalence 
of smut diseases has led to the development of the sterilization of seed. 

In the second volume of this work, which treats of parasitic diseases, 
the overpowering number of mycological works will be mentioned, — we will 
here mention only some of the most important ones, treating of fungus 
families as a whole. Elias Fries' great work completed in 1832, has already 
been considered. In 1831 the first part of Wallroths "Kryptogamenflora"^^ 
appeared and in 1833 the second part. In this book the cryptogams 
were worked up by Math. Joe. Blufif and Carl Ant. Fingerhuth. In 1842 
Rabenhorst's "Kryptogamenflora"^^ began and in 1851 Bonorden's "Hand- 
buch der Mykologie"^*, which has proved to be very useful because 
of its cuts of microscopic fungus forms, although these had been 
sufificiently considered in the illustrations of Schaffer, Persoon, Greville, 
Sowerby, Sturm, Krombholz and Nees sen. To be sure Corda's "Icones 
fungorum" had already been published and his "Anleitung zum Studium der 
Mykologie"^^ which is provided with very small drawings; leaving the 
peculiarity of his classification out of the question, however, Corda limit- 
ed himself to the easily visible developmental stages, while Bonorden sought 
to determine the tissue structure. This author, in opposition to Unger, em- 
phasized the fact that parasitic fungi are unquestionably independent organ- 



1 Die Krankheit der Kartoffeln im Jahre 1845. Bremen 1846. 

2 Les maladies des pommes de terre, des betteraves, des bles et des vig-nes. 
Paris 1853. 

sSchacht, Bericht iiber die Kartofflepflanze und deren Krankheiten. Berlin 1854. 

4 Das Faulen der Kartoffelknollen. Flora 1857. Bot. Z. 1857. 

5 Ueber den Kartoffelpilz. Bot. Zeit. 1858. 

6 Die Krankheiten der Kulturgewachse, ihre Ursachen und Verhutung. Berlin 
1858. 

T Die Kartoffelkrankheit. Leipzig 1861. 

8 Dissert, sur la cause qui corrompt les graines de ble, 1755. 

9 Traite des maladies des graines, 1783. 

10 Memoire sur la cause de la carie des bles, 1807. 

11 Untersuchungen liber die Brandpilze. Berlin 1853. 

12 Flora cryptogamica Germaniae auctore Ferd. Guil. Wallrothio, Med. et Chir. 
Doctore etc. Norimbergae 1831-33. 

13 Kryptogamenflora von Deutschland, Vol. I., Leipzig 1844. 2nd Edition. I-VII. 
1884-1903. 

14 Handbuch der Allgemeinen Mykologie etc. with 12 plates. Stuttgart 1851. 
If* Anleitung zum Studium der Mykologie nebst kritischer Beschreibung aller 

bekannten Gattungen. Prag 1842. 



59 

isms, but maintained that "it is the stomata which take up the spores and 
bring them to development in the air cavities connected with them." He said 
that algae, hchens and mosses which have no stomata and, for the same rea- 
son, young branches and twigs are free from parasites. He expresses his 
point of view in regard to the action of parasites, as follows : — "That they 
6rst cause an hypertrophy and degeneration of the parts heavily infested with 
them but when isolated they do not disturb the growth of the leaves." Ac- 
cording to him, dry weather is essentially propitious for the spread of the 
parasites, "because it favors the scattering of the spores. On this ac- 
count Caeoma and Phragmidium are never found more abvuidant than in 
dry summers, as also the Caeoma ccrcalium, the yellow corn smut so in- 
jurious to seeds, which caused such great damage in 1846." 

Kiihn in his "Krankheiten der Kulturgewachse" (Berlin 1858) attained, 
in the happiest manner, the end for which Meyen strove, viz. of uniting 
scientific studies with practical experience in the treatment of plant diseases. 
However necessary and important purely scientific investigations may always 
be in phytopathology, yet they achieve their full significance only by being 
tested in practical agriculture. Only by practical work can it be decided 
vvhether the conditions of nature and of the laboratory favor the develop- 
ment of the same parasites or other excitors of disease. So it is necessary to 
build phytopathology upon a practical knowledge of agriculture and horti- 
culture. The dififerences which have developed in medicine between 
the scientific investigator and the practicing physician must also necessarily 
arise in the science of plant diseases. We term this practical side, — the pro- 
fession of "Plant Protection.'" 

Mycological studies are a part of the indispensible fundamentals of plant 
protection and for this reason, we have given them the greatest possible at- 
tention in the history of phytopathology. Continuing with this in view we 
will name first of all the masterly plates in the book by the brothers Tulasne 
"Selecta fungorum carpologia," Paris. The English work by Berkeley 
"Outlines of British Fungology," London i860, is most welcome as a col- 
lective work although it is mostly provided with very rough illustrations. 
De Bary's works continue to be of especial value. His results in this con- 
nection may be found summarized in the "Morphologic und Physiologic der 
Pilze, Flechten und Alyxomyceten," Leipzig 1866. 

We owe further important investigations to O. Brefeld, in his "Unter- 
suchungen iiber die Schimmelpilze," Leipzig 1871, 1872 and following, and 
Cohn for his "Biologische Mitteilungen iiber Bakterien," Schlesische Ges. f. 
\aterl. Kultur, 1873, as well as for his "Untersuchungen iiber Bakterien" 
1875 and for other studies contained in his "Beitrage zur Biologic der Pflan- 
zen." In these Cohn has successfully advanced the history of the develop- 
ment of Bacteria. His pupil, Zopf, essentially extended these studies in the 
work "Die Spaltpilze," Breslau (3rd Ed. 1885). Among the summaries of this 
time mention should be made of Eidam "Der gegenwartige Standpunkt der 
Mykologie mit Riicksicht auf die Lehre von den Lifektionskrankheiten," 



6o 

Berlin (2nd Ed. 1872) and further Winter, "Die Pilze Deutschlands, Oester- 
reichs und der Schweiz," Leipzig 1884. Rabenhorst's "Kryptogamenflora" 
brings the subject to completion. 

The most comprehensive systematic summary of all the fungi is con- 
tained in P. A. Saccardo's "Sylloge Fungorum." The eleventh volume with 
a "Supplementum universale" was published in Pavia in 1895. Sydow's "In- 
dex universalis et locupletissimus nominum plantarum hospitium speciarum- 
que omnium fungorum," Berolini, Fratres Borntraeger 1898, carries the work 
further. This book contains all the fungi known up to 1897. Further sup- 
plemental volumes (XIV-XVI) were published in 1899-1902 and others arc 
to follow. Saccardo supplemented this great work on fungi with 1500 illus- 
trations which were published from 1877-1886 under the title "Fungi italici 
autographice delineati," Patavii. 

In place of the sketchy drawings of this work, A. N. Berlese began to 
publish a series of most careful, colored illustrations under the title, "Icone^ 
fungorum ad usum Sylloges Saccardianae adcommodatae," Abellini. The 
Sphaeriaceae Hyalo phragmiae were furnished in parts IV-Y, which appeared 
in 1894. To our knowledge, the author had not finished the work at the time 
of his untimely death. In the same way, we find colored illustrations in 
Cooke's "Mycographia seu Icones fungorum," London : — the first part ap- 
peared in 1879 with cuts of the discomycetes. 

The publications on fungi and bacteria now become so numerous that 
they are no longer to be mastered and make any further citations impossible. 
This compels us to refer to the "Botanischer Jahreshericht" which has been 
appearing since 1873. 

It is natural that Teratology has also developed further since Moquin 
I'andon. Among the works treating of the material as a whole, emphasis 
should be laid on M. Master's "Vegetable Teratology," London 1869 and O. 
Penzig, "Pflanzenteratologie," systematisch geordnet, Genua 1890-94, which 
may be designated as the most complete book of reference on this subject. 

Because of limited space we must forego all further citations of my- 
cological literature. The reader will find the desired supplementary infor- 
mation in the second volume of this work. However, a brief reference to 
the numerous publications descriptive of fresh and herbarium material must 
be made in a presentation of the history of the development of this science. 
Among the herbaria which pay especial attention to plant diseases, there 
should be mentioned here, F. v. Thiimen, "Herbarium mycologicum oeco- 
nomicum," Teplitz, 1873-79, Rabenhorst, "Fungi europaei exsiccati" con- 
tinued by Winter and Patzschke; L. Fuckel, "Fungi rhenani exsiccati," 2nd 
Edition 1874; Jak. Eriksson, "Fungi parasitici scandinavici," Stockholm 
1882-1895 ; G. Briosi et F. Cavara, "J funghi parassiti delle piante coltivate 
ed utili essicati, delineati e dcscritti," Pavia, fasc. I-XII (1897) ; W. Krieger, 
"Schadliche Pilze unserer Kulturgewachse," fasc. I. 1896; A. B. Seymour 
and F. S. Earle, "Economic Fungi, Cambridge. Following in close connec- 
tion with Rehm's ascomycete collection, published many years ago, are many 



6i 

Herbaria representing the general fungus flora of different countries, as, 
for example, those by Saccardo, Sydovv, Vestergren, J. B. Ellis, Jaap, Bubak 
and Kabat, Posch etc. 



Although the science o"f plant diseases would refer to teratological phe- 
nomena only when it can prove, or at least suppose as a cause of the indi- 
^ idual phenomena, some definite disturbance of nutritive or structural con- 
ditions, it has been forced to take the animal world more and more thor- 
oughly into consideration. The following publications summarize the entire 
material or the larger part of it, are comprehensive and should be used for 
further study : — Ratzeburg, "Die Forstinsekten," Berlin 1839-1844 and "Die 
Waldverderbnis," Berlin 1866-1868; A Gerstacker, "Handbuch der Zoolo- 
gie," Vol. II., Arthropoden, Leipzig 1863 ; E. L. Taschenberg, "Entomo- 
gie fiir Gartner und Gartenfreunde," Leipzig 1871, and "Die der Landwirt- 
schaft schadlichen Insekten und Wiirmer," Leipzig 1865. Further Nordlinger, 
"Die kleinen Feinde der Landwirtschaft," Stuttgart 1869. Kaltenbach. "Die 
Pflanzenfeinde aus der Klasse der Insekten," Stuttgart 1874, and Ritzema 
Bos, "Tierische Schadlinge und Niitzlinge," Berlin 1891. The "Handbook of 
the Destructive Insects," by C. French, published in Melbourne in 1891 by 
order of the Department of Agriculture of Victoria, is less rich in material but 
better adapted to the practical needs of the layman, because of its colored 
plates. 

In the same year H. R. v. Schlechtendal published a smaller special work 
on gall formations, — "Die Gallbildungen (Zoocecidien) der deutschen 
Gefasspflanzen," Zwickau 1891. Ten years later G. Darboux and C. Houard 
jjublished a comprehensive systematic work, — "Catalogue systematique des 
Zoocecidies de I'Europe et du Bassin mediterraneen," Paris 1901. 

The "Forstliche Zoologie" by K. Echstein, Berlin 1897, may be 
especially recommended because of many careful original drawings. The 
popular writings of H v. Schilling are especially useful for horticulture ; 
we recommend "Die Schadlinge des Obst-und Weinbaues," "Die Schadlinge 
des Gemiisebaues," Frankfort a. O. 1898 and the "Practischer Ungezieferk- 
alender," Frankfurt a. O. 1902. The "Schutz der Obstbaume gegen feind- 
liche Tiere" by E. L. Taschenberg (3rd Edition by O. Taschenberg), Stutt- 
gart 1901, is also well adapted for practical needs. 

As the science of plant protection develops there is a corresponding at- 
tempt to produce reference books treating some of the most important culti- 
vated plants, such as Eisbein "Die kleinen Feinde des Rlibenbaues, 1882, with 
carefully prepared colored plates and Emile Lucet "Les insectes nuisibles 
aux Rosiers sauvages et cultives en France," Paris 1898, with numerous 
plates in black and white. Most complete is the work being done in the 
United States in protecting plants from these animal enemies. The Zoolo- 
gists in the several State Experiment Stations and the "Bureau of Entomol- 
ogy" of the Federal Department of Agriculture in Washington, are advanc- 
ing rapidly the study of the enemies of cultivated plants, by new investiga- 



tions and by the distribution of popular treatises. More detailed references 
to zoological literature are to be found in the third volume of this manual. 

The number of text-books and manuals of phytopathology has grad- 
ually been increased since the publication of Kiihn's "Krankheiten der Kul- 
turgewachse," as the understanding of the national economic significance of 
phytopathology has increased. First of all comes Orstedt's "Om Sygdomme 
hos Planterne, som foraarsages af Snylteswampe, navnlig om Rust og 
Brand," Kjobenhavn 1863. This work was followed in 1865 by later reports 
on the alternation of hosts by rust fungi (Gymno sporangium Sabinae). 
About this time Hallier's^ book appeared which must be given more 
especial attention in a history of plant diseases because of the author's stand- 
point. Hallier's views leading to sharp literary disagreements, especially 
with de Bary, may be found in extenso in his later writings-. In his 
"Festkrankheiten der Kulturgewachse," he gives a list of investigations on 
the Peronosporeae and believes he has permanently established by these 
the correctness of his "Plastiden Theory." At the time of the "Cholera 
meeting" in Weimar (1868), Hallier first made the assertion that the forms, 
summarized as Fission fungi (Schizomycetes) by Nageli were not indepen- 
dent organisms, but represent the products of the plasma of diiTerent groups 
of filament fungi. Hence Nageli's family of the Fission fungi should be 
stricken out of the classification and infectious diseases as a whole be traced 
back to the action of such plasma-products ("Plastiden"). "In order there- 
fore to discover the origin of infectious diseases, it is necessary in every case 
to ascertain by investigation which definite fungus produces the cells of con- 
tagion from its plasma (bacteria, micrococcus etc.) and in what way this 
takes place." In regard to the potato disease produced by Phytophthora, he 
does not question whether this fungus is the cause of the disease, but only 
whether it may cause it less directly than would bacteria. "I have proved 
first and foremost that the bacteria which are the absolute cause of the pota- 
to pest, are produced by the "Plastiden" of the Phytophthora and that these, 
when once formed, are absolutely equal to the production of the plague; that 
there is no further need of the mycelium and buds of the Phytophthora." 
His numerous experiments ultimately led him to the view that, in all in- 
fectious diseases, human, animal and vegetable, three main points undoubted- 
ly come under consideration: (i) The absolute cause; (2) External or 
general furtherance (chance causes or predisposition) ; (3) Personal fur- 
therance (susceptibility of the diseased individual). 

Sorauer in the first edition of his "Manual of Plant Diseases," Berlin, 
Paul Parey, 1874, first introduced into plant pathology the view, that in all 
diseases not only the direct cause but also the earlier preparatory stages and, 
in parasitic attacks, the accessory conditions favoring the development of the 
parasites, including the disposition of the host organism, should be taken 



1 Phytopathologie. Die Krankheiten der Kulturgewachse. Leipzig 1868. 

2 Die Plastiden der niederen Pflanzen. Leipzig 1895. — Die Pestkrankheiten 
(Infektionskrankheiten) der Kulturgewachse. Stuttgart 1895. 



63 

into consideration. This statement was definitely established in the second 
edition (1886) and in an abstract written especially for the practical agri- 
culturalist, "Die Schiiden der einheimischen Kulturpflanzen," 1888. The 
delayed acceptance of these ideas is shown by the text-books which im- 
mediately followed. Of these the one especially valuable because of its num- 
erous personal investigations is "Lehrbuch der Baumkrankheiten" by Robert 
Hartig, Berlin 1882 (2nd Ed. 1889). The third edition, in which the 
author rather unreservedly acknowledges a predisposition and differentiates 
local, temporal, individual, acquired and morbid predisposition, appeared in 
1900 with the title "Lehrbuch der Pfllanzenkrankeiten" — Berlin, Julius 
Springer. A study of the phenomena of the decomposition of wood, with 
the title "Wichtige Krankheiten der W^aldbaume," Berlin 1874, is an intro- 
ductory work for this textbook. 

Sorauer's Manual was followed first by Frank's detailed elaboration, 
"Die Krankheiten der Pflanzen," Breslau 1880 (2nd Ed. 1895). The 
"Lehrbuch des Forstschutzes" by H. Nordlinger, Berlin 1884, is devoted 
especially to cultivated forest plants. Solla's book, "Note di Fitopathologia," 
Firenze 1888, is more comprehensive and contains an atlas. This was pre- 
ceded in Norway in 1887 by Brunchorst's "De vigtigste Plantesydomme." 
To this decennium belongs also a number of noteworthy articles by Jensen, 
among which (according to Rostrup) is: "Kartofifelsygen kan overvindes 
ved en let udforlig Dyrkningsmaade," Kjobenhavn 1882. 

While up to this time scientists had classified diseases according to their 
proved or assumed causes, Kirchner in 1890 published "Die Krankheiten und 
Beschadigungen unserer landwirtschaftlichen Kulturpflanzen," Stuttgart, 
arranged especially for practical use. The diseases are listed here ac- 
cording to the different cultivated host plants and described according to 
their visible habit of growtli. Systematic scientific supplements are collected 
at the end of the book. In accordance with the line of investigation of this 
author there appeared in 1895 a richly illustrated book treating of parasitic 
diseases only, — "Pflanzenkrankheiten, durch kryptogame Parasiten verur- 
sacht," by Karl, Freiherr v. Tubeuf, Berlin, Julius Springer. Parastism was 
here developed as a form of sym.biosis and thereby referred to an "internal 
and an external" predisposition for becoming diseased. The internal predispo- 
sition depends on "the energetic condition of the living protoplasm of the host 
cell," while the external one "is determined especially by anatomical condi- 
tions." In the same year Prillieux published a two volume work abounding in 
personal investigations, "Maladies des plantes agricoles et des arbres fruitiers 
ct forestiers," Paris. This, the most comprehensive work in French on the 
subject, describes only parasitic diseases. They are treated scientifically and 
yet the practical side receives attention in so far as means for combatting 
disease are considered. 

An unlooked-for advance in the studies on bacteria resulting from their 
many-sided economic significance, made a revision and enlargement of de 
Bary's "Vorlesungen iiber Bakterien," necessary. In 1900, in Leipsic, Mig- 



64 

ula, enabled by his own work, produced a new edition to wliich he added 
exact bibligraphical citations. 

Meanwhile, as the necessity of familiarizing practical circles with the 
nature of plant diseases became increasingly more evident, it led the large 
German Agricultural Society to undertake the issuing of suitable publica- 
tions. In 1892 appeared the first edition of Sorauer's "Pflanzenschutz," and 
in 1896 its second edition, revised by A. B. Frank and P. Sorauer. The 
authors strived for the briefest presentation possible, classified the diseases 
according to the host plants and treated each disease under three headings : — 
Recognition, Production and Control. The text was supplemented by num- 
erous illustrations on colored plates. In the same way, Frank published a 
more detailed work with the title : — "Kampfbuch gegen die Schiidlinge un- 
serer Feldfriichte," Berlin 1897 and Sorauer one, entitled, "Schutz der Obst- 
baume gegen Krankheiten," Stuttgart 1900, provided with numerous figures 
in the text. 

Of books in foreign languages, there appeared about this time, W. 
Kriiger's treatise on the diseases of sugar cane in the "Bericht der Versuchs- 
station fiir Zuckerrohr in West-Java, Kagok-Tegal," published in 1896. This 
treatise took up thoroughly the Sereh disease with a conscientious use of the 
pertinent literature. Subsequent to it appeared in Leyden in 1898, H. Wak- 
ker and G. Went's "De ziekten vom het suikerriet op Ja\a," which should be 
recommended because of its many plates. 

Delacroix treats the diseases of coffee especially in his book, "Les mala- 
dies et les ennemis des Cafeiers," Paris (2nd Ed. 1900). Two years 
later D. McAlpine, in Melbourne, published "Fungus diseases of stone-fruit 
trees in Australia." 

The last named publication considered cultivated plants only. The need 
of a comprehensive treatment of the whole field of diseases was shown and 
after a long interval, a response, the manual, "Plantepatologi" Haandbog i 
Laeren om plantesygdomrae af E. Rostrup, was published at Kjobenhavn in 
1902. This book, elegantly gotten up and attractive because of its many 
careful original drawings, lays emphasis on fungous diseases, the known 
number of which the author by his many personal observations, published 
after 1871, had increased. To facilitate the consultation and discovery of the 
dififerent diseases, a list was placed at the end of the book, arranged accord- 
ing to the host plants. 

In 1903 the Japanese published a book which should be considered as a 
significant cultural advance. We have a German translation of this entitled 
"Lehrbuch der Pflanzenkrankheiten in Japan," Ein Handbuch fiir Land- 
und Forstwirte, Gartner und Botaniker. Von Arata Ideta (3rd Ed.) Tokio 
1903). This work is provided with a glossary of technical terms in 
German, English and Japanese and contains 13 plates and 144 text figures 
carried out in fine line-drawings (mostly after German authors). 

In a science like phytopathology, in which the results of all investiga- 
tions are intended for use in practical industry, the need is at once felt of 



65 

making the forms and causes of disease more easily comprehended by the 
layman, by means of colored illustrations. On this account, without regard 
to special works on fungi, we often find the text supplemented by colored 
pictures of the habit of growth. An attempt to present the most important 
diseases in the form of a portfolio with short descriptions of the figures on 
the plates could be undertaken only after a more widely extended under- 
standing of the importance of this branch of knowledge had insured a suf- 
ficient number of purchasers. Accordingly, since 1886, Paul Parey of Berlin 
has issued Sorauer's "xMlas der Pflanzenkrankheiten," of which six folio 
numbers have already been published. The especial care used here, in hav- 
ing the difi'erent colors true to nature, made the price such that the publica- 
tion had a smaller circulation among practical workers than in scientific in- 
stitutes, and accordingly a need was gradually shown for the publication of 
a less expensive work. This appeared under the title, "Atlas der Krankhei- 
ten und Beschadigungen unserer landwirtschaftlichen Kulturpflanzen." 
edited by O. Kirchner and H. Boltshauser and published by Ulmer, Stutt- 
gart. This is now completed in six numbers. INIeanwhile the Deutsche 
Landwirtschafts-Gesellschaft discovered, by its publication of "Pflanzen- 
schultz," that at present the time is ripe for the extension of the knowledge 
of diseases among practical agriculturalists, and that it can be carried through 
most successfully by such brief guides. The society published the third 
edition in 1904, revised by Sorauer and Rorig, with seven carefully pre- 
pared plates. The "Atlas des Conferences de Pathologic vegetale" by 
Georges Delacroix, Paris 1901, should be mentioned as of special service to 
the systematic study of diseases. This gives the most important diseases of 
cultivated plants in 56 plates in black and white. In 1902 Delacroix pub- 
lished by order of the French Agricultural Department a small work, "Mala- 
dies des plantes cultivees," Paris, which was written chiefly for general use 
and is supplemental to the above. 

The most significant scientific advance is the publication of monographs 
covering the separate fields of disease. This method has also appealed 
especially to recent workers in plant pathology. In accordance with the im- 
portance of the disease, thorough study has been devoted to the rust fungi, 
especially of grain. In 1894-95 the German edition of a 463-page work by 
Jakob Eriksson and Ernst Henning was published.— "Die Getreideroste, 
ihre Geschichte und Natur, sowie Mafsregeln gegen dieselben," Stockholm. 
This work, which attracted much attention, appeared as a volume of the 
"Meddelanden fran Kongl. Landtbruks-Akademiens Experimentalfalt," and 
its 13 colored plates show clearly the diseases due to grain rusts. It proves 
the specialization of parasitism in the fungi of grain rusts. Besides this, the 
Avork takes up the discussion of the determinative factors and tests the posi- 
tion, the physical and chemical constitution of the soil, the previous cropping, 
time of seeding etc. 

In 1904, H. Klebahn published an equally careful work with a larger 
field and based on his personal studies, entitled :— "Die wirtswechselnden 



66 

Rostpilze," Versuch einer Gesamtdarstellung ihrer biologischen A/'erhaltnisse. 
Berlin 1904. Gebr. Borntrager. A chronological table gives a list of the 
heteroecious rust fungi discovered since de Bary's first investigations made 
in 1864 with Puccinia graminis. The text treats in the greatest detail and 
with pertinent bibliographical references, gradation of dififerences, limi- 
tation of species, specialization and theory of descent, susceptibility and 
transmission of rust diseases in seed. With this is also discussed thoroughly 
the mycoplasm theory brought forward about 1897 by Eriksson. This point 
has already been discussed (see p. 34). Eriksson's latest studies appeared in 
1904 in the publications of the Schwed. Akad. d. Wissensch. under the title : 
"Das Vegetative Leben der Getreiderostpilze." 

A further important advance in the creation of scientific foundations is 
shown in the "Pathologische Pflanzenanatomie" by Ernst Kiister, Jena 1903, 
published by Gustav Fischer. Guided by the discovery that a distinct sepa- 
ration of the natural forms into normal or abnormal can not be carried out, 
Kiister tests the phenomena from the physiological point of view, i. e. as to 
the functional efficiency of the tissues. "The tissues are prevented from de- 
veloping into functionally efficient, i. e. normal tissues, by influences of some 
kind or functionally efficient tissues undergo subsequent changes in which 
they forfeit entirely or partially their functional ability, or new tissues are 
produced in the plant body of such a nature that its diseased and deformed 
organs either accomplish nothing for the organism as a whole, or less than 
those which we designate as normal." We find in this work a successful 
attempt at presenting the developmental mechanics of the vegetable organism. 



A periodical literature developed along with the attempts to organize 
the protection of plants. The guiding principle was the practical question, 
how the spread of disease and the enemies of cultivated plants may best be 
prevented and how their direct control can be most advantageously accom- 
fjlished. 

This question was considered more closely first in the United States of 
North America, since in 1887 stations were formed by the Department of 
Agriculture for the study of phytopathology and of insects. These most 
active institutes and experiment stations first of all issued annual reports and 
then later special publications of scientific investigations. The report of 
1889^ gives a closer insight into the organization of the service. We 
learn from it that the Phytopathological Division published its investigations 
in a definite periodical "The Journal of Mycology" and also distributed pop- 
ular bulletins of some of the most important diseases. Correspondence con- 
sisting of replies to queries consumes much of the activity of these stations. 
For example, in 1889 the questions sent by practical agriculturalists de- 
manded 2500 replies. These scientists desire chiefly to test results of lab- 



1 Report of the chief of the Division of Vegetable Pathology for the year IS 
Published by the authority of the Secretary of Agriculture, Washington 1890. 



67 

oratory studies by field experiments. With the intention of carrying out such 
practical agricultural experiments, the pathological division has installed cer- 
tain supervising agents. When the results of such experiments, conducted in 
the open in different regions, corresponded sufficiently well, general conclus- 
ions were drawn and the results published as speedily as possible. 

In Germany the first attempt toward organization was shown at the 
Agricultural Congress in Vienna in 1890, where Eriksson and Sorauer 
brought forward a proposition .recommending to the government regulations 
similar to those already carried out in America. With the intention of work- 
ing out a special plan and the development of effective activity, an "Inter- 
nationale phytopathologische Kommission" was formed by representatives 
of all European agricultural countries and Sorauer, as secretary, was com- 
missioned to bring out suitable publications. This furnished an incentive 
for the foundation of the "Zeitschrift fi'ir Pflanacnkrankheiten" the first 
annual series of which appeared in 1891. In the same way the interest in 
establishing experiment stations and similar institutions for the special culti- 
vation and the protection of plants in dififerent countries, was stimulated and 
successful. In iSSo^ Korn-Breslau published in Prussia a very thorough 
report, "Ueber die Begrundung einer wissenschaftlichen Centralstelle 
behufs Beobachtung und Tilgung der Feinde der Landwirtschaft aus dem 
Reiche der Pilze und Insekten." The Imperial Government should have re- 
sponded to such stimuli through the German Agricultural Council. In June, 
1889, Julius Kiihn. through whose endeavors the experimental station under 
IloUrung was established in Halle a. S.. brought this same subject before the 
German Agricultural Society and in 1890 the Society established a "special 
committee for the protection of plants" whose Board of Directors was form- 
ed by JuHus Kiihn, A. B. Frank and P. Sorauer. This special committee estab- 
lished a net-work of information bureaux for practical agriculturalists which 
covered the whole German Empire, and published successive "Annual Re- 
ports from the special conimittee for the protection of plants,"- after Sorauer 
had begun in 1891 a statistical revision of the rusts of grains. 

In 1890 the Phytopathological Laboratory at Paris was opened under 
Prillieux and Delacroix and in Amsterdam on the nth of April, 1891, the 
Netherland section of the International Phytopathological Commission was 
estabhshed. This commission called Ritzema Bos to Amsterdam in 1895 as 
director of the "Phytopathologisches Laboratorium Willie Commelin 
Scholten." In this year, at the instigation of the Holland Phytopathological 
Association and of the Phytopathological Division of the Botanical Society 
Dodonaea, the "Tijdschrift over plantenziekten," edited by J. Ritzema Bos 
and G. Staes was published. Meanwhile, an experimental station was found- 
ed at the Pasteur Institute for the purpose of combatting injurious animals 
by means of contagious diseases. In 1894 this was placed under the direction 
of Metschnikoff. As director of the "Experimentalfaltet" at Albano, near 
Stockholm, Eriksson was untiringly active. In 1895 he published test ex- 

1 Archiv des Deutschen Landwirtschaftsrates, Part 8, p. 307. 

2 Jahresberichte des Sonderausschusses fiir Pflanzenschutz. 



68 

amples for the special forms of grain rusts after which, in February 1901, 
the State granted him a fund of io,ocxd Kronen because of these studies. 
The question of rust which is also of the highest significance in Australia 
led in 1888 to the annual meeting of a Congress of Members of the Austra- 
lian Colonies which, for a considerable number of years, published an official 
report, "Rust in wheat Conference." 

In Germany, Sorauer's "Zeitschrift fiir Pflanzenkrankheiten" was fol- 
lowed in 1892 by C. v. Tubeuf's Forstlich-natiirwissenschaftliche Zeit- 
schrift" which devoted especial attention to plant diseases. In 1898 the"Kgl. 
bayrische Station fur Pflanzenschutz" was founded with von Tubeuf as di- 
rector. Besides this, reports in the collective work, "Just's botanischer Jah- 
resbericht," published since 1873, became much more abundant, since a 
greater number of periodicals now included the subject of plant diseases in 
their programs. Among these belongs first of all the "Centrolblatt fiir Bak- 
tcriologic, Parasitcnkwidc und Infektionskrankhciten" issued by Uhlworm 
and Hansen, as also "Hedwigia," edited by Hieronymous and P. Hennings, 
the "Botanische Centralhlatt," elaborated by Lotsy, also Biedermann's 
"Centralblatt fiir Agricvdturchemie," edited by Kellner, the "Naturwissen- 
schaftliche Zeitschift fiir Land-und F orstwirtschaft" by von Tubeuf and L. 
Hiltner and the "Practische Bliitter fiir Pflanzenhau und Pflanzenschutz" 
by L. Hiltner. We find thorough reports, especially on tropical cultivated 
plants, in "Tropenpflanzer" Zeitschrift f. tropische Landwirtschaft, by O. 
Warburg and F. Wohltmann as well as in its "Beiheften" (supplements) 
which form the organ of the "Kolonialwirtschaftliches Komitee zu Berlin." 
In the German East- African colonies, Zimmermann is especially active in 
pathological fields as is shown by his "Mitteilungen aus dem biologisch-land- 
wirtschaftlichen Institute Amani" In Austria the "Zeitschrift fiir das Land- 
wirtschaftliche Versiichszvesen in Oesterreich" was founded in 1898. In the 
following year P. Nypels began a series of publications under the title "Mal- 
adies des plantes cultivees" Bruxelles. In 1900, v. Istvanfii published the first 
volume of the "Annales de ITnstitute Central ampelologique Royal Hongrois" 
as the report of the Central Vineyard Institute which had been placed under 
his direction. Here also especial attention was paid to diseases. The same 
is true also of the "Jahresberichte der Kgl. Lehranstalt fiir Obst-,Wein-und 
Gartenbau" published by Gothe and later by Wortmann in Geisenheim a. Rh. 
and the annual reports of the "Ueutsch-schweizerische Versuchsstation fiir 
Obst-Wein-und Gartenbau zu Wadensweil," Ziirich, revised by Miiller- 
Thurgau. 

This list of periodicals which in part review German and foreign litera- 
ture and in part publish original articles, gives an insight into the unusually 
rapid growth of material which necessarily demands a unified summary in 
some collective work. Hollrung devoted himself to the working out of such 
a summary and since 1899 has been publishing a "Jahresbericht iiber die 
Neuerungen und Leistungen auf dem Gebiete der Pflanzenkrankheiten," 
Berlin, publishing house of Paul Parey. 



69 

Thus the new science of phytopathology has taken to itself the same 
literary methods which the older branches of knowledge use and which are 
undisputably necessary for scientific progress. But the practical side of 
phytopathology, viz., the protection of plants, has also found a desired de- 
velopment. The idea of establishing special institutions, suggested in 1880 by 
Korn, actively advocated in 1889 by Kiihn and further developed by Sorauer 
at the International Agricultural Congresses and in the "Zeitschrift fiir 
l^flanzenkrankheiten" was brought in 1891 to general attention in the Pruss- 
ian Abgeordnetenhause (Chamber of Deputies) by Schultz-Lupitz in the 
form of a motion. On the 27th day of April of the same year the "Reich- 
sanzeiger" gave out that the motion of Schultz-Lupitz had been referred to 
the Royal State Administration for discussion and at once the Department 
of Agriculture attempted to^ test the question in how far the production of 
plants could be advanced by the enlargement of the scientific institutions sub- 
ordinate to that purpose. As the question received a more thorough- con- 
sideration, it became evident that the best interests of the protection of plants 
could only be had from an Imperial Institution. Such was now formed in 
connection with the Imperial Board of Health as a "T^iologische Abteilung 
fiir Land-und Forstwirtschaf t" and since 1905 this has been an independent 
institution of the Empire. The department, at present under Aderhold's di- 
rection, possesses in Dahlem, besides the proper laboratories, a very expensive 
experimental field and has published its results at indefinite intervals since 
1900. Besides these scientific works the "Biological Division" also pubhshes 
popular bulletins and colored posters and in this way promotes the knowledge 
of the most abundant animal and vegetable agencies injurious to plants. In- 
formation as to their control is also distributed gratis, directly to these 
workers. 

Besides the above mentioned imperial institution which now bears the 
title, "Kais. Biologische Anstalt fiir Land-und Fortszvirtschaft," we find in 
the different German States many organizations for the furtherance of plant 
protection, which in part are associated with the already existing high 
schools and experiment stations and in part are independent establish- 
ments. Among these, besides the institutions already mentioned at Halle 
and Geisenheim, there should be named also the Anstalt fur Pflansenschuts 
in Hohenheim, founded in 1902 and now under the direction of Kirchner. 

We also find in the other European countries an active development of 
the study of plant diseases, proved by the publications of many institutions. 
Among these belong the "Bulletin de la Station Agronomique de I'Etat a 
Gembloux," Bruxelles (Em. Marchal), and "Travaux de la Station de path- 
ologic vegetale," by Delacroix, Paris, the "Tijdschrift over Plantenziehten" 
(Ritzema Bos) already mentioned and the "Landbouwkundig Tijdschrift," 
the "Oversigt over Landbrugsplanternes Sygdomme" Kjobenhavn, in the 
"Tijdsskrift for Landbrugets Planteavl," Kjobenhavn (Rostrup), the "Upp- 
satser i praktisk Entomologi," Stockholm (Lampa). "Beretning om Skadein- 
sekter og Plantesygdomme," Kristiania (Schoyen). "Berattelse ofver skad- 



70 

einsekters upptradande i Finland" (E. Retiter), in the "Landbruksstyrelsens 
meddelanden," Helsingfors, the "Annual report of the consulting botanist" 
(Carruthers) in the "Journ. Royal Agric. Soc," London. 

It is a matter of fact that countries outside of Europe have not been 
backward in the endeavor to increase plant protection. This branch of 
knowledge has been most advanced in North America where the Department 
of Agriculture at Washington has devoted special attention as well to animal 
enemies. Besides establishing the "Division of Entomology" which, by its 
valuable investigations, contributes essentially to the knowledge of animal 
injuries, the organization of meetings of agricultural zoologists is especially 
noteworthy. In these meetings questions of general significance are dis- 
cussed. Besides this, many investigators in the Universities and Experiment 
Stations are working along these lines with gratifying results. Of the latter, 
we will mention the Agricultural Experiment Station of the State of New 
York at Ithaca and the New Jersey Agricultural College Experiment Station. 
Further statements are made in our detailed exposition in which the different 
bulletins of the institutions for the advance of plant protection are 
mentioned. 

Besides the numerous publications of the United States of North Ameri- 
ca, the magazines of other countries also furnish noteworthy contributions 
to the knowledge of the diseases of cultivated tropical plants. Among them 
belong the "Mededeelingen van het Proefstation voor Suikerriet in West 
Java," the reports of the "Proefstation voor Cacao to Salatiga," Malang, the 
"Boletim da Agricultura," S. Paulo, "Boletim del Instituto Fisico-Geograph- 
ico de Costa Rica," "Queensland Agricultural Journal," "Australian fungi" 
(McAlpine), in the "Proceed. Linnean Society of New South Wales," "Ad- 
ministration Reports, Royal Botanical Gardens," Ceylon, "Report of the De- 
partment of Land Records and Agriculture," Madras, and "The Journal of 
the College of Science, Imperial University of Tokio," Japan. We must 
refer to the "Botaniker-Adressbuch" by J. Dorfler, Vienna, 1902, for the 
numerous other institutions and individaul investigators. 



APPENDIX. 

In the above statements we have mentioned not only the literature on 
the subject but also given expression to the leading ideas of the different 
periods in order to show how the science has gradually developed to its 
present standpoint. To be sure, changes in the points of view on the nature 
and role of parasitic organisms are not without interest, but no less interest- 
ing are the references of the various authors to the influence of the stars, i. e. 
the atmospheric factors, which may be traced as a red line through all the 
reports. On this account we have often restated at length the earlier points 
of view and find a striking agreement with the oldest periods since emphasis 
is always laid on the dependence upon climatic and soil conditions and in part 



71 

also upon cultural habits of those phenomena, which we have learned to 
recognize as parasitic. 

This idea, which is also the guiding principle in the present book, has 
led the author to undertake the first experiments for collecting the Statistics 
of Plant Diseases. These experiments which, as already mentioned, were 
begun with the help of the German Agricultural Society and continued by its 
"Special Commission for Plant Protection," have now found recognition, 
for the "Kais. Biologische Anstalt fiir Land- und Fortswirtschaft" beginning 
with 1905 has assumed the collection of statistics of plant diseases. 

Doubt is often expressed as to the importance of such statistics for our 
subject and reference made to the fact that our most dangerous diseases are 
constantly present and the statements of the statisticians concerning the 
intensity of the attack and the amount of agricultural loss appear to 
be influenced so individually that all certain positive figures can never 
be attained. In opposition, it should be emphasized that I did not undertake 
the collection of statistics in order to obtain precise figures as to the dis- 
tribution and agricultural effect of the diflferent diseases. (Besides, in this 
connection, the making of reports will gradually, with the increased educa- 
tion of the body of observers, become as exact as it is in all provinces of 
organic life). The chief undertaking in the collection of statistics lies in the 
proof of the relations which the different diseases bear to climatic and soil 
conditions felt locally or universally, as well as to cultural factors. The study 
of the extreme forms of disease, easily verified, and the determination as to 
which factors have produced these extreme forms makes up the productive 
field of the statistics. 

In these studies lies the future of patholog}^ 

However valuable in themselves the observations as to the formal po- 
sition and the life requirements of the parasitic micro-organisms may be, 
nevertheless, they form only one link in the chain of investigations and be- 
come important only in the determination of their relation in nature and in 
the usual practice of agriculture. And this we can recognize by means of a 
carefully arranged statistical office showing the conditions governing the in- 
crease or decrease of diseases. 

This knowledge leads to the prevention of diseases by means of an ever- 
developing plant hygiene and plant pathology must develop further in this 
direction in the future. 



DETAILED EXPOSITION. 



SECTION I. 
DISEASES DUE TO UNFAVORABLE SOIL CONDITIONS. 



CHAPTER I. 
THE LOCATION OF THE SOIL. 

Even if the diseases which are due to an unfavorable location of culti- 
vated land are better understood by means of the different factors because of 
which this position becomes injurious to plant growth, we have still con- 
sidered it necessary to describe in the following section the general conditions 
due to different locations. We have done so because it is of special impor- 
tance to the guiding principle of this manual and to any reference to a pre- 
disposition to certain diseases which is developed from this location of the 
soil that it be shown how the material and formal structure of any plant 
species changes with the condtions of the habitat, how thereby separate func- 
tions may sometimes be suppressed, sometimes advanced, and -how accord- 
ingly the different localities impress their definite characteristics on the plants 
which, on this account, must behave very differently in relation to the differ- 
ent injurious causes. 

I. ELEVATION ABOVE SEA LEVEL. 

a. General Changes in Habitat in Relation to Herbaceous Plants. 

There is no need of discussing further the fact that the temperature al- 
ways falls with an increase in elevation of any cultivated surface above sea 
level and that this fall in temperature is a determining factor for limiting 
vegetation, on which account the time of harvest in mountains must always 
be later than on lower levels. It is an universally recognized fact that this 
later harvest brings with it great difficulties in curing the grain and not in- 
frequently makes necessary special precautions in high m.ountains, and that 
despite these precautions there often takes place a blackening of the grain as 
a result of the beginning of fungous growth. An example with exact figures 



73 

is given by Angot\ according to whose observations the harvest of winter rye 
in France is delayed on an average about four days, as the elevation increases 
about lOO meters. Attention should be called, however, to the circumstance 
that, with increasing height, the air being thinner is less warm so that there- 
fore it must have an appreciable effect on the development of vegetation. 
With this should be reckoned conditions of moisture which, aside from the 
phvsical constitution of the soil, are different for plants of Alpine regions in 
lower latitudes than for those from plains in the Arctic zone. Within the 
same degree of latitude mountains, as colder bodies, will condense more 
water vapor and thereby bring about more abundant precipitation than takes 
place on plains. On this account more snow will fall and the warmth needed 
to melt this greater mass of snow is withdrawn from vegetation. Even after 
the snow has melted in spring, the plants in the mountains will ne\ ertheless at 
first be less able to benefit from the sun's warmth than those on the plains 
since the inequalities of the upper surface of the soil become eft'ective. A 
square meter of very broken ground surface has a much greater upper sur- 
face, divided into many slanting levels, over which the same amount of 
warmth must be distributed, than has perfectly level land, the different par- 
ticles of which are raised to a higher temperature. This is the case in moun- 
tain chains in contrast to level plains. It is evident from these statements 
that with increased elevation above the sea these processes of weathering and 
decomposition must be retarded since they are essentially favored by 
warmth. It is also evident that such peculiar combinations of vegetative 
factors will produce characteristic forms, of which the best known feature 
is short, repressed growtli. Such forms of growth are kept constant, first of 
all, in the seeds. Climatic forms which have become hereditary in this way 
have been termed "Oecolocjical variations"'-. 

If it was said at first that the temperature of the air at higher levels is 
lower, it must also be emphasized, on the other hand, that at higher levels the 
intensity of the illumination increases and produces accordingly greater soil 
zvarmth. On this account climate of the lower and middle latitudes, on ac- 
count of the greater intensity of light and greater warmth of the soil, would 
differ favorably from that of those plains in a Polar zone where the tem- 
perature of the air is the same. The lesser atmospheric pressure in moun- 
tains must result in an increase of transpiration as stated by FriedaP 
and the increased supply of light in an increase of the assimilatory activity of 
the leaf. Consequently the typical mountain plant works more energetically 
and in this way is explained its shortened vegetative period. 

According to the observations of Bonnier-*, who made experimental 
gardens on Mt. Blanc and in the Pyrenees, in Alpine climates with a 



1 Der Naturforscher, 1883, No. 24. 

-' Lebensgeschichte der Bltitenptlanzen Mitteleuropas. Von Kirchner, Loew und 
C. Schroter. Stuttgart, Ulmer 1904. p. 116. 

3 Friedal, Action de la pression totale sur I'assimilation chlorophyllienne. C. rend. 
1901. Cit. Bot. Jahrcsb. 1901. Section II, p. 221. 

i Bonnier, Etude experimentale de I'influence du climat ali)in sur la veg-etation 
etc. Bull. Soc. Bot. France. Vol. XXXV. 35. 1888. 



74 

greater number of herbaceous plants, the shoots became shorter, leading to 
nanism. In specimens from high mountains, the palisade parenchyma is 
more strongly developed and contains more chlorophyll. Accordingly, the 
assimilatory work has been increased. If the leaves of the same species from 
specimens grown on plains and in mountain gardens, are cut off at the same 
time and tested, the leaves from the high mountains showed a stronger de- 
velopment of oxygen in an equal length of time for equally large surfaces. 
It is said that such Alpine characteristics can be artificially bred in plants by 
packing them in ice at night while leaving them during the day under normal 
growing conditions^ 

In a later report, Bonnier- calls special attention to the increase 
in temperature and assimilation which, taking place in Alpine regions, 
may easily account for the fact that plants from the plains, brought into an 
Alpine climate, develop relatively greater amounts of sugar, starch, volatile 
oils, coloring matter, alkaloids and other products of chorophyll activity. 

How greatly this specific climatic character immediately influences the 
mode of development of any plant species is shown by the well-known ex- 
periments on structure carried on from 1875 to 1880 by Kerner v. Marilaun-^ 
with seeds taken from the same parent plant which had been grown 
with precaution against cross-fertilization. Part of the seeds were sown in 
an Alpine experimental garden on the top of Mt. Blaser in the Tyrol (2195 
m. elevation), others in the botanical garden in Vienna. The germination of 
the seed on top of Mt. Blaser took place soon after the melting of the snow 
which had been 1.5 m. deep, between the loth and 25th of June. The 
germination and growth of the seedlings therefore took place when the sun 
was highest and the days longest. The seedlings were exposed at once to a 
temperature which was just as high or perhaps somewhat higher than that 
furnished the experimental plants in the botanical garden at Vienna, when 
the March day was twelve hours long. At the end of August and the be- 
ginning of September blossoms were observed on the plants which had not 
been killed by the several frosts in June, July and even in August, for ex- 
ample, on Satureja hortensis, Lepidium sativum, Agrostemma Githago, Cen- 
faurea Cyanus, Turgenia latifolia etc. 

The plants grown in the Alpine experimental gardens differed from 
those in the botanical gardens at Vienna in that they were strikingly shorter 
and their stems developed a greater number of parts. It was found further 
that in the Alpine specimens, for instance, Viola arvensis, blossoms developed 
even from the axis of the third and fourth leaves while at Vienna they came 
only between the seventh and eighth leaves. The number of blossoms was 
fewer and the petals, like the leaves, were smaller, as a rule. A part of the 



1 Palladin, Onfluence des changements des temperatures sur la respiration des 
plantes. Revue gen. de Botanique, 1899, p. 242. 

2 Bonnier, Gaston, Influence des hautes altitudes sur les fonctions des vegetaux. 
Compt. rend, de I'Acad. scienc. Paris. Vol. CXI. 1890. Cit. Bot. Centralbl, 1891. 
No. 12. 

3 Pflanzenleben. Vol. II, pp. 453 ff. Wein. 1898. 



75 

annual species from the plains which had had sufficient time and warmth to 
develop seeds were longer lived on the top of Mt. Blaser since in the follow- 
ing year, new sprouts were developed from the lower part of the stems. An 
earlier blossoming could also be observed. 

Corresponding to the fact that the intensity of the sunlight increases 
with increased elevation, the color of the blossom, depending upon the antho- 
cyanin, also became more intense. Blossoms, which were white on the plains, 
had in the Alps petals which were violet underneath. The glumes of grasses, 
green on the plains, or only pale violet, became dark brownish violet in Al- 
pine regions because of a more abundant formation of anthocyanin\ 
The leaves of Sedum acre, S. album and S. hexangulare became purplish red. 
On the other hand, leaves of Orohtts vermis, Valeriana PIiu and Viola cnciil- 
lata turned yellow from the excess of light in the Alpine experimental gar- 
dens while in the valley in shaded places their foliage remains green. 

The mountainous region affects not only temperatures in the annual 
seasonal average but especially the moisture content of the atmosphere. 
Warmth and humidity in their total amount and in their distribution during 
the seasons together vvith the supply of light are determinants of growth. As 
already mentioned, atmospheric moisture influences the amount of light 
available for the plant, for a humid atmosphere absorbs about five times as 
many light rays as does a dry atmosphere. 

Since the absolute content of the air in water vapor decreases with the 
elevation, less light will be absorbed in the mountains, especially since the 
rays of light have a shorter distance to traverse in order to reach the earth as 
compared with regions at sea level. The fact that the absolute vapor con- 
tent of the air decreases with the elevation is a matter of course for, since 
the temperature becomes lower and lower, the air must condense its water 
vapor and give it off in a liquid form. But the relative moisture increases 
in the mountains which explains why we call a mountain climate damp and 
rainy. Cloudiness is also relative to the moisture of the air. 

This increase of the relative moisture and the decrease of temperature 
form the reasons for the rapid ending of our cultural eft'orts so far as these 
concern the obtaining of seeds in mountain regions. We know that the for- 
mation of blossoms and seed requires an increase of warmth proportionate 
to the length of the growth period. For this reason we find, as mentioned at 
the beginning, that grain often does not ripen in the mountains and that 
therefore clover and other legumes furnish an insufficient amount of seed. 
Yet another condition must be added to those already mentioned, to which 
Pax has called attention-, viz., that the insects are onlv half as num- 



1 The theory that anthocyanin is developed for the protection of the plant 
against too strong sunlight is held by many investigators. Kerner (1. c. Vol. I, 
p. 508) assumes that, in the reddening of blossoms which appears with a lack of 
heat, the loss to the blossoms of the directly conducted heat is compensated "by the 
heat obtained from the rays of light by means of the anthocyanin." We believe we 
have observed that the red coloring matter indeed does develop abundantly with a 
lack of heat, but can also set in with an abundance of heat if, in proportion to the 
heat, an excess of light makes itself felt in the tissues which contain sugar. 

2 Das Leben der Alpentlanzen. Zeitschr. d. d.-ostr. Alpenvereins 1898, p. 61. 



76 

erous at an elevation of 2300 m. as on the plains. On this account labiate 
plants play a considerable role on high mountains. Also the increased diffi- 
culty of insect fertilization is partly equalized by the fact that an asexual 
reproduction also takes place (Polygonum viviparum, Foa alpina, Saxifraga 
ccrnua) ; further, ten-elevenths of all kinds of small bushes and even Viola 
tricolor, an annual with us, become perennial in the Alps. 

Besides this, reference should be made to the fact that, with unlimited 
cultural experiments at high elevations, short-lived mountain varieties are 
form.ed which, to be sure, furnish seed in smaller amounts but more satis- 
factory in quality. This offers greater possibilities of yielding a good har- 
A'est in the mountains and (according to Schiebler)^ has the advantage 
of retaining at lower levels its shortened period of growth and there- 
fore can be used advantageously in Northern climates. 

Development of the Aerial Axis of Woody Plants. 

In contradiction to a widespread opinion, it should be mentioned, that 
divarf grozvth in high mountains is not to be ascribed to the pressure of the 
snow since we have tree-like forms in those regions where the most snow 
falls. It is known that the snow covering does not become thicker, the great- 
er the elevation of the mountain, but with us increases up to perhaps an 
elevation of 2500 m., that is, only to the upper boundary of the dwarf coni- 
fers, dwarf alders and the Alpine rose. Higher up the amount of precipi- 
tation decreases. Spruces, larches and the cembra-pine suffer less from 
snow pressure when they stand alone or scattered because their elastic, slop- 
ing older branches let the accumulated snow slip off" more easily when the 
wind blows. Other trees, like Salix serpyllifolia and Rhamnus pumila, fre- 
quently escape excessive snow pressure by their growth on steep rocky cliffs 
from which the snow slides rapidly. However, trees exposed to the full 
pressure of the snow can scarcely be made to grow closer to the earth be- 
cause of the burden of the snow or of windy weather. Rather, we may as- 
sume with Kerner that it is the soil warmth which, in the immediate prox- 
imity of the earth, affords them the best conditions for existence. In the 
higher Alpine regions the soil is much warmer than the air which absorbs 
less sunlight on account of its increasing thinness and its rapidly decreasing 
water content. The above quoted author cites that, for example, on the top 
of Mt. Blanc (4810 m.) the intensity of the sunlight is 26 per cent, greater 
than at the level of Paris. On the Pic du Midi (2877 m.) a temperature of 
33.8°C. was observed in the soil on which the sun shone while the air showed 
a temperature of only io.i°C. This warmth of the soil together with the 
intensity of the light explains the speedier development and blooming of 
Alpine plants. 

Vochting-, in opposition to Kerner, thinks, on the ground of his 
observations with Mimulus Tilingii, the young branches of which at a defi- 

1 Schiebler, Die Pflanzenwelt Norwegens. Allg. Teil. Christiania 1873. 
- Vochting, H., Ueber den Einflufs niedriger Temperatur auf die Sprofsrichtung. 
Ber. Deutsch. Bot. Ges. XVI. ]SP8, p. 37. 



77 

nite age incline downward in spring when the temperature is lower and 
straighten up later with increased warmth, that the creeping habit of growth 
of Alpine plants may be ascribed in part or entirely to the influence of the 
low temperature. We can not agree with this theory. 

Rosenthal' made investigations concerning the mode of growth 
of trees in Alpine regions. He found that in all the species of wood studied 
the annual ring is narrower in high countains than in the lowlands. The ec- 
centricity of the branches is usually very great but the direction of the great- 
est increase of growth varies. The vascular system, on account of the in- 
creased evaporation, is more extensively developed. In dicotyledons, a 
higher percentage of the vascular tissue is obtained by a narrower annual 
ring; in conifers there is a considerable decrease of the late wood ring. 

The landslides which continually take place in inountains because of 
storm conditions displace the trees and thereby change their woody develop- 
ment. Hartig- pointed out the formation of broad annual rings and 
so-called "red wood" (wood with short tracheids and strong lignification) 
on the underside of the trunks and branches of the spruce as soon as they 
bend toward the horizontal, while slender annual rings and "strain wood" 
(long tracheids with weak lignification) are formed on the upper side. Ac- 
cording to Giovanozzi'' this difference in the formation of the wood ring 
of conifers is made use of in hygrometric measurements by the inhabi- 
tants of the Piedmontese Alps since the small celled, thin-walled red wood 
possesses hygroscopic characteristics very different from those of the strain 
wood. The red wood side of a peeled branch becomes concave in dry air, 
convex in moist air. 

According to the investigations of Cieslar^ the lignin content of 
spruce wood seems to be less near the upper boundaries of the tree zone than 
in lower positions. 

It will be concluded from Cieslar's' observations, that the suppressed 
growth in Alpine forms is hereditary for the immediately following 
generation, according to which spruces from seeds of trees grown in moun- 
tainous regions grow more slowly when cultivated on the plains than do 
plants raised from seeds of trees from the plains similarly grown. Engler has 
made the same observation in seeding experiments at the forestry experimen- 
tal station in Ziirich. From germination experiments with the seeds of 
spruce, pine and other forest trees, M. ICienitz" concludes that the minimum, 
optimum and maximum germinating temperatures of spruce seed indigenous 
to lower regions are higher than for seeds grown in higher positions. 



1 Rosenthal, M. Ueber die Ausbildung der Jahresringe an der Grenze dea Baum- 
wuchses in den Alpen. Dissect. Berlin, cit. Hot. Centralbl. 1904. No. 43. 

- Hartig, R., Holzuntersuchungen. Berlin. Springer 1901. 

3 Giovanozzi, Sul movimento igroscopico del rami delle Conifere. Malpighia 
XV, cit. Bot. Jahresb. 1901. Sec. II, p. 191. 

•I Cieslar, A., Ueber den Ligningehalt einiger Nadelholzer. Mitt. a. d. Forstl. 
Versuchswesen C)esterreichs 1897. Part XXIII. 

5 Centralbl. f. d. g-esamte Forstwesen, 1894. Vol. 20, p. 145. 

6 Kienitz, Vergleichende Keimversuche mit Waldbaumsamen aus klimatisch 
verschieden gelegenen Orten Mitteleuropas, Ref. Bot. Zeit. 1879. p. 597. 



78 

In plantations in high altitudes, however, it must further be taken into 
consideration that the elevation acts differently according as it presents iso- 
lated peaks or high plateaux. Since the earth's illumination and radiation 
have considerable influence on the temperature of the layers of air covering 
it, vegetation at equal heights is exposed to very diverse temperature fluctu- 
ations. On the high plateau the decrease of warmth with elevation is less, 
when the sun shines, than on the mountain peak which stands alone. If, 
however, the sun disappears and radiation becomes determinative, then the 
lower air layers above the high plateau also cool off more. Thus the daily 
fluctuations in temperature are nivicli greater here and the seasonal ones as 
well. On high plateaux the temperature can fall, even to frost, while the 
isolated peaks remain protected. The same relation is shown between valley 
and heights ; we have recently observed a number of examples from Italy. 
Passerini makes ^ the following observations from the neighborhood of Flor- 
ence and cites, as an especially good instance, the night of April 19-20, 1903, 
when the temperature, which on the 15th still showed -j-i8.3°C. sank to 
— i.i"C. and rose again, nine hours later, to -|-I2.2°C. While the vegetables 
and grains were not injured, the leaves and blossoms were seriously frozen. 
Only 50 m. higher the injuries were no longer noticeable. 

In mountainous regions clouds and mist act as a protection from frosts. 
Thomas^ observed in Thiiringen that the young beech foliage did not 
suffer from frost at heights covered by mists while in the valleys and gorges 
the leaves were injured. The artificial prevention of frost by the production 
of smoke has been founded on the peculiarity of mists which prevents the 
sharp fall in temperature. 

Adjustment of tpie Root Body of Woody Plants. 

In mountains the adaptation of the wood body to the rocky soil and the 
compensatory structures which appear on this account are especially interest- 
ing. In the following figure i, we see the root of an oak which has made 
its way through a fissure in a rock and by its continued growth in thickness 
within the split has developed into a flattened, board-like form. After leav- 
ing the rock, the root resumed its cylindrical form. This example shows 
first that, despite the pressure which the strong root had withstood for so 
many years, the ability to conduct water and plastic material has not been 
interrupted in the board-like part. In the second place, we notice above the 
board-like flattening the appearance of adventitious roots. Both processes 
correspond to the phenomena caused by artificial constriction. 

So far as we have been able to investigate roots which had been flatten- 
ed in, the clefts of rocks, we could observe that the board-like flat places in 
the root body were produced because the wood rings formed every year were 
very strongly developed on the sides where they could develop freely. 



1 Passerini, Sui danni prcdotti alle piante del ghiacciato etc. Bull. Soc. Bot. 
ital. 1903. p. 308. 

2 Thomas, Fr., Scharfe Horizontalgrenze der Frostwirkung an Buchen. Thiir. 
Monatsblatter. April 1904. 



79 



therefore, in the direction of the split surface, but, on the other hand, they 
were reduced to a minimum on the side where the roots were pressed against 
the rock and were finally irrecognizable. On the free side of the wood the 
vascular bundles developed very abundantly, in some annual rings, in fact, 
the wood was very broad and provided with a thick bark ; on the side of the 
root pressed against the rock, the wood lacked all vascular formation, was 
short-celled and formed from wood fibres inclined diagonally instead of 





Fig-. 1. 
Roots of Quercus Pedunculata grown between rocks. 



Fig-. 2. 
(After Dobner-Nobbe.) 



running vertically. Finally, dififerentiation into annual rings could not be 
observed and only a very slender cork layer is seen lying on the occasionally 
formed short-celled parenchyma, without any recognizable differentiation 
into medullary rays. 

Nevertheless, the cambial activity was not lost in the board-like part of 
the root as was evident when the pressure ceased, for the flattened part grew 
normally in its cylindrical form. Anatomical changes in the roots pressed 
between the rocks approximate so strikingly the results obtained by artificial 



8o 

constriction of the aerial axis, that we can refer in this connection to our 
subsequent studies in the chapter on "Wounds." 

Figure 2 shows a different root, also from Quercus pedunculata, which 
probably has only been pressed between stones. In meeting with this ob- 
struction to its growth in length it was bent and. when growing further, be- 
came flattened. With increasing age the pressed root surface again reached 
the open and with the removal of the pressure came an increased formation 
of the wood ring in great luxuriance like callus rolls. The squeezing which 
the roots had undergone, might have acted like girdling and have produced 
in this a kind of girdling roll above the place of pressure. (See Girdling in 
the chapter on "Wounds"). 

We can get an idea as to the anatomical conditions in the first stages of 
such flattening of the root from the investigations of Lopriore\ He 
observed adventitious roots in the germinating plants of Vicia Faba which 
were forced to grow under the lateral pressure of cotyledons which had not 
separated from each other. Within the sphere of pressure these tender roots 
appeared flattened like ril)bons but after leaving the region of pressure, they 
again became normally cylindrical just as was noticd in the oak roots. In 
the very young roots of the horse bean (Vicia Faba) Lopriore found that the 
epidermal cells on the sides not pressed upon by the cotyledons had developed 
into root hairs. On the compressd sides, however, not only the epidermal 
cells were tangentially flattened but also the two or four outer layers of the 
bark were considerably pressed so that they formed a kind of peripheral 
girdle around the root on these sides, whereby the radial walls of these com- 
pressed cells seem folded zigzag as in a bellows. The cells subjected to the 
pressure of the cotyledons were also proved changed materially since their 
membranes either developed into cork or "together with their lumina were 
impregnated with a kind of protective gum." 

We have already called attention to the fact that in figure i several 
adventitious roots had been formed above the board-like flattening. As may 
be seen, th^ root had made a curve here before entering into the split in the 
rock and under the influence of this twisting, a new formation of adventitious 
roots had been started on the free convex side. We perceive in this a result 
of the stimulus of twisting which Noll- has discussed in detail in his 
work. It is easy to observe that roots which have become twisted because of 
a pressure, hindering their growth in length, develop new side roots on 
the convex side at the point of twisting. In water cultures in glass vessels 
this phenomenon may l)e observed when strong roots reach the bottom of the 
vessel and grow against it. 

In mountains emergency precautions are met widi in the flatly growing, 
younger tree roots if the tip of a rootlet has been lost through injury or from 



1 Lopriore, G., Verbanderuns; infolge <ies Kijpfens. 13er. Deutsch. Bot. Ges. 
Vol. XXII, Part 5, p. 309. 

2 Noll, Verg-leichende Kulturversuche. Sitzungsber. d. Niederrhein. Ges. f. Na- 
turkunde. Cit. Bot. Jahresber. 1900. II. p. 304. 



8i 



drying out on the rock. In figure 3a, we see such a compensatory root which 

has been developed above the dead tip of the 
main root A A. The compensatory organ is 
much stronger and fleshier than the side roots 
which had been formed earher. 

The formation of adventitious roots as a 
resuh of the stimulus of twisting or of injury 
to the root is constantly utilized technically in 
the cultivation of trees. In tranplanting seed- 
lings of forest or fruit trees the main root is 
either twisted spirally in the hole where it is to 
be planted or it is shortened about a third. A 
stronger cutting back is not advisable because 
adventitious roots always develop more weakly 
the older the parts of the axis which are 
twisted or cut back. 




Pig-. 3. Branch of a spruce 
root on which a fleshy com- 
pensatory root has been form- 
ed above the dead tip. (After 
Nobbe.) 



b. Special Cases of Disease. 
Retrogression in the Citltivation of the Larch. 

As a striking example of the disadvantages developed by the cultivation 
of plants from mountain climates when grown on the plains, we might con- 
sider the often noticed retrogression in larch plantations. Kirchner^ 
mentions, when describing the life history of this forest tree, that it is a true 
high mountain tree of the European Alpine and Carpathian systems. The 
natural area of its distribution extends from Dauphine through Switzerland, 
past Vorarlberg, the Bavarian and Salzburger Alps to the Moravian-Silician 
depression, and to the Carpathians, up to the hilly country of Southern Po- 
land. The upper limit for the larch is about 2400 m., the lower one in the 
Alps 423 m., in the Sicilian mountains about 357 m. A\'hile it thrives in 
Scotland, Sweden and Norway, it does not grow very well in Middle and 
Northern Germany or in France. When growing together the spruce usually 
forces out the larch except in the highest altitudes. When the spruce grows 
on dry soil it is shorter than the larch. Of all the indigenous conifers the 
larch needs the most light. It exceeds all conifers and most deciduous trees 
in its transpiration. Because it is not sensitive to cold, as shown by its 
natural habitat, it is much more dependent upon the warm.th of the summer 
lo make its best growth. It lives in regions where the summer is constantly 
and uniformly warm, where there is abundant circulation of air and a win- 
ter's rest of at least four months with a short spring and a rapid transition 
from spring to summer. Because its leaves come out extremely early, it 
makes the most of the very short period of growth. 

These statements are based on the observations of numerous specialists 
and may on this account be acknowledged to be thoroughly reliable. We ob- 



1 Lebensgeschichte der Bllitenpflanzen Mitteleuropas. 
Stuttgart, Ulmer 1904. 



Vol. I. Part 2. p. 157. 



82 

lain an insight into its material composition from the works of Weber^. 
He studied sections of the trunk and the needles of the larch picked in 
October in the Bavarian Alps, in the Spessart, from the plains of the valley 
of the Main etc. In spite of the soil differences, the results agreed entirely 
in regard to the influence of elevation. Weber summarizes these as follows : 

The organic substance of the needles increases with noteworthy regu- 
larity with the absolute elevation of the habitat while the content in pure ash 
decreases. The amount of ash becomes absolutely greater if the larch grows 
on the plains or in moderately high mountains so that therefore to produce 
an equal amount of burnable substance, more and more minerals are taken 
up by the plant, as it^ cultivation descends into the plains. The most im- 
portant elements of the ash, potassium and phosphoric acids, shovv^ a regular 
increase in specimens from the plains in contrast to Alpine Larches. In re- 
gard to the calcium content, the larch of the plains indeed excels, yet the, 
constitution of the soil seems to be very determinative here ; magnesia and 
sulphuric acid show an insignificant increase, while ferric oxid and silicic 
acid show a considerable increase. 

It may be perceived from Weber's investigations how very greatly the 
life habits of this high mountain tree and its mineral composition change 
with its descent to the plains and the question now becomes pertinent as to 
whether the anatomical structure is not also changed by the entirely differ- 
ent conditions of Hfe on the plains. Primarily the plains oft'er strong con- 
trasts from the most intense heat of summer to the great cold of winter. To 
this must be added a lengthened spring with the summer-like days which 
sometimes begin in February, always in March, and the subseciuent relapses 
to cold weather. However, the autumns of the plains may be of decisive sig- 
nificance when a relatively warm, damp period not infrequently lasts into 
December and does not permit the cessation of vegetation. One needs think 
here only of our oaks and apple trees which often enough retain their 
foliage on the tips of the brandies throughout the whole winter. In apple 
trees, especially in trellis and trained forms, many varieties did not develop 
any terminal bud in autumn but the last leaf simply remains in the winter 
in an unformed stage of development. 

In the larch these long, wet and relatively warm autumns stimulate 
growth so that after the normal summer end of the annual ring, a few layers 
of spring wood are formed, as I have often observed. Therefore in such 
cases on the plains the beginning of an absolute dormant period (which 
Kirchner emphasizes as necessary for the normal development of the larch) 
does not take place and the immediate results will frequently be the loss of 
the normal or usual resistance to frost. The frost woimds make possible the 
entrance for all wound parasites which, in the often dense growth of larches 
on the plains and the moist m.otionless air, find the most favorable environ- 



1 Weber, R., Einflufs des Standorteg auf die Zusammensetzung der Asche von 
Larchen. Allgem. Forst-u. Jagdzeitung 1873, p. 368 nnd in Biedermanns Centralbl. 
f. Agriculturchemie, 1875, p. 336. 



83 

ments for their growth and distribution. For this reason the fungus of the 
so-called larch canker, the Dasyscypha (Pesiza) Willkommii, is so abundant 
in old larch plantations and the trunks of the young copse wood are covered 
with lichens. 

The complaint that the trees in northwest and middle Germany and in 
France, on an average, show no satisfactory growth is explained by these 
conditions of growth on the plains diametrically opposed to the nature of the 
tree. This is also the reason for the reaction which has taken place in the 
usual enthusiasm of foresters for the cultivation of the larch. 

The comprehension of our mistakes in growing the larch and the in- 
tenability of the widespread assumption that it can be grown in any place 
has recently been gathering force in forestry circles. A little paper publish- 
ed by the First Commissioner of Woods and Forests in Hameln^ is 
of the greatest significance. He observed that the larch canker occurs only 
where the tree is grown under hindering conditions or is crowded by its 
neighbors. The point which he makes strongly is "that the sun is the nurse 
of the larch." Com.plete agreement with this discovery has com^e from an 
extensive inquiry on the part of the English Dendrological Society contained 
in Sommerville's reports". From this report canker seems to be in- 
creasing in England on the larch and attacks trees from seven to fifteen 
years old most easily. Dampness in dense growths favors the disease which 
occurs less often on altitudes than in hollows. Many practical foresters 
maintain that the disease is inherited through the seed ; and, while Sommer- 
ville does not share this point of view, he cannot disprove the assumption of 
an hereditary predisposition. Also the assertion that nurseries spread the 
disease may not be repudiated entirely. 

We completely understand such statements also heard frequently in 
Germany. Such predisposition to sickness lies in the changed mode of 
growth which is a result of the removal of the tree fr-.m. mountains to 
plains, thus destroying its natural immunity. It is reasonable that nurseries 
with their rapid forcing of the seedlings in manured soils, excusable because 
of agricuhural reasons, increase this weakening of the larch. We find simi- 
lar conditions also for other conifers ; for example, we have examined pine 
seedlings from nurseries and forestry seed-beds which had begun to suffer 
from leaf cast, and we have always been able to prove that the beginning^of 
resinosis was present even in the first annual ring. 

Weber^ observed in beech foliage conditions similar to the larch 
in regard to the difference in the ash content. From investigations from 
eleven different habitats it was found that the percentage of ash in beech 



1 Die Larche, ihr leichter und sicherer Anbau in Mittel-und Norddeutschland 
durch die erfolgreiche Bekampfung des Larchenkrebses. Leipzig 1S99. 

2 Report by Dr. Sommerville on the inquiry conducted by the Society into the 
disease of the larch. Transact, of the English Arboricultural Society. Vol. Ill, 
Part IV. 1893-94. 

3 Weber, Einflufs des Standorts auf den Aschengehalt des Buchenlaubes. AUg. 
Forst.-u. Jagdzeitung, 1875, p. 221, cit. in Beidermann's Centralbl. f. Agrikultur- 
chemie, 1875, II, p. 325. The percentage of ash content and especially of calcium 
and silicic acid becomes greater the more slowly the plants grow. 



84 

foliage from altitudes over looo m. above sea level was noticeably less than 
in that from lower levels. The latter showed, however, in its ash, a smaller 
amount of potassium, phosphoric acid and sulphuric acid, while the leaves 
collected in altitudes were proved to be as rich in these substances as the 
young foliage. The distribution of calcium and silicic acid v/as the opposite. 
The size and weight of the average leaves decrease with the elevation. In 
regard to morphological changes, H. Hoffman^ states that the young sprouts 
of Salix herbacea and 6". reticulata transplanted from high moimtains to low 
levels grow erect instead of lying flat on the soil. When moved from low- 
lands to high mountains, Solidago l^irga aurea becomes an aenemic dwarf. 
Plantaga alpina is a meagre mountain form of PI. maritima not coming true 
to seed and with short ears. The length of the ears increased in the second 
generation on the lowland from 15 to 18 mm. ; the leaves became broader and 
even serated ; there were fewer blossoms at this altitude but not smaller. 
Hieraciun alpinum developed on the lowland isolated sDecimens with tall, 
much branched stems. Aster alpinus in isolated examples developed broad- 
er leaves. Gnaphalium Leant op odium, the Edelweiss, loses on the plains its 
little inflorescences and pubescence. 

The facts ascertained when the larch was brought from the mountains 
to the plains seem to be a very sharp warning to consider more carefully the 
natural requirements of the trees and not to believe, because possibly sup- 
ported by soil analysis, that each tree must thrive where nutritive substances 
are abundantly present for it. The great physical conditions, such as venti- 
lation, illumination and dampness, are determinative factors which, taken 
under due consideration, preserve the natural immunity of the tree and 
make superfluous a petty local combatting of the parasites. 

Lack of Success with Tropical Plantations. 

Like every nation at the beginning of its colonizing period, we must 
recognize that great loses occur in newly organized tropical plantations. An 
essential factor for the protection from agricultural injury is to be found. 
we believe, in the insignificant consideration of the native conditions of 
growth from which the tropical useful plants originate. In regard to the 
transplanting of plants from the plains into an altitude, the increase in the 
relative dampness is of especial importance, next to the decrease in temper- 
ature. These conditions, for example, quickly place a limit for the culti- 
vation of grain. According to Fesca's reports (1. c. p. 42) grain species do 
not flourish at all in the lower regions of the tropics and the ripening of the 
grain becomes uncertain in the higher regions. In Java and Ceylon, culti- 
vation of our species of grains and Leguminoseae with a view to raising 
seeds becomes doubtful, even at elevations of scarcely 2000 m. 

On the other hand a smaller difference between the temperatures of win- 
ter and summer is of great value, especially to tropical plants. Many plants 



1 Riickblick auf meine Variationsversuche, Bot. Z. 1881, p. 431. 



85 

for which the plains are too warm, thrive better in the more uniform cli- 
mate of the higher altitudes. Thus Fesca^ mentions that cocoa thrives 
best at an elevation of about 500 m., Arabian Coffee from 600 to 1200 m., 
and more, and tea from 1000 to 2000 m. For sugar cane, however, places 
are necessary in which occur periods of high temperature. Accordingly 
the cultivation of sugar cane on the sub-tropical plains often reaches even 
to the 35 parallel of latitude, in Mediterranean regions to the 36 parallel of 
latitude where the heat temperature for two to three summer months rises 
above 25°C. The cultivation of sugar cane for factories, however, even in 
narrow tropical zones is seldom successful higher than 300 m. Indeed it is 
planted higher up but then only used for the purposes of propagation be- 
cause of the rapid decrease in the sugar content. At such heights, however, 
the cane escapes the "serch disease" so much feared at present and on this 
account it has been proposed that the plantations for the sugar be regene- 
rated by making propagating fields with the proper cultural varieties at high 
elevations and using as stock the material from these for cultivation on the 
plains. 

In other tropical plants the uniformity of the climate is not the decisive 
factor but the high summer temperatures necessary for the maturing of the 
fruit. Thus in the narrower tropical zone cocoa palms are found at an alti- 
tude of 1000 m. but fruit is rarely produced at an elevation of 900 m. In 
the same way Fesca cites the grape fruit which endures cooler winter tem- 
peratures but requires a high summer temperature to mature its fruit. On 
this account its fruit will ripen in Japan between 31 and 32 degrees latitude 
with an annual mean temperature of i6.5°C. while in Bandoeng on Java at an 
elevation of 714 m. and an annual temperature of 22.7°C. no fruit ripens. 
In Japan during the months of July and August the temperature is high 
enough to ripen the fruit when the monthly mean temperature exceeds 26°C. 
and even in September is more than 24°C. Such temperatures, however, 
are not found in Bandoeng. 

Tea is cultivated advantageously in mountain environments. The tea 
plant loves abundant moisture, hence is naturally a sub-tropical plant. Tak- 
ing advantage of the climate of high elevations, it can be grown successfully 
in the tropics. Thus it is found on Java and Ceylon and in India up to an ele- 
vation of 2000 m. ; the highest plantations in the Himalayas often lie at 
about 2200 m. Tea from the higher locaUties is in fact more highly prized. 
To be sure, greater quantities of leaves are harvested on tropical plains but 
the quality of the leaves is poorer. 

It is a mistake to attempt the cultivation of coffee on plains without 
other shade. Coffee is a tropical plant from high elevations demanding uni- 
formity of climate. The failure of the crops on the plains may often be 
traced to the great fluctuations in temperature and moisture much more 
noticeable there the less the care taken for shading. In the sub-tropical zone 



1 Der Pflanzenbau in den Tropin und Subtropen von Prof. Dr. Fesca. Vol. I., 
Berlin, Slifserott, 1904., p. 41. 



86 

the summer temperature rises so high and the winter temperature falls so 
low that growth, which normally should be continued uninterruptedly, ceases 
for the time being. 

Cocoa, however, to a more marked degree, requires a uniform high 
amount of moisture in the air and soil together with shade and protection 
from the wand ; — it can scarcely ever become too warm for cocoa. Where 
it is cultivated, i. e. the narrower tropical zone up to an altitude of 500 m., 
it developes numerous forms but in all ecological varieties, the same re- 
quirements are felt as to the climate. Fesca (I.e. p. 240) recommends the 
consideration of its need of shade especially when the plantations are young. 
Zehntner^ describes a disease affecting these plantations. It appears 
in the form of brown specks on the bark of two or three year-old sap- 
plings. After transplantation, the little trunks are more exposed to the 
wdnd and the sun and the bark cracks open in different places. 

2. SLOPE OF THE SURFACE OF THE SOH.. 

The slope of the surface becomes a factor which must be considered 
when the local changes due to the influence of the geographical pos-ition are 
studied. Inclinations of from 1° to 10° and at the most 15° are the most im- 
portant, for greater inclinations are less suitable for fields. NolF has 
reported an advantageous result of the inclination of the soil. His ex- 
periments showed that, on rolling land artificially made, an increase of the 
cultural surface is obtained which in growing lettuce increases the yield 
about 31 per cent. But even a slight inchnation has disadvantages since 
rainstorms gradually carry off the friable earth leaving the sub-soil behind. 

The point of the compass toward which the cultural land slopes is also 
very important. Southerly or southeastern slopes are most subject to dis- 
aster because of the great weather changes. The higher temperature pre- 
vailing here forces the growth rapidly in spring ; in summer the danger of 
drying is greater, for the soil is exposed not only to the south winds but also 
to the dry east and southeast winds and anyway to the cool, damp west 
winds, but is protected from the north wind. Since, however, dry winds 
prevail during the spring, i. e. the important vegetative period, the 
southern declivities dry out very especially and consequently in mountains 
the southern side is replanted with great difficulty, hence is usually bare. 

The advantages of the southern exposure are most marked in short 
cool summers. Because of this declivity short lived plants will often ma- 
ture their fruit only in such positions ; hence these slopes are best used 
for the cultivation of such plants as are grown on account of their fruits 
and needing the increased action of warmth and light. A colder exposure, 
however, would be used to better advantage for such plants as are utilized 
for foliage and wood. 



1 Proefstation voor Cacao te Salatiga. Bull. 4. 

2 Noll, Vergleichende Kulturversuche. Clt. Bot. Jahresb. 1900. II, p. 304. 



87 

When cultivating monocarpic plants, such as vegetables, the injury due 
to an otherwise suitable exposure, viz., injury from spring frosts, is felt 
only when the small plants are put out early in spring. There is still greater 
injury to sensitive polycarpic plants to which our nut trees belong. Here, 
wuth a favorable, warm exposure, there is a failure of the harvest, while in 
the same year nuts are produced abundantly with raw exposures. In the 
first case the young shoots and blossom buds, forced out earlier by the great- 
er warmth, are blasted by the night frosts which have not harmed the less 
developed specimens found in high raw exposures. 

In garden plantations, when taking advantage of such positions, one 
attempts to avoid the disadvantages of the spring frosts by holding the 
plants back artificially. This is done by leaving them covered longer, either 
by heaping snow on them or by increasing the mats and litter. With fruit 
trees snow, ice and mulching are heaped about the base in order to keep the 
soil cool as long as possible and thus retard the root activity. 

The cold northern exposure is best for meadows and forests. Eastern 
slopes are unsuitable if the soil is sandy because they dry out more quickly. 
They are therefore more valuable if the soil is heavy. The reverse is true 
of the damp westerly side. HolznerS comparing a slope at 50° north 
latitude, inclined about 10° southerly, with another with a 10° northerly in- 
clination, also took into account the difference in warmth which can be 
called forth by an inclination of IO^ when all other condtions are assumed 
to be equal. The sum total of the sun's rays falUng upon this soil bears the 
proportion on the south and the north slopes of approximately three to two. 
WoUny's- experiments on the warming of field lands deserve 
especial mention. In this work Kerner's' observations are cited, show- 
ing how differently the several sides of a hill warm up. These obser- 
vations follow closely upon the preceding ones. The mean found by 
three years of observation showed that the exposures may be arranged as 
follows, decreasing according to their warmth. The warmest exposure was 
S. W. then followed S., S.E., W., E., N.E., N.W. and N. This scale shows 
that in reality the different exposures do not act as one would first suppose 
theoretically. It would seem first of all that with the sun equally high above 
the meridian the heating would be equally strong and that, therefore, the 
southeast side would receive the same amount of warmth as the southwest 
side. Kerner explains that this is not actually the case by stating that in the 
afternoon the sun at the same height acts more powerfully because the satu- 
ration of the air with water moisture is lower then than in the morning hours 
on which account the absorption of the sun's rays is less in the afternoon. 
Lornez* gives still another reason. On the southwest side, the dew 



1 Holzner, Die Beobachtungen iiber die Schtitte der Kiefer oder Fohre und die 
Winterfarbung immergruner Gewachse. Freising 1877. ^ ^. tt, r^^.^,.,„cr 

-' Wollny, Untersuchungen iiber den Einflufs der Exposition auf die Erwarmung 
des Bodens. Forschungen auf dem Gebiete der Agrikulturphysilc. Vol. I, p. ^bS 

3 Kerner, Ueber Wanderungen des Maximums der Bodentemperatur. Zeitschr. 
d. osterr Ges. f. Metoorologie. Vol. VI, No. 5, pp. 65 fC. 

4 Lorenz und Rothe, Lehrbuch der Klimatologie. Wien 1874, p. 306. 



and moisture from the rain have dried up more than on the south and south- 
cast; it has previously been warmed to some extent and the same amount of 
warmth falhng on a drier soil correspondingly warms it up more. 

The monthly mean temperature, however, and in any case the maxi- 
mum warmth in the different seasons, is more important for plants than is 
the annual average. In this connection Kerner's thermometer observations 
show that only in winter (from November to April) is the maximum soil tem- 
perature found on the southzvest side and that conversely, from May until 
August, the southeast side shows the greatest zvarmth; in September and 
October the south side is ike warmest. This shifting of the maximum may 
undoubtedly be explained by the dry east and southeast winds of midsum- 
mer which, a similar physical composition of the soil being assumed, dry 
the soil more quickly and thereby make it more capable of being warmed up. 

While Kerner's investigations were made on a natural hill, consisting of 
alluvial sand and provided v/ith pretty steep, grass slopes near Innsbruck, 
Wollny experimented with an artificial hill made of sifted calcareous sandy 
Immus whose surface formed an angle of 15°. Here, therefore, the con- 
ditions were adapted to a land which could be used agriculturally. 

Wollny's observations confirm first of all those of Kerner, that the max- 
imum of warmth shifts from southeast in summer to southwest in winter. 
Further, in general, the southern slopes (S.W., S., S.E.) are exposed to great- 
er fluctuations in temperature dian the northerly slopes which respond to the 
smallest fluctuations. In another series of experiments ascertaining the 
temperature of the slopes of beds set at different angles to the compass, com- 
pared during the w^armer season with the temperature on a level field sur- 
face depressed 15 cm., gave the foUov/ing results. The south side is the 
warmest, then follows, as the medium, the \&vq\ worked surface ; then in the 
third place the east and west sides, while the northern exposure of the bed 
seems to be the coldest. If now the bed is placed east and west, one long 
surface lying to the south, the other to the north, these two surfaces show 
the greatest difference in temperature when vegetation can still be found. 
Therefore, if the field is to be laid out in plots, it is better to have them run 
north and south. Cuhivation on level surfaces with a lower temperature 
than on the slope inclined to the south but exceeding that of other exposures 
is the most advantageous on account of the even, and, on an aA^erage, higher 
warming of the soil. 

Later experimentsS however, show the advantages of a position 
inclined to the south, but these are only evident when the moisture is suffici- 
ent and constant. In dry weather or irregular precipitation the harvest is 
smaller. Indeed, in extremely dry weather, the greatest yield is from the 
northerly side, which otherwise gives the smallest. In fact the yield becomes 
less as the angle of inclination increases. Then follow the west and east ex- 
posures. The smallest yield was usually on the south side. 

1 Wollny, E., Untersuchumgen iiber die physikal. Eigenschaften des Bodens auf 
das Produktionsvermogen der Nutzgewilchse. Forsch Geb. d. Agrikluturphysik XX, 
Part 3, 1899, p. 291. 



89 

Naturally other conditions also enter into the question ; thus, for ex- 
ample, color also becomes a considerable quantity when the soil is sufficiently 
damp and has a favorable mechanical form. The darker the earth the more 
plant growth is favored. Mixed soils give better results than clear peat, 
sand or loamy soils. 

a. Too Steep Slopes. 

Soil surfaces of more than 15° to 20° inclination in a small area must be 
used so far as possible for meadow and grazing land if gardening and vine- 
}'ards do not warrant expensive terracing. If the inclination of any surface 
approximates 45° it is urgently advisable to retain all existing vegetation and 
to attempt forestration or to complete it with suitable planting. 

This utilization of surfaces, at such an inclination, is not only the best 
method but also the best protection of the lower adjacent cultivated land. 
Such steep slopes, only found in mountains, rarely have a deep loam even 
when covered with forests. Under such conditions only the thickly matted 
root systems of the trees can keep oft' the destructive gullying and washings 
after heavy rains and from storms after continued drought if the soil con- 
tains much sand. The moss cushions of forests retain moisture necessary 
for the further disintegration of the rocks and increase the tendency to 
form springs; which benefit is felt only on the plains. It is easy to 
observe, that the pith has become eccentric when the trees are growing on 
steep declivities. Mer\ studying firs and spruces of the Vosges, ob- 
served that, in trees growing on steep chffs, the annual rings are more strong- 
ly developed on the side toward the upper incline than on that toward the 
declivity. This occurs especially at the base of the trunk. On cliffs lying 
toward the north and east, the firs and spruces were not only taller and 
stronger but the annual rings of the individual trees varied more markedly 
in the same points of the compass. If the trees have to grow twisted, the 
annual rings show a stronger development on the convex side at the points 
of twisting. 

Unfortunately our cultivated lands show the sad results of the deforesta- 
tion of steep slopes. The forest was here the product of consecutive pro- 
cesses many hundred years old, which probably began with the colonization 
of lichen encrustations on the naked rock. Through the retention of the 
products of weathering, these and gradually larger plants began to form a 
surface soil and with their decomposed bodies furnished the first humus 
substances, making the soil better and better adapted for the growth of 
higher plants. Once robbed of this covering of vegetation, the bursts of rain 
sweep the surface soil downward, exposing the stony sub-soil on the heights 
and filling up the tilled land on the plains. With greater deforestation of 
the mountain, the water supply of the mountain streams becomes the more 
irregular and, with more frecjuent spring floods in the lowlands, covers them 
with sand; also in dry sum.mers the streams are without water. 



1 Mer, Des causes qui produisent I'excentricite de la moelle dans les Sapins. 
Compt. Rend. Vol. CVI, 1888, p. 313. 



90 

Aside from the direct injury of the stones carried down v/ith the mass- 
es of earth, the chief destruction Hes essentially in the covering of the parts 
of the plants which hitherto had been exposed to the free air. Many plants, 
however, die if they are permanently planted too deep and only those can 
withstand being covered with soil which possess the abilit}^ of readily strik- 
ing adventitious roots. Among herbacous plants the grasses growing on 
dunes should be emphasized especially as having this quality (Arundo 
arenaria L., Elymus arenarius L., etc.) ; our cjuack grass (Agropyrum re pens 
P. B.) also easily works its way out through a heavy covering. Among 
trees, the willows and poplars withstand such a covering without great dis- 
advantage, and especially the (Seekreuzdorn) (Hippophae rhamnoides L.), 
which grows on gravel and sand, is found on the coasts of Germany, France 
and England, and serves, with its flat lying roots, as a means of retaining 
the dunes. In opposition to this, the bases of the trunks of many trees, as 
for example, fruit trees, are very sensitive to deep, heavy soil covering. 
Also in transplanting trees, or in grading, a change in level covers the base 
of the trunk, which has been exposed to the air, leads to a weakening and 
shows phenomena of disease which will be treated of more in detail. In 
potted plants the Ericas are most sensitive to the smothering of too deep 
planting. It must be assumed that the cause of death is a lack of oxygen 
for the roots which have been set too deep and covered by large amounts of 
earth. 

Landslides, besides covering the lower lands, expose the roots ; 
which fact deserves attention. So long as the forest remains intact, 
interwoven roots form a network with such small meshes that the soil is 
held firm. If, however, holes are torn in this by the hand of m.an or by 
storms, so that the plants are uprooted, then the soil begins to push down 
from the higher places and in fact the more quickly, as the soil is more 
broken and the wind finds the more access to the torn places. Aside from 
processes of this kind which take place unceasingly in high mountains and 
before which we usually stand powerless, changes in the forests, even on 
the plains, take place constantly as a result of the exposure of the roots from 
the working away of the soil. This is especially the case in forests in hilly 
places when streets are cut through. The forest soil is usually porous or 
becomes so by drying and as soon as the street cuts through a hill over- 
grown with large trees, the free roots are found at the edge of the cut, from 
between which the soil has fallen out or been worked away. The injury is 
two-fold since the exposed side of the root crown weakens the anchorage of 
the trees and the decreased supply of water impairs the formation of the 
tree top. 

The statement that the injury caused by such cutting of the forest for 
shortening the road is compensated for by the increased growth of trees is 
an error. To be sure this may, under certain circumstances, effect a con- 
siderable increment of growth, as, for example, Hartig's^ investigations 

1 Hartig, Ueber den Lichtstandszuwachs der Kiefer. Allg. Forst- u. Jagdzei- 
tung. LXIV, 1888, Januar. 



show. He found in pines 147 years old which had been standing free for 
seventeen years, that the growth had been doubled in the first ten years, 
especially in the lower part of the trunk, where the amount of wood, that is 
the dry weight, had also increased. But he also demonstrated that the in- 
crease fell to the earlier amount, when the food in the soil was taken 
up by spruces which were set out there. In trees whose roots are exposed 
on one side, there is a less water content of the soil wlvich also retards the 
absorption of foods and the influence of light is scarcely able to cause an 
increase of growth. But even if a considerable increase of growth is ob- 
tained by the sudden thrusting of the trees into the light, no agricultural ad- 
\antage is constantly connected with it. In the first place, the branching is 
increased and, in the second, the wood due to the rapidly increased growth 
is coarse grained. This is deduced from the observations of Cieslar and 
Janka^ who investigated the spruce wood produced by long-standing 
cultivation. Produced in great quantity the wood was of strikingly low 
specific gravity because the autumn wood made a scanty growth and the 
tracheids, in the main part of the annual ring, were unusually wide. On 
the other hand, the danger of drying of the top, or blight of the tip, often 
becomes greater. This applies also to deciduous trees grown in dense plan- 
tations. The crowns are suddenly freed, their leaves, in structure and func- 
tion, are adapted to a moderate amount of illumination, can not endure 
the increased transpiration and the excess of Hght so that the tips of the 
branches partially die back. Therefore it is urgently advised in the interest 
of retaining old tracts of woods, specially in sandy soil, to avoid cutting 
through the hills to lay out roads, preferably to lay the road out around the 
hill. According to Hartig- the shock of the sudden opening may also 
lead to injury if, with the increased supply of light, the top is stimulated 
to too active growth. This continues some years, while the available quanti- 
ty of nutriment in the soil lasts. Because the leaf material is increased as a 
result of the intensity of the light, much larger amounts of mineral stuffs 
naturally are required than with growth in dense tracts. Hov/ever, when 
parts of forests are exposed, soluble mineral food material can not be pro- 
vided in sufficient quantity by the influence of the atmosphere, consequently 
after a good growing period there is a decrease in growth due to the "im- 
poverishment of the soil." Following a scarcity of material, however, no 
matter whether due to an actual lack of the substance or to its insufficient 
absorption on the part of the tree, as a result of injuries to the roots or a 
lack of water, there is not only a decrease of growth but also the constitution 
of the wood is weakened. As when growth is forced, only the thin-walled 
spring wood, the vascular tissue, is formed and but little or no strengthening 
tissue, which is present in late wood. 



1 Cieslar, A. und Janka, G., Studien liber die Qualitat rasch erwachsenen Fich- 
tenholzes. Centralbl. f. d. gesamte Forstwesen 1902. Pai't 8. 

2 Hartig, R., Ueber den Einflufs der Kronengrofse und der Nahrstoffzufuhr aus 
dem Boden auf die Grofse und Form des Zuwachses etc. Forstl. naturw. Zeitschrift 
VII, 1898, p. 78. 



92 

b. Growth of Stilts. 

(Elevation of the Roots of Trees.) 

In this connection it is advisable to consider still more closely the fact 
that large forest trees grow with their older root branches above the ground, 
so that the base of the stem is carried on a number of stilts. This position 
gives scantier anchorage to the trees and results disadvantageously since 
they are more easily blown down in wind storms. In addition to this there 
is a smaller provision of water and the roots are peculiarly sensitive. 

These stilted growths form two types ; first, in spruces, where the base 
of the trunk is raised high above the soil and the strong branches of the 
root crown have never been below the top of the earth ; second, in pines, not 
rare on strongly undulating sandy soil, in which the base of the trunk has 
previously been covered with soil or may even frequently rest on its surface 
so that part of the crown is covered with earth, while the other part 
has been uncovered by the washing away of the soil. In extreme cases 
the soil slides out from under the trunk so that the whole tree stands on 
stilts. 

Examples of the first type are described and illustrated by L. Klein^ 
(Figure 4). He explains the production of the phenomenon as follows: — 
If spruces or firs have been felled in the mountains a stump is left 
standing which weathers gradually on its upper surface and becomes 
covered with moss. Later Vaccinia etc. infest this moss cushion beneath 
which is produced a thin humus layer. If self-sown spruces or firs begin to 
grow on the moss-covered surface of the stump, the little young growing 
roots creep under the moss-covering in all directions over the surface of the 
stump and then down its sides to the soil, and develop further there, like every 
other root. In the course of many decades the roots become stronger, the old 
stump slow'ly rots away. Klein answers the question, as to wh}^ one usually 
fi.nds spruces much more rarely than firs and never any deciduous trees with 
this stilt-like growth, when he states that the water needed by deciduous 
trees is possibly ten times as great as that of conifers and that on this ac- 
count the seedling of a deciduous tree would not find enough water perma- 
nently on the surface of the stump for its development. Even if deciduous 
trees do not grow on stilts, yet similar structures such as the sheath growth, 
may nevertheless be found. This occurs especially in willows. Where old 
willows grow along country roads, one finds at times the appearance of a 
new trunk growing independently out of the decayed heart of the hollow 
old trunk, so that the woody cylinder of the old trunk surrounds the young 
tree like a wide sheath. Such cases are easily explained in the pollarded 
willows when the crown is entirely cut off every year or every second year, in 
order to obtain as many young shoots as possible. With the rapid rotting of 
willow-wood on large pollarded surfaces, soil accumulates very quickly from 



1 Klein, L., Die botanischen Naturdenl<maler des Grofsherzogtums Baden u. ihre 
Erhaltung. Festrede. Karlsruhe 1904, p. 13, Fig. 7. 



93 

the dust blown from the street into the depressions of the wounded surface, 
in which seeds of all kinds of weeds find instant lodgment. Now if a wil- 
low-seed falls into one of these accumulations of soil, the young seedling 
finds space for development and its roots finally reach the soil through the 
rotted wood of the old trunk. When an adventitious root of especial length 
grows downward from the pollarded surface at the crov-n-i of the tree, with- 
in the hollow trunk, it has the appearance of a young trunk. 




Fig. 4. stilted spruce near Schc>^nunzach in Stiibewasen. (After L. Klein.) 
A case, due probably to the same conditions, which cause the stilt-like 
growth of spruces, was shown as recently as the 8o's of the last century in 
Kohlhasenbruck near Neubabelsberg (District of Potsdam). The stump 
of an old oak, about 75 cm. high on the village street, had formed a broad 
hollow cylinder by the rotting of all of the heart wood. This was half filled 
with rotten wood and earth and a healthy oak, possibly thirty years old, 
stood in this as in a sheath. 

In spruce plantations one finds at times the so-called "Harp-trees" m 
which a number of side branches have becomp elevated at right angles to the 



94 

main trunk which the wind has blown down, part of whose roots, however, 
still remain in the soil, and therefore are still living. Adventitious roots 
serve the needs of these growths for nutrition. The spruce is certainly the 
one of all the conifers which can most easily overcome all injuries by develop- 
ing adventitious organs. 

It also withstands pruning very well and can therefore be used ad- 
vantageously for hedges, only the hedges must be thinned constantly, or 
they become bare underneath. The ability to form new tips when the old 
ones have been removed, a characteristic of spruce and Araucaria, is taken 
advantage of in horticulture, in propagating by cuttings. 

On the other hand, the regeneration phenomena of tlie older pine are 
most stable and fixed. The second type of stilt-growth occurs especially 
with this tree, if, in a hilly place, the porous sandy soil slides downwards 
from the effects of grading. In the struggle for existence, however, the 
pine when grown from seed can withstand much better exposure of its roots 
than spruces and firs ; this is because the roots habitually grow perpendicu- 
larly into the ground. In the two illustrations which reproduce two examples 
of Pinus silvestris from the Grunewald (back of Paulsborn) near Berlin, this 
perpendicular downward growth is shown especially well in the side roots. 

Figure 5 shows two pines standing back of one another with the bases 
of their trunks about i meter above the ground. The strong main roots send 
their side branches (arising directly on the underside) into the ground in 
parallel and perpendicular directions, indicating that the pine roots deeply. 
The front tree is possibly 60 years old ; the specimen behind it is younger. 
Figure 6 is taken from another side and shows the side roots starting at 
right angles from the main branches which spread horizontally from the 
root crowns. However, in the middle of the stilt appearance, may be dis- 
tinctly recognized the original main root which as a prop has grown directly 
into the earth and which endures the chief strain of anchoring the tree in 
the sandy soil. The tree is still well covered with needles. 

One more important phenomenon must be mentioned in connection with 
this form of stilt-growth, viz., many woody tubers with a dense covering of 
bark grow in rows on the upper sides of the strong roots. These in figure 7, 
reproduced natural size, form hemispherical, wart-like prominences up 
to 1.5 cm. high, with a crater-like depressed centre. They correspond with 
the rest of the root in color and bark. 

It is supposed that this arises from an adventitious sprout formation 
in which the young shoots have died immediately and a heavy scar has been 
formed. The fact that these growths come only on the upper side lends 
strength to this supposition. It is well known that when there is this ten- 
dency toward adventitious growths in trees, the formation of such buds of 
all sizes occurs most strongly on the side toward the light (Tiha, Acer). 
This supposition has not been generally confirmed, as the cross-section (Fig. 
8) shows. This illustrates a seven years' overgrowth of a centre of disease 
formed by a homogeneous mas^ of resin. This resin gall, produced by resin- 



95 




Fig-. 5. Stilted piue from Grunewald near Berlin. (Uriy.) 




Fig. 6. Stilted pine from Grunewald near Berlin. (Orig-) 



96 



osis of the wood, ruptured on the outside and was overgrown in the follow 
ing years. The edges of the over- 
growth, still connected in the first few 
years, have grown back farther and 
farther; — in this way, a crater-like 
opening was produced at the top of the 
woody tuber. The new annual rings 
turn to resin every year and always in 
the first spring wood, which consists in 
part of parenchymatically formed 
cells. The resin holes (H) are pro- 
duced by the drying up of the resini- 
fied tissues, in part also by exudation 
of the resin. The edges of the over- 
growth are further apart each time so 
that the last ones (U) are widely sep- 
arated. In this, they show a most ir- 
regular construction often changing 
between every two medullary rays in 
the same annual ring. In the drawing 
G is the normal wood in cross-sec- 
tion and M the regular course of 
the tracheids in longitudinal section. 
These are in the same annual ring just 
as in true gnarls. 




Fig. 7. Resin galls with gnarl 
growth on the upper side of the stilt- 
like root of the pine (natural size). 
(Orig.) 



F'or this reason these structures 

must be classed with the resin galls. 

So far as their production is concerned, it must be assumed that the exposed 

root shows small centres of 
injury from extremes of 
weather on its upper side, 
i. e. the one most exposed 
to such extremes. These 
centres of injury have 
caused a resinosis of the 
tissues, or rather, a com- 
plete resinous liquefaction. 
Wq may assume that frost 
has caused the injuries, and 
especially late frosts, since 
these appearances are al- 
ways found in the first 
formed spring wood. The 

production of these resin 
Fig. 8. Cross-section through a resin gall on the ,i i ^^ . ,^ i. 

stilt-like root of the pine. (Orig.) galls shows that the roots 




97 

exposed in the stilt-like growth are very sensitive. Tt this is true, less extreme 
cases will have to be taken into consideration and a further w^arning be 
given ; when possible the root body must be guarded from complete exposure. 
When roots are partially exposed their bark is Hable to be broken on the 
upper side by pedestrians, with the result that much stronger annual rings 
develop on the under side which is protected from such injuries by the earth. 

The cultivation of seedlings of the different species of our common coni- 
fers under the same conditions gives the best demonstration of these root 
systems. Nobbe^ carried his experiments out with the following re- 
sults: — Six months after sowing, the pines had 3135 root fibres with a total 
length of 12 meters, the spruces 253 fibres, all together 2 meters in length and 
the fir, 134 fibres with a total length of i meter. In one year, in fertiUzed 
sandy soil, the tap-roots of the pine seedling penetrated almost one meter 
deep, while the spruce and fir, under absolutely the same experimental con- 
ditions, went down only one third as far. At the same time the young pine 
developed five series of roots, the spruce four and the fir three. In decid- 
uous trees, oaks and beeches, Tharandt's experiments showed that in the 
same way they form even in the first year a widely branched root system with 
tap roots nearly a meter long. 

Spruce and fir with their weaker root apparattis, v/hich almost im- 
mediately spreads out flat, need a moist soil, while the pine can do without 
moisture, in fact, easily suffers from it. In seedling plantations, where fir 
and spruce thrive, the pine ver}^ often shows pathological resin ducts in the 
wood of its young trunk. The deep growth of the pine also explains its so- 
called "contentment" and its heahhy growth in almost sterile sand. Like 
the lupin it understands how to meet its need for water and food from the 
deep layers of the soil but it demands good drainage. 

This natural advantage of a tap root penetrating at once to great depths 
is made use of only where seeds are planted in forests without necessity for 
transplantation. In the controversy in forestry circles as to the best methods 
of planting, in considering the pine, we would always place ourselves on the 
side of those favoring sowing in the permanent place. For the spruce and 
fir, we consider transplanting from the seed bed to be more advantageous. 
In any event the method of seeding is not the only factor in a healthy devel- 
opment, but soil and position are often decisive. We can not consider ad- 
visable the present endeavor to plant pines everywhere, because they give the 
quickest and therefore the best return from the soil. In our own forests 
comparisons of the trees in deep lying or marshy places with those on free, 
dry regions show that in the marshy localities there is an impoverished growth 
and often a premature dropping of the needles, and that in hilly sandy soil, 
with deep lying ground water, the trees develop to their full strength, even 
f;eing well-preserved when their roots are exposed on stihs. Rechinger- 



1 Dobner's Botanik fiir Forstmanner. IV Edition, revised by Fr. Nobbe, Berlin. 
Paul Parey. 1882, p. 130. 

2 Rechinger, Bot. Beobacht. in Schur. cit. Bot. Jahresber. 1902, I, p. 337- 



mentions the occurrence of stilt-roots in marshy forests, in which 
Alnus glutinosa predominates while isolated Quercus pfiuncidaia, Rhamnus 
Frangula and Sali.v cinerea occur. 

A third cause of the stilt-like growth still remains to be mentioned 
which is different in that the trees are positively elevated, while, in the cases 
already mentioned, the base of the trunk remains at the place where the seed 
was sown. White^ describes occurrences of this kind. He thinks that on 
rocky soil, where the roots must grow flat, the trees are gradually forced 
out of the ground by periods of frost and draught to which they are peculiarly 
susceptible. 

c. Too Deep Planting. 

Too Deep Planting of Trees. 

Almost all our trees, in their later life, stand in a position different from 
that of the seed beds in which they develop. For fruit trees must have a sec- 
ond transplanting when young in order to obtain an abundant ramification of 
the root body. Since these trees must be so transplanted great care should be 
taken that they are not planted deeper than they originally stood. Exper- 
ience teaches that trees can indeed be destroyed through a disregard of this 
warning. In fact many practical workers recommend that each tree in its 
new position be oriented exactly as before in regard to the points of the 
compass, since they think that many kinds of bark injuries from heat and 
frost can thus be avoided. 

Otto- has attempted to decide the question whether the branches of 
apple, pear and cherry trees develop differently in the several points of the 
compass. By chemical analysis, he found essential differences in the com- 
position of the differently oriented one year old branches. The water and 
nitrogen content is the smallest on the east side, while the content in dry sub- 
stances is the greatest there ; but the water and nitrogen content is greatest on 
the north side. This would indicate that the branches v/ere not so fully ma- 
tured here as on the other side of the tree. ' 

Kovessi^ considers the cause of a decreased formation of blos- 
soms to be the greater amount of water and the lesser ripening of the wood 
of the branches. The number of blossoms and fruit was certainly proved 
to be dependent on the water supply of the previous year. The tree bears 
better, if the water supply is scant. Anatomically, the differences in the 
maturity of the branches, according to the points of the compass, can scarce- 
ly be determined since the structure of the same annual ring fluctuates too 
greatly within the different internodes of a branch*. 



1 WTiite, Theodore, Mechanical elevation of the roots of trees. The Asa Gray 
Bull. Cit Bot. Jahre.sb. 1897, I, p. 85. 

- Otto, Arbeiten der Chemischen Versuchsstation zu Proskau. Cit. Bot. Cen- 
tralblatt 1900, Vol. 82, Nos. 10-11. 

3 Kovessi, F., LTeber die Beziehuna;- des Wassers zur Reife der Holzpflanzen. 
Biedermann's Centralbl. 1902, p. 161. 

■* Sorauer, Beitrag- zur Kenntnis der Zvveige unserer Obstbalinrie. Forsch. a. d. 
Gebiete d. Agrikulturphysik, Vol. Ill, Part 2. 



99 

Also, we know nothing definite, at least nothing which holds good in 
general, of the anatomical changes taking place when trees are planted too 
deep. In some cases it has been observed that the ducts are filled with 
brown, gum-like stifle masses, in others they are filled with tyloses accom- 
panied by a brown discoloration of the walls. Gummy swellings of the mem- 
branes are not infrecjuent. But these are all only occasional observations 
and experimental study of the question is still needed. 

We will limit ourselves on this account to the enumeration of the dis- 
coveries already made as to the influence of the two factors occurring most 
generally when trees have been planted too deeply — the lack of oxygen and 
the excess of carbon dioxid. We know that plants without a supply of oxy- 
gen gradually die. If the living cell can take up no oxygen, it changes the 
direction of its life-functions. Later it passes over into a state of rigidity, 
since the phenomena of movement cease in the cytoplasm., the sensitiveness 
to stimuli is lost and growth becomes inhibited. The plant, however, 
does not die immediately. It continues to give off carbon dioxid for 
some time and, with a renewal of the oxygen supply, it can even re-assume 
its usual functions after a rather long apparent deatli. In this continuation 
of life without oxygen (anaerobic) the oxygen necessary for the life pro- 
cesses must be furnished from the substance of the plant itself and has been 
called intra-moleciilar respiration. 

Lechartier and Bellamy^ in a series of experiments, have proved 
that alcohol is formed in the parenchyma cells growing without a 
supply of oxygen, not only in our pitted and other fruits, but also in the roots 
and leaves. Stocklasa has also proved most recently tiiat there is a forma- 
tion of lactic acid. Even in fungi (Agaricus campestris) , Muntz- found 
alcohol and hydrogen in considerable quantities if the fungi were kept 
for some time in air free from oxygen. The material for this alcohol can 
have been furnished by the kind of sugar alone present here, named man- 
nose, while in other fungi, producing only alcohol, (without hydrogen) in 
an atmosphere of carbon dioxid, the trehalose must have l.een fermented. 
If the lungus is not kept too long in the oxygen- free air, it can take up again 
its normal life-functions, as has recently been proved by Krasnosselsky'' 
for Miicor spinosa and Aspergillus niger. Adolf Mayer* had earlier 
expressed his opinion that fermentation produced by yeast, is a re- 
sult of respiration in the absence of oxygen. Pasteur'' and Bohm" 
had really proved already that all more highly organized land and water 
plants behave in a very similar way. since, in media free from oxygen, they 

1 De la fermentation des pommes et des poires. Compt rend. t. LXXIX, p. 949. — 
De la fermentation des fruits ib. p. 1006. 

2 Comptes rend. I.XXX I, p. 178. 

s Krasnosselskv, Atmung und Garung der Schimmelpilze etc. Central))!, f. 
Bakteriologie etc., 1904, Vol. XIII. Nos. 22-23. 

4 Mayer, A., Untersuchungen uber die alkoholische Garung. Landwirtsch. Ver- 
suchsstationen, 1871. 

•"' Paits nouveaux pour servir ^ -la connaissance de la theorie des fermentations 
proprement dites. Compt. rend. 1872, p. 784. 

6 Bohm, Ueber die Respiration von Landpflanzcn. Sitzungsber. d- k. Akad. d. 
Wissensch. 67. Section I. 



lOO 

reduce a part of their substance by fermentation to carbon dioxid and alco- 
hol, as do the yeasts in self-fermentation. The green parts of plants at any 
rate, with sufficiently intensive illumination, can establish an atmosphere 
suited to their normal respiration by decomposing the carbon dioxid which 
had been given off immediately before. Aerobic and anaerobic respiration are 
interdependent and anaerobic is able to withstand total destruction for some 
time, even if growth is impossible This retardation becomes greater as the 
temperature is lower. Thus, for example, Pfeffer^ cites the observations of 
Chudiakow, that the failure of the carbon dioxid production, i. e. the pos- 
pibility of living, begins after twelve hours in seedlings of maize at a temper- 
ature of 40°C., after 24 hours at i8°C. and only after some days at a lower 
temperature. If an organism or one of its members always has a lower 
vitality, it also will keep alive longer in a place free from oxygen. Thus, 
under such conditions, apples and pears at a moderate temperature have 
been kept growing and ripening for months while rapidly growing moulds 
and aerobic bacteria went to pieces quickly. In seedlings of phanerogamic 
plants (Vicia Faha. Ricinus etc.) there is an increase in the intra-molecular 
exchange. 

Stich's^ experiments show that single plants at times, or parts of 
plants, at first exert no influence on the oxygen content in the air by their 
respiration since, in a hydrogen atmosphere, they form exactly as much car- 
bon dioxid as in air. With 8 per cent, of oxygen in the air, the respiratory 
cjuotient was still normal, — with a lesser content (2 to 4 per cent.) it was 
changed in favor of carbon dioxid because an intra-molecular respiration 
took place. When the plants were kept for a longer time in an atmosphere 
poor in oxygen, the normal respiratory quotient was gradually produced to- 
gether with a decrease of the absolute amount of oxygen and carbon 
dioxid. In a gradual withdrawal of the oxygen, the intra-molecular 
respiration is first stimulated by a considerably lower percentage of oxygen 
than when the oxygen diminution is sudden. 

Brefeld's^ experiments lead to the conclusion that alcoholic fer- 
mentation in all plants, from the lowest to the highest, takes place as soon 
as the oxygen supply ceases. A very essential difference is shown, however, 
in the different organisms which produce alcohol. While generally in yeast 
(Saccharomycetes) the phenomenon of fermentation is to be considered the 
climax of the normal activity of the organisms (which actually grow during 
the process of sugar decomposition)^ it appears in the cells of phanerogams 
as an abnormal process ending prematurely in the death of the cell. This 
differs essentially from the pure fermentation of yeast producing only alcohol 
and carbon dioxid, by the appearance of further products of decomposition 
among which fusel oil and acids are especially noticeable. There is a great 



1 Pfeffer, Pflanzenphysiologie, 1897. Vol. I, p. 544. 

2 Stich, C, Die Atmunj? der Pflanzen bei verminderter Sauerstoffspannung und 
bei Verletzungen. Flora 1891, p. 1. 

3 lUeber Garung III, Vorkommen und Verbreitung- der Alkoholgarung im Pflan- 
zenreiche. Bot. Zeit. 1876, p. 381. 



101 

difference in the ability of fungi to endure alcohol, as is shown among those 
which still introduce an actual alcohol fermentation. For Saccharomycetes, 12 
per cent, of the weight is the limit of growth ; 14 per cent, the limit of fermen- 
tation. In Mucor racemosus, which lives on sugar without free oxygen, the 
limit of growth and of fermentation lies between 4^4 and 5^ per cent, alco- 
hol ; Mucor stolonifer, on the other hand, no longer grows and can not be- 
gin fermentation with 1.5 per cent, alcohol. It should be concluded from 
these results that imder the same external conditions even phanerogams 
succeed in forming alcohol of very different percentages and endure it in 
different amounts. 

Later Muntz^ speaks very generally of alcohol as one of the decomposi- 
tion products of organic substances formed on the surface of the earth as 
well as in the soil and in the depths of the ocean and distributed in the at- 
mosphere according to the laws of the tension of gases. 

It can not be surprising that organic acids, among others acetic acid, 
occur in the fermentation of alcohol. It is very probable that the accumu- 
lation of such acids must ultimately act as a poison upon the organisms and 
that in roots, which are entirely or almost entirely cut off from atmospheric 
oxygen, there will begin a gradual dying back. 

When trees have been planted too deep and the roots need an abundance 
of air, perhaps more than the top part of the plant, the lack of oxygen will 
be felt more quickly the greater the power of the soil to hold water and the 
more the parts are cut off by water-. Water near the living roots 
becomes more and more a source of danger for the larger, healthy roots 
and for the sunken bases of the trees, since the water becomes more and more 
charged with carbon dioxid. If healthy plants are set in water containing 
much carbon dioxid they begin to wilt and the leaves begin to die back'\ 
Kosaroff's^ studies on the absorption of water in insufficiently drained 
soils, i. e. those poor in oxygen a..d rich in .^arbon dioxid, are especial- 
ly interesting. The water absorption and tianspiration were proved to 
be repressed by the carbon dioxid. Plants whose roots remained in an at- 
mosphere rich in carbon dioxid lost their turgidity immediately and be- 
came limp ; when kept there longer they disintegrated. In experiments in an 
hydrogen atmosphere where, therefore, only the lack of oxygen becomes de- 
pressing, it was shown that this circumstance does not act in any way as in- 
juriously as an excess of carbon dioxid. 

Therefore, in the roots of trees lying too deep, death by poison begins 
by attacking first the tender organs, later the older ramifications of the roots. 
At the same time the putrid products of decomposition make the whole soil 
unfit for the growth of plants. Bohm-^' cites an example in the dying 

1 From Compt. rend. Vol. I.XXXXII, p. 499. cit. in Biedermann's Centralbl. 1881, 
p. 709. 

- Mayer, Agrikulturchemie, 5th Edition, 1901, Vol. I, p. 116. 

3 "Wolf. W., Tageblatt der Naturforscher-Versammlung- zu Leipzig, 1872, p. 209. 

■i Kosaroff, Einfluss verscliiedener ausserer Faktoren auf die Wasseraufnahn\e 
der Pfltinzen. Dissert. Leipzig, 1897, cit. Naturw. Rundschau, 1897, No. 47. 

5 Bohm, J., Ueber die Ursache des Absterbens der Gotterbaume und uber die 
Methode der Neubepllanzung der Ringstrasse in Wein. Faesy & Frick. 



102 

Ailanthus trees of the Ringstrasse in Vienna which had been planted too 
deep. These trees years before had fallen off in growth, for in the first year 
after they were planted, their annual rings were more than 3 cm. broad, in 
the last year the growth was 0.5 cm. At the time of death the earth about 
the roots was found to be so injurious that seeds of different plants sown in 
the soil in the open and under bell jars began to decompose at once. Seeds 
developed luxuriantly, however, after this soil, rei^eatedly washed with 
water, had been exposed in thin layers to the atmosphere for eight warm 
days in July. Similar experiments were undertaken by Mangin^ who, 
before this time, had ascribed the diseased appearance of tlie street trees in 
Paris to the bad composition of the soil. Seeds and tubers sown in soil re- 
moved from around diseased roots showed an interrupted development. 

The air tests made near the diseased roots of Ailanthus showed a de- 
ficiency of oxygen and a preponderance of carbon dioxid and Mangin- 
suspects that the lack of oxygen may be traced back to a reduction by 
sulfids. Certainly numerous micro-organisms co-operate in the decom- 
posing process of the roots. However, such an attack by the suitable 
bacteria would not have taken place if the oxygen in the soil had not begun 
to be deficient. 

When trees with spongy bark have been planted too deep, as in the 
above mentioned Ailanthus trees in Vienna, the bark under the soil is found 
entirely rotted away. According to the age and the liark structure of the 
tree, as well as the physical constitution of the soil, a disturbance of the ab- 
solutely necessary circulation of the air will appear sooner or later in the 
buried base of the trunk. This disturbance will be felt also in both the ven- 
tilatory systems of the trunk, viz., in the vascular system of the wood body 
and the bark system communicating with it by means of small hollow spaces. 
The green bark parenchyma protected by the more or less strongly developed 
cork is bathed by the atmospheric air; it penetrates through the lenticels 
into the intercellular spaces where it circulates. The air penetrates the ducts 
of the wood, partly through the water from the roots, but largely by diffu- 
sion from the sides and is also in circulation, as mentioned above. In fact, 
as may be assumed from the investigations, of O. Hohnel", a daily 
periodicity probably takes place in this circulation. The ducts originally 
filled with water are partly or entirely emptied in the course of the day, 
since the superior and surrounding tissues draw away the water. The trans- 
piring leaf body of the tree needs a very large amount of water and draws 
it from the wood tissues of the branches which make good their losses from 
the trunk, in which therefore a suction wave advances down toward the 
base and thence out into the roots. 



1 Mangin, L., Sur la vegetation dans une Atmosph&re viciee par la respiration. 
C. rend. 1896, p. 747. 

- Mangin, L., Sur I'aeration du sol dans les promenades et plantations de Paris, 
C. rend. 1895, II, p. 1065. 

3 V. Holinel, i?eitrage zur Luft- und Saftlievvegung in der Pflanze. Pringsh. Jahrb. 
f. wissensch. Bot. Vol. XII, Part I, p. 120. 



103 

Since more water is drawn away from the ducts than can be replaced 
instantly, a space partially filled with air appears in these ducts causing a 
negative pressure (suction) which is so much the greater the less the amount 
of air present at the beginning or slowly diffused through the membranes, for 
so much the more must the originally small volume of air be distended to fill 
out the hollow space which is always becoming greater. In the night, when 
the evaporation is arrested or very much repressed, the ducts of the trunk 
again suck up great amounts of water, in fact, this suction is often increased 
by the pressure proceeding from the roots which can press so much water into 
the ducts that a great part passes through the membranes into the surround- 
ing cells and intra-cellular spaces. If this liquid drawn up from the root body 
or pressed up by it is liealthy, a considerable infiltration into the intercellular 
spaces will take place without disadvantage to the body, as has been 
shown by MolP. If, however, the water mass is already laden with the 
products of fermentation from the putrefying root tips, we see that these 
poisonous substances get into the especially sensitive sapwood and bark and 
thus the dying back easily spreads. 

Trees planted too deep, however, usually die only in heavy soil per- 
manently loaded with water. In light soils they suffer but do not die. If the 
heavy soil with its water burden surrounds the base of the trunlc and pre- 
sents intercellular ventilation by means of the lenticels, alcoholic fermenta- 
tion and the formation of acetic acid must naturally appear in the bark cells 
and lead to a dying back which is continued radially to the cambial zone and 
the young sapw^ood which is especially active in conducting water. 

Thus there remains from year to year a cylinder of heartwood in the 
middle of the trunk which is always becoming smaller and smaller and which 
usually has to meet the water need of the aerial part. The heartwood which 
is poor in water, however, is less suited for conducting it and the dead tis- 
sues of the wood, which at any rate can still conduct water mechanically, 
will not be able with their help to meet the need of w^ater in the crown. Con- 
sequently, the tree ultimately wilts or fails to put out buds in spring. 

The fact that the non-parasitic processes of decomposition in the buried 
end of the trunk cease near the upper surface of the soil leads to the theory 
that processes of decomposition are not able to attack healthy plant cells but 
only those weakened and functionally abnormal. Such weakening is actually 
present. It was mentioned at the beginning that cells full of life and rich in 
content, when shut away from the oxygen of the air, begin at once to de- 
velop alcohol through the activity of fermentation (alcoholases) which was 
not present previously and which disappears again if the plant regains its 
atmospheric air. It has been proved further that the plant, in the absence of 
oxygen, continues for some time to eliminate carbon dioxid in considerable 
quantities (respires intra-molecularly) but that these amounts of carbon 



1 Untersuchungen iiber Tropfenausscheidung und Infektion, 18S0, p. 78. Sep. 
aus Verslag en Mededeeling d. Koninkligke Akad. Amsterdama, cit. in Pfeffer, 
Pflanzenphysiologie, 1881, I, p. 159. 



104 

dioxid are still smaller when the experiments are continued longer than 
those of plants respiring in air which contains oxygen\ Since the 
carbohydrates (starch, sugar) furnish the material for respiration, it 
should be assumed from the above facts that these material contents of the 
cell are made use of abnormally in the absence of oxygen. With Pfeffer- 
respiration can be conceived of as a process set up .by two dove- 
tailing processes. The first is the intra-molecular respiration ascertained in 
the phenomena of fermentation which Borodin^ named internal oxidation. 
The second process, possible only with a supply of oxygen from with- 
out, is the immediate further oxidation of the products of fermentation 
in the moment of their production. Jf this last act, absolutely necessary for 
the life of the cell, is suppressed, not only the zone of the trunk of the tree, 
planted too deep and lacking oxygen, loses its respiratory material, that is, 
always becomes poorer in reserve substance, but it also forms those products 
which lead to decomposition and the death of the cell. Insufficient respir- 
ation therefore is a necessary preliminary condition for the dying back and, 
to the degree in which the buried part approaches the surface of the soil, 
gradually getting more and more oxygen, the ferm^entation will become 
weaker and weaker and pass over into the normal process of oxidation so 
that decomposition gradually reaches its limit. It is thus Only a question 
whether the tree has the possibility of forming new roots in the soil above 
these limits in order to meet the loss of water produced by the transpiration 
of the foliage. The stunted production frec[uently observable in early years 
disappears as the more plastic material can pass downward and be used for 
the new structures in the wood ring of the trunk and the roots. The more 
rapid the growth, the greater the energy of respiration (as shown by Saus- 
sure) and the more the flat new root body is reached by Hght, so much the 
more will the production of carbo-hydrates and its absorption of oxygen 
and production of carbon dioxid increase*. 

The behavior of the trees planted too deep or only partially buried de- 
pends naturally upon their specific character. In willows and poplars, for 
example, the part 'sunk in the earth may indeed be found to be dead, but 
near the top of the soil, the decomposition appears to have been stopped. 
Numerous adventitious roots have been formed from the trunk v«hich, some 
time after the tree has been buried, starts a healthy development of the crown. 
The tree is therefore saved if it is able to produce new roots quickly near 



1 Wortmann (Ueber die Beziehungen der intramolekularen zur normalen At- 
mung der Pflanzen. Inauguraldissertation. Wiirzburg- 1S79) states, to be sure, 
that the amounts of carbon dioxid are equally large in intra-molecular and normal 
respiration; it seems to me, however, that the short duration of his experiments 
also caused the observation of the after effects of a previous normal functioning. 
He, himself, admits (p. 31) that in a longer period with no addition of oxygen a 
smaller amount of carbon dioxid was produced by the plants under experimentation 
than had been the case in the constant presence of oxygen. 

2 Pfeffer, Ueber das Wesen und die Bedeutung der Atmung. Landwirtsch. 
Jahrb. 1878. 

3 Borodin, Sur la respiration des plantes pendant leur germination. 

* Borodin, MSmoires de I'Aead. imperiale des sciences de St- Petersbourg. VII 
s6rie. 1881. 



105 

the earth's surface. It is well-known that Ericaceae and Epacrideae are 
especially sensitive to too deep planting. In these species the base of the 
trunk dies even when the root has not suffered very much. When the sap- 
ling shows moss and lichen growths at the base, there is every reason for 
being careful. 

In nurseries no one general rule holds good in regard to the depth of 
planting. Aside from the important physical composition of the soil much 
depends in grafted trees upon the stock. Fruit varieties grafted on wild 
stock should be so planted that the root neck remains in the plane of the 
surface of the soil or even projects a' little above it. In fact in marshy soil, 
with a great deal of moisture, planting is made in hills. Pears grafted on 
dwarf stock (on quinces) and apples (on Doucin and Paradise apples), on 
the other hand, must be planted at least so deep in the soi! that the place of 
grafting is found at the surface level of the soil; i. e., the whole stock under 
the soil. From this a considerable number of adventitious roots develop 
which are especially useful for nutrition. 

Bouche^ has given a splendid summary of practical experiments. 
He refers first of all to the fact that in old healthy trees the strong 
roots are seen to appear above the soil and that this appearance of the root 
neck is normal. Many trees can survive deep planting when young, since 
they put out new roots from the base of the trunk just below the surface 
(elms and lindens) ; others, on the contrary, are very sensitive, as, for ex- 
ample, pears, maples, oaks, most of the Rosaceae, plane-trees, walnuts, red 
and white beeches. Also most conifers require care in planting, as, for ex- 
ample, the genera Pinus, Picea and Abies and at times also Thuja, especially 
Thuja (Biota) orientalis and related species, while deep planting has been 
proved to have been endured by Thuja occid entails, T. IVarreana, T. plicata. 
Bouche found trunks 5 to 8 cm. thick putting out a number of new roots from 
their buried bases whereby they were very much strengthened. Juniperus 
communis must be planted shallowly but J . Sahina and related species sur- 
vive deep planting with advantage. It has already been stated of poplars 
and willows that deep planting is counterbalanced at once by the formation 
of new roots on the surface of the soil. In weak trunks it is often found 
that the roots formed just below the surface get the upper hand over the 
older, deeper ones. It is actually even more advantageous to plant many 
bushes deeper than they stood before because they strengthen themselves by 
numerous new roots from the buried base of the stems. This is noticeable 
for example in Calycanthus, Cornus alba and C. sibirica, Ribes, many kinds 
of Spiraea, Viburnum Opulus, Aesculus macrostachya, Symphoria, Ligus- 
trum, Rosa gallica etc. On the other hand Caragana, Berberis, Colutea, 
Cornus mascula and C. sanguinea, Corylus, Cytisus, Rhamnus, Sambucus, 
should be planted at the old level. 



1 Bouche, C, Ueber das Tiefplianzen '"on Baumen etc. Monatsschr. d. Ver. z. 
Ford. d. Gartenb., v. Wittmack, 1880, p. 212 and Wredow I.e. p. 75. 



io6 

In planting streets, besides the embankment which sometimes becomes 
necessary, Ihe asphalting and cementing of the street causeways is also very 
injurious to the roots of the trees. The injury is due not only to the shutting 
off of the atmospheric air but also the loss of precipitation from the air, upon 
which trees in large cities become so much more dependent, as the level of 
the ground water has fallen because of canalization and the workings of the 
subsoil in building. Young trees which are planted after the falling of the 
level of the ground water strive to reach this despite the increased depth of 
the springs. Consequently in order to facilitate this, the holes for planting 
the trees must be made considerably deeper in such localities. According to 
Bouche, this increased depth amounts to 60 cm. in Berlin so that now the 
holes for planting trees must be dug i. 5 cm. deep. 

Too Deep Sowing of the Seed. 

The discovery has also often been made that from a plentiful sowing 
of good fresh seed a comparatively small number of plants is produced. As 
is generally believed, the cause lies more frequently in sowing the seeds too 
deep. When harrowed in or hoed under in places, as is customary with 
barley^, some seed grains necessarily come to lie too deep, others 
too superficially. Uniformity can be obtained only by planting with a drill. 
But even the gardener, who can cover his seeds very uniformly in seed pans, 
not infrequently obtains only a low percentage of plants in sowing very fine 
seeds even if the seed was good and of high germinating quality. 

The processes causing the loss, however, are not always the same, and 
do not always take place under the same conditions ; on this account it is 
impossible to generalize. In order to protect oneself from injury in this 
connection, there is nothing to be done except to understand clearly the in- 
fluence of the different factors to be observed in sowing seed and to see' 
which combinations exist in every individual case. 

There are three phases in germination. Each can be disturbed and 
cause failure. The first stage consists of the swelling of the seed and is a 
mechanical process, in which (probably by water condensation) an increase 
in temperature has been observed. This introduces the second stage, the 
mobilisation of the reserve substances, a chain of chemical phenomena, and 
these accompany the third act, that of the formal development. 

Disturbances in the stage of swelling have often been obser\'ed. Nobbe 
and Haenlein- found especially in Papilionaceae and Caesalpiniacea, 
that the seed shell at times is so hard that water can not enter, that the seeds 
retained the embryo for years without development, but always in a healthy 
condition. The seed did not germinate because it did not swell. In clover 
seed, the superficial shell or hard layer containing the coloring matter, is 



1 Eggers-Gorow, Versuche iiber den Nutzen oder Nachteil einer flachen oder 
tiefen Bestellung der Gerstenkorner. Mecklenta, landw, Ann, 1874, No. 23. 

- Nobbe und Haenlein, Ueber die Resistenz von Samen gegen die aufseren 
Faktoren der Keimung. Versuchsstationen 1877, p. 71. 



107 

shown to be so impermeable for zvater that clover seeds can He from one to 
two weeks m Enghsh sulfuric acid, and for years in water, without losing 
the coloring matter which in itself would be soluble in water. In such cases 
only mechanical treatment is of any use. Gaiter and Klose^ mixed 
the seeds of lucerne (alfalfa) and varieties of clover with fine sand and trod 
for ten minutes on the bag containing the mixture. After this treatment, 
13.4 per cent, of the seeds of the lucerne were found to be more capable of 
swelling, 10.2 per cent, of the white clover and 37.8 per cent, of those of the 
bird's-foot, without showing any especial injury. Nobbe cites examples"-' 
of an unexpectedly long retention of the germinating power. 32 per 
cent, of seeds of Piniis silvestris, gathered in 1869, after ha^'ing been kept 
5 years in closed glasses in an occupied room, still germinated, and after 7 
}ears 12 per cent. With red clover seeds (Trifolium pratense), preserved 
in the same way, 10.5 per cent, germinated after 12 years, peas (Pisum sati- 
vum) 4y.y per cent, after 10 years, Spergula arvensis 20 per cent, after 12 
years, flax (Linum iisitarissimum) 49 per cent, after 6 years and 3 per cent, 
after 11 years. Out of 400 seeds of the locust (Rohinia Pseud-Acacia) after 
ten days, longer than which the tim.e for practical purpose does not last, 
71 grains germinated ; at the end of the year, 55 grains ; in the next year 18 ; 
m the following year 7 and, after 7 years, one seed; all were kept contin- 
uously in distilled water which was renewed periodically. From these ob- 
servations it seems credible to us that many buried seeds, unimpaired in life- 
power, survive for very long periods. Even in the locust seeds mentioned 
above, the remainder, left ungerminated after seven years, was still perfectly 
healthy. A slight injury to the seed shell resulted after a few hours in a 
swelling up and also, as a rule, in rapid germination. 

Disturbances of the second phase of the process of germination, the 
stage of chemical action converting the solid reserve substances into the 
easily transpired constructi^'e matter, are observed very frequently. The 
fact that many hard seeds such as Crataegus, Rosa, Juglans, Prunus, lie un- 
harmed for a year in the soil, is not to be confused with real disturbances. 
The difficulty of swelling may partly be to blame here; — during the dry 
time in summer the seeds again become dormant. On the other hand water 
may have permeated them already and have given rise to the formation of 
ferments, which lead to the mobihzation of the reserve substances. But this 
action of the ferment is in itself too slow, up to the beginning of the dry 
summer period, to sufficiently nourish the embryo. In different individuals 
and varieties of all species which germinate with difficulty, germination and 
development is found the spring following autumn planting. This takes 
place especially if the seeds are sown soon after harvest ing and when possi- 
ble with the entire fruit. "Stratification" has been pro^'ed still m.ore effec- 
tive, i. e. the placing of the seed in layers in vessels filled with sand for the 



1 Gaiter und Klose, Quellungsunfahigkeit von Kleesamen. "Wiener landw. 
Zeitschr. 1877, No. 17, cit. Jahresb. f. Agrikulturchemie, XX. Year, 1877, p. 181. 

- Dobner's Botanik fur Forstmanner, 4th Edition, revised by Nobbe, 1882. 
p. 382. 



io8 

winter. The actual disturbances are found to be the lack of external con- 
ditions necessary for germination. Besides moisture and warmth there be- 
long here the unimpeded supply of oxygen and the observance of the time 
when the seed is capable of re-acting. 

The time within which the seed responds to the action of the external 
conditions necessary for germination by a normal transmutation of the re- 
serve substances and the development of the embryo varies greatly, for the 
different families and species, even for individuals of the same variety. It 
is well-known that seeds of willows, poplars and elms must be sown im- 
mediately after harvesting, since they lose their power of germination after 
a few days or weeks, while cucumbers and melons often give stronger, more 
fertile plants, if the seeds have been kept for a year. To be sure, the seeds 
of many of our fruit and forest trees usually germinate after one or more 
years, but the number of the slozv grozving, weakened specimens increases 
with the age of the seed. 

Oxygen should be considered the most important factor next to water, 
necessary for swelling. For germination the seeds never need as much water 
as their substance can take up; the vegetative activity of the seedling begins 
before this time\ If in the beginning there is a scarcity of water 
which can be taken up endosmotically, the seed also takes water up hydro- 
scopically from the atmosphere". Water vapor also condenses on the 
outer surface; in fact, after the manner of all porous bodies, it condenses 
also hydrogen, nitrogen oxygen and other gases. Deherain and Landrin^ 
found that the swollen seeds take up comparatively more oxygen than 
nitrogen from the atmosphere so that more nitrogen remains in the en- 
closed space. After three days the seed begins to give off carbon dioxid and 
this increases so fast that soon more carbon dioxid is present than the oxygen 
enclosed in the volume of the air would warrant, the oxygen has gradually 
disappeared. The excessive production of carbon dioxid is therefore to be 
considered as a product of the processes of oxidation of the inner burning, 
beginning in the seeds. 

These authors pictured to themselves the beginning of the chemical 
actions in the seed in such a way that the rapid condensation of the gas de- 
termined at first for the various seeds will necessarily free the latent warmth 
of the gas and this warmth sufficiently increases the temperature of the en- 
closed oxygen so that oxidation can begin. With this is given the impetus for 
the normal solution of the reserve substance of the seed ; the heat, freed by 
oxidation, favors these processes more and more and they become evident 
externally by the production of carbon dioxid. 



1 Jahresb. f. Agrikulturchemie, 1880, p. 213. 

2 Hoffmann, R., in the Jahresbericht der agrikulturcheniischen Untersuchung- 
station in Bohmen, 1864, p. 6. and Haberlandt, F., in Zeitschrift fiir deutsche Land- 
wirte, 1863, p. 355. Both worlds may be found in abstract in the Jahresb. f. Agrikul- 
turchemie, Jahrg. VII. 1864, pp. 108 and 111. 

3 Compt. rend. 1874, Vol. LXXVIII, p. 1488, cit. in Biedermann's Centralbl. f. 
Agrikulturchemie, 1874, II, p. 185. 



I09 

The preparation for the germination of the dormant seed, according to 
this theory, is the loosening" undergone by the shell of the seed, as the result 
of its swelling with water. The broken cell layers which have become per- 
meable for gases now permit their rapid penetration and their condensation 
therefore gives the first impetus for the process of oxidation which causes the 
transformation of the reserve substances into diffusible forms. Since it can 
be observed with the seed albumen of plants that the breaking down of the 
starch in the seedling begins in the cotyledons in monocotyledons, it can be 
assumed that the part richest in nitrogen, i. e. the embryonic tissue, under 
the influence of oxygen will begin the metabolic reactions and by the develop- 
ment of abundant enzymes act upon its surroundings. 

The disturbance in the second phase of germination can result only 
from a lack of oxygen or also from an excess of carbon dioxid. The state- 
ments of Th. de Saussure confirmed by Deherain and Landrin show that no 
gas is so detrimental to germination as carbon dioxid. Seeds which are kept 
in a mixture of oxygen and hydrogen germinate just as in atmospheric air; 
yet an addition of a few hundredths of carbon dioxid to an atmosphere of 
oxygen is enough to absolutely inhibit germination, when only the little roots 
have appeared. If the amount of carbon dioxid is very considerable seeds 
will not germinate. 

Carbon dioxid in excess is very injurious to other dormant parts of the 
plant. Van Tieghem and Bonnier^ found in bulbs and tubers (Tuli- 
pa, Oxalis c'renata) which respired further in air containing a great deal of 
oxygen, and therefore^ produced carbon dioxid, that they formed alcohol in 
an atmosphere of pure carbon dioxid. Tulip bulbs which had been kept for 
a month in air free from oxygen were suffocated and remained without fur- 
ther development. 

When seed has been sown too deep there is also an excess of carbon 
dioxid and a lack of oxygen. The thick soil covering brings about injuries 
and hinders the germination of the seed but can not, hov/ever, be expressed 
in definite figures. Aside from the different requirements of the different 
species, the optimum thickness of the covering differs for the same species 
according to the com[)osition of the soil, the amount and distribution of pre- 
cipitation etc. On this account the results of the experiments often under- 
taken to ascertain the best depth for sowing differ from one another as soon 
as a definite statement of figures is undertaken. They all agree, however, 
that in doubtful cases it is better to sow with too shallow a covering than too 
deep. 

The purpose of the covering is to hold the young seed firm and to retain 
a sufficient degree of moisture. The shutting out of light comes less under 
consideration. The retention of sufficient moisture for germination must be 
primarily considered. If enough is present, the roots themselves will pene- 
trate at once into the soil even when the seed lies superficially. On this ac- 



1 Bulletin de la societe botanique de France, Vol. XXVII, 1880, p. 83, cit. in 
"Wollny's Forschungen auf dem Gebiete der Agrikulturphysik. 



I 10 

count a perfectly superficial sowing of the seed would be advisable if periods 
did not occur in spring which dry up the surface of the soil to such an ex- 
tent that a temporary or even a permanent inhibition of tlie life activity takes 
place in the seedling. 

The more porous the soil, the greater is the danger of drying out and 
therefore the greater the depth at which the seed must lie. In regions where 
the spring is dry a heavy soil will give a more uniform germination even if 
the sowing is shallow. The same soil and the same depth of sowing become 
dangerous when strong rainfall and great heat alternate rapidly and form 
crusts on the upper surface of the soil cutting off nearly all access of air to 
the seeds then in a most active stage of metabolism. The air enclosed in the 
seeds does not last long. Ventilation of the plant body is, however, absolute- 
ly necessary, even the germinating seed suffers extremely if the air contained 
in it be removed. The formation of heavy crusts on the soil can make the 
depth of sowing of the seed become the cause of considerably injury, which 
in itself would not be injurious. 

How much the lack of air influences the germination capacity of seeds 
is evident from de Vries^ citations. In this connection Haberlandt injected 
curly beet seeds with water under an air pump and observed that the seeds 
took up 71.13 per cent. ; of these seeds thus partially deprived of air only 30 
per cent, germinated as against 90 per cent, of the normal seeds kept as a 
control. In a second experiment all the air was replaced by water forced in 
by the air pump and only 8 per cent, germinated as against 72 per cent, in the 
control. 

Also the time required for germination was shorter in the normal seeds. 
It may well be assumed that the removal especially of oxygen from the seed 
and the hindered diffusion of this gas in new quantities into the intercellular 
spaces is the cause of the loss in germinating power. Dutrochet- 
found even in mature plants that death often occurs if water is injected. In 
the rapid thawing of frozen fleshy parts of plants which, as a result of an 
infiltration of the intercellular spaces with water, have a glassy, translucent 
appearance, the exclusion of the air from the cells by water may contribute 
essentially to their death. 

From the many experiments carried out practically in order to obtain 
j)recise numerical values for the best depth for solving seeds, those of Roes- 
tell, Tietschert, Ekkert and W'ollny are the most thorough. Roestell" 
gives 2 to 4.5 cm. as the most favorable depth for porous, strong, field soil. 

Tietschert* experiments endeavor to determine the maximum boun- 
daries of the most favorable seeding depths in soils differently con- 
structed physically; — 10 cm. was seen to be the rational maximum depth for 



1 De Vries, Keimungssreschichte dor Zuckeirube, Landwirtsch, .Tahrb. v. Thiel 
1879, p. 20. 

2 Dutrochet, Memorires etc. edition Bruxelles p. 211, cit. by de Vries 1. c. 

3 Annalen der Landwirtschaft, Vol. 51, p. 1. 

^ Tietschert, Keimungrsver.suche mit Roggen and Raps. Halle. 1871. 



Ill 

sandy soil, 8 cm. for humus soil and 5 cm. for clay and loamy soil containing 
lime. 

The last two kinds of soil suffer from dry weather so that shallow seed- 
ing gives poor results. The experiments repeated later in the year (August 
to September) gave for all kinds of soil a depth of 2.5 cm. as very unfavor- 
able because of drought ; in this case clay soil was proved most favorable in 
seeding at a depth of 10 cm. It is evident from this that dehnite figures 
must be accepted with great reserve. Ekkert' experimented with rye, 
oats and barley, in loam, in pond slime (silt), in sandy soil and garden 
earth. In seeding rye in separate wooden boxes no difference in the growth 
of the plants was shown between 2 to 8 cm. of covering (as a result of uni- 
form ventilation from all sides). In experiments in the open ground stem 
formation seemed more favored by a lesser depth of the seed, yet this refers 
more to the time of the appearance of the sprout than to its cjuality. Oats 
and barley survive a deeper sowing than does rye. In smnmer a deeper sow- 
ing of the seed is better than in winter. The minim.um covering for grain 
m.ay be 1.5 to 2 cm. ; the maximum favorable for results is 6 cm. 

Later experiments of the same author- bring another important 
factor into consideration which for the same soil acts as a modifier of the 
favorable depth for sowing. The qualiiy of the seed is at times decisive. 
The quality of wheat seed, however, with which the first experiments were 
made did not seem to have any influence on the capacity for germination but 
the development of the young plant with equal depth of sowing was better, 
the better the quality of the seed. With a medium 5 cm. depth of sowing 
(experiments with sandy soil) all qualities gave the longest straw and the 
longest heads. The relation of the weight of the grain yield to that of the 
straw is lower, as the seed is poorer and the sowing deeper. Experiments 
with barley confirmed the results obtained with wheat ; the less the depth of 
sowing and the better the quality used for the same depth the earlier the 
seed sprouted. The sum of the sprouted plants was no less with inferior 
seed but the influence of the depth of sowing was so felt in this quality that 
a shallow sowing gave a much longer straw. In general it must be said that 
Ihe depth of sowing, conditions otherwise being thought equal, will influence 
first of all those developmental stages which are connected with the early 
stage. How^ever, the quality of the grain depends upon the early develop- 
ment in the number of sprouts and the length of the heads as well as the for- 
mation of the young heads and is therefore infiuenced by the depth of the 
sowing. On the other hand the quality of the harvested grain depends upon 
the nutritive and weather conditions of the current year, and will therefore 
be scarcely more influenced by the first development or inherited peculiarity 
of the grain. 



1 Ekkert, Ueber Keimung', Bestockirig- unci Bewuizelung- der Getreidearten etc. 
Inauguraldissertation. Leipzig 1874. 

- Ekkert, Kulturversuch mit Weizen und Gerste verschirdener Qualitat etc. 
Fiihling's Landw. Zeit., 1875, Part 1; 1876, Parts 1 and 2. 



112 



Soaking of the seed, which has often been recommended for Ught soils 
when the time for seeding has been continuously dry, should be used with due 
care. If the weather becomes dry and the water which has been taken up in 
swelling is not enough to make the primary rootlets grow into the soil, then 
there is an unavoidable interruption in growth. This is the explanation of 
WoUny's discovery^ that soaking produces plants maturing later. 

Wollny's- studies on the suitable depth of sowing are most thorough ; 
he determined for grain that sowing 2 to 3 cm. deep furnishes the 




Fi£ 



Rye seedling- with too deep sowing- of the seed grain. Elevation of 
the node of the sprout near the surface of the soil. (Orig.) 



best results in yield. Over and above this a noticeable retrogression is found 
already especially emphasized by Jorgensen^. The last named author 
also found rye to be the most sensitive and wheat the least sensitive. For 
most of the Leguminoseae the depth of the sowing is less important. In con- 
trast to this, varieties of clover and rape have been proved very dependent 



1 Bot. Centralbl., Vol. XXX, No. 15. 1S87, p. 48. 

~ Wollny, Saat und Pflege der landwirtschaftl. Culturpflanzen. Berlin, 1885. 
3 Jorgensen, S., Versuche titaer das Unterbringen der Saat etc. Annalen d. 
Landw. in d. Kgl. Preuss. Staaten. Wochenblatt 1873. No. 11. 



II' 



upon the depth to which the seeds are covered. It seems desirable to have 
this still less than for grain (0.5 to 2.6 cm.). Wollny's experiments showed 
that in dry years a deeper earth covering was more advantageous, in wet 
years, a lighter one. Corresponding to wet and dry weather the time of har- 
\ est was retarded with an increasing depth of sowing, the number of plants, 
which germinated at all and still more, the number which came to harvest, was 
decreased. But it must be emphasized again and again that precise figures 
for the most favorable sowing in the different localities can be collected only 
directly by the local agriculturahst since not only the composition of the 
soil and the weather but also the character of the variety must be con- 
sidered in the matter, as has been shown by Stossner\ 

This same holds good for tubers, bulbs and pieces of roots which are 
used for seeds. In these the soil conditions have an especial weight because 
these fleshy organs which are rich in water are essentially and quickly in- 
fluenced by the soil supply of oxygen . For potatoes, experiments by 
Nobbe- and Kiihn^ have shown that in questionable cases the more 
shallow sowing will be the most advantageous one. In the forcing of bloom- 
ing bulbs excessive losses arise at times from the fact that the bulbs (hya- 
cinths) have been planted too deep in the pot, or when in the pots are cover- 
ed too deep with earth after the rooting has been sufficient. Especially if the 
soil covering is heavy and damp and the bulbs have not matured sufficiently 
the year before on account of wet weather, the "Rotz" (see this in Vol. II.) 
usually appears very easily. 

The oiitomatic regulation of the depth of sowing on the part of dift'erent 
plant races is interesting. In grasses, and in fact, best seen in our grain 
species, the first internode is the part which is destined, when the seed grain 
has been sown too deep, to push the second node which hides the stem eye 
and the side buds, i. e. the node which forms the stem, into the porous, well 
ventilated upper layer of soil. In the adjoining figure 9 we perceive the 
seed grain which is already almost empty and its weakly retained (primary) 
roots which had been formed in the grain. From the seed grain the first 
(over-elongated) internode has pushed the second node nearly up to the 
upper surface of the soil. In this favorable position the secondary roots, 
which exist during the whole life of the plant, have been developed, the eyes 
of the side shoots have attained a further maturity. In shallow sowing both 
nodes lie close to one another and give in cross-section such a picture as is 
shown in figure 10. The nodal tissue seems divided radially by browned vascu- 
lar strands. The vascular-bundle cylinders are those of the primary roots and 
become diseased during or soon after the formation of the secondary roots. 
The ground tissue of the node shows the first circle of vascular bundles (g) 
of the young blade close to the pith shield (m) with its few cells. Branches 
of these bundles, recognizable from their wide ducts (g'), may be seen fur- 



1 Stossner, Unter.suchung-en liber den Einfluss verschiedener Aussaattiefen etc. 
Landwirtsch. Jahrbiicher 1S87. 

2 Nobbe, Handbuch der Samenkunde, 1S76, p. 184. 

3 Kiihn, Berichte aus dem physiolog-. Laborat. Halle, Part I., p. 43. 



."4 

ther out in the axis. 'Phis yoiinij; Made jiosscsscs on the side marked f 
uniformly eonnecti'd l)ark tissue'; on the o])i)()sile side /\ iiowever, the 
first sheath- formed leaf (sell) vvhii-h remains eolorless, and the hud ol the 
next hij^hcr leaf, the lirst j;reen one (hi), which is comi)letely developed later, 
have been differentiated from the bark tissue. In the axis of this first leaf may 
be seen the meristematie position of the fu'st lateral bud /" A';; jwhieh ])ushes 
out the i^reen leaf hint; in front of it with its already clearly de\eloped e[)i- 




Fig. 10. Cross-section lhroui;li tlie lowest node of a youny rye plant. 
lOxpla nation ol" lettering in text, (t)rig.) 

dermis (c ) ; e is the epidermis of the sheath leaf which is already being 
differentiated from the axis. If the (dotted) tissue of the bud of the first 
green leaf (hi) be traced backward in this cross-section toward the side 
marked [' it is seen that this passes over into a colorless tissue ring char- 
acterized, however, by its comparatively large intercellular spaces contain- 
ing air (i) ; the bark tissue of the young blade. It is seen from this that each 
grain leaf is a direct continuation of the bark of the blade. This bark ring 



PART II. 



MANUAL 



OF 



Plant Diseases 



BY 



PROF. DR. PAUL SORAUER 



Third Edition—Prof. Dr. Sorauer 

In Collaboration with 

Prof. Dr. G. Lindau And Dr. L. Reh 

Private Docent at the University Assistant in the Museum of Natural History 

of Berlin in Hamburg 



TRANSLATED BY FRANCES DORRANCE 



Volume I 
NON-PARASITIC DISEASES 

BY 

PROF. DR. PAUL SORAUER 

BERLIN 



WITH 208 ILLUSTRATIONS IN THE TEXT 



^^^ 






Copyrighted, 1915 

By 

FRANCES DORRANCE 



L^ 



©CI,A401186 

THE RECORD PRESS 
Wilkes-Barre, Pa. 

MAY 29 1915 



115 

is connected on the side V with the tissue of the sheath leaf and it is worth 
noting that this sheath, even in so young a stage of blade differentiation, must 
have finished its work since the tissue is entirely impoverished and begins to 
be full of holes (I). 

While therefore in the Gramineae the accessory apparatus, which with 
too deep sowing brings the vegetative tip into the abundantly aerated par- 
ticles of soil, consists in the elongation (observed up to 9 cm.) of the lowest 
internode and, in case of necessity, also of the one above it, we find in the 
Leguminoseae and other dicotyledons a different arrangement. In beans, 
for example, we notice first of all an increased elongation of the hypocotyle 
corresponding to the need, so that finally, with very different depths of sow- 
ing, the growing tip of the stem in all plants is found at approximately the 
same height. Naturally the strength of the plant from the same kind of seed 
is decreased as the depth of sowing is greater. The more the hypocotyle must 
be lengthened, in order that its upper part, comparable to the curved back 
of the burden-carrier, can break through the load of the soil and bring the 
cotyledons to the light, the more reserve substances will be used up. It is 
therefore very evident that plants coming from greater depths are weaker 
even if they have not lost reserve substances in the seed through strong 
intra-molecular respiration. Such will be the case, however, if continued wet 
weather sets in after too deep sowing so that a shortage of oxygen results. 

The experiments by Godlewski. and Polzeniusz^ show what amounts of 
reserve substances can be lost through intra-molecular respiration and the 
formation of alcohol. Sterilized peas, in evacuated air, produced in the first 
period almost as much carbon dioxid as in normal respiration in the air. 
The whole amount exceeded 20 per cent, of the original dry substance of the 
seed. The amount of alcohol formed corresponds to that of the carbon 
dioxid. Only during the sixth week did the production of carbon dioxid 
cease in the peas which lay in sterilized water and up to that time possibly 
40 per cent, of the dry substances present had been broken down to alcohol 
and carbon dioxid. This is also the case in grains. In grains the action of 
the secondary roots on the nodes of the stem counteracts this weakening. 
In legumes a similar process of self assistance can now take place, since, as 
Wollny proved, adventitious roots are formed from the over-elongated 
hypocotyle member. He observed this on the parts of the stem which had 
been covered with soil, not only in field beans, but also in peas, sweet peas, 
lentils, lupines and plants of other families, — rape and sunflowers. But the 
legumes often are not capable of using such an accessory apparatus since, 
with normal depth of sowing and capacity for germination, they easily suc- 
cumb to other dangers which will be described in the section on "condition 
of hard shells." 



1 Godlewski und Polzeniusz, Ueber Alkoholbildung: bei der intramplekularen 
Atmung- hoherer Pflanzen. Anzeig. Akad. d. Wiss. Krakau, cit. Bot. Jahresb. 1897, 
p. 142. 



ii6 

Roots From the Tip of Grain Seeds. 

It seems best to add here an account of a case which, because of its 
pecuHarity and rareness, deserves a permanent place in science. 

The agricultural teacher, Wolfes in Dargun (Mecklenburg-Schwerin), 
sent me in 1876, fourteen wheat grains in which, through hypertrophy, the 
embryo did not lie to one side of the endosperm, but occupied a middle 
position. The grains were sown in the fall and in the spring they had partly 
rooted but without developing plumules. They were either slender, pear- 
shaped or even cylindrical at the one end, tapering rapidly at the other like 
the neck of a violin. In many grains (Fig. 11-12) tlie elongation of the 
slender end opposite the embryo was so marked that a neck was formed, 
possibly 2 to 3.5 mm. long, and twisted toward the upper end. 

In twelve grains the length of which varied from }i to ij4 cm. the 
neck bore a large number of very thin, thread-like roots i to 2 cm. long, 
closely arranged like a brush. These were pubescent almost their entire 
length. 

Upon attempting carefully with a needle to raise the wrinkled and oc- 
casionally ruptured testa of the grain it was found to be closely attached to 




Fig. 11. Wheat grains with roots not originating- from the embryo but springing 
from the hypertrophied testa at the tip of the seed grain. 

the grain in different places and, when broken off, was usually of a darker 
color. On the other hand its upper part was firmly connected with the beak- 
like growth along almost its whole length and could be raised from the grain 
proper like a straw cap (Fig. 12). The neck therefore at the time of the 
investigation was not connected with the actual grain except by the testa 
from the substance of which it also seemed to be formed. In the fresh con- 
dition of the grain this had been firmly set on the seed since various concave 
places on the inner wall of the cap, perceptible through the microscope, fitted 
on to the small convex elevations visible on the seed grains. 

There was another equally noteworthy phenomenon, namely, that the 
fissure, normally present, was lacking in these wheat grains. The grain, 
which had been dug up, also failed to show the seedling which lies at the base 
of the normal grain and is easily recognizable through the seed coat; it was 
not noticeable in the seeds observed. The endosperm itself, when cut apart, 
finally showed only a small degree of the white color of the healthy grain. 
There were long, glassy, translucent and yellowish streaks extending from 
the edge, inward. It had a rancid odor. The blue iodin reaction for starch 
was strong only in those particles of the grain which, on the freshly cut 



117 




Fig. 12. Wheat grain with hypertrophied testa and root formation at its tip. Embryo 
central instead of lateral. Explanation of letters in the text. (Orig.) 



ii8 

surface, were found to be white and mealy, while on the glassy places there 
was only a slight reaction. 

The glutinous layer in the Mecklenburg grain was not developed at all, 
the thin seed shell only incompletely. In place of this glutinous layer (Fig. 
12 k) a plate-like parenchyma was found, the content of which did not 
differ essentially from that of the underlying tissue. 

The most striking thing connected with this abnormal wheat grain was, 
however, the position of the embryo on the opposite end from that which 
bore the roots (Fig. 12 iv) and exactly in the middle of the grain (as in 
Typhaceae) equally surrounded on all sides by the tissue of the starch- 
containing endosperm. While in the normally constructed wheat grain the 
seedling lies without, at the base of the grain, and is connected with the 
endosperm by a special organ, the scutellum (the cotyledon), the seedling 
lies here (Fig. 12 e) without cotyledons in a central cavity (Fig. 12 h) of 
the grain. 

This cavity in some of the grains is elliptical, in others triangular. In 
some it extends possibly to the middle of the grain, in others, becoming 
narrower and narrower toward the top, it reaches to the tip, even penetrating 
into the tissue of the cap. On the inner side it is lined with a layer formed 
of two plate-like rows of cells of a glutinous content (Fig. 12 a) which 
clearly resembles the glutinous layer deposited in healthy grains outside the 
endosperm. 

The young leaves of the seedling, folded over one anotlier, show no 
essential variation. On the contrary, the number of secondary roots formed 
in whorls at almost equal distances (Fig. 12 r) steadily increases up to 6 to 8 
and these roots appear to be covered by a parenchymatous layer arranged in 
the manner of cork cells, 6 to 8 cells thick and free from starch. 

On this tissue lies the combined and modified seed coat (Fig. 12 sf) 
which in dry grain becomes thicker walled with more abundant cells toward 
the tip and develops imperceptibly into the cap which the root bears at its 
tip (Fig. 12 w). 

The vascular bundle is continued into the cap from the roots. Here are 
often found several bundles united at the tip of the cap into a ring-like, 
thicker network of ducts running horizontally and resembling a node of the 
stalk. 

Still further back from the tip these vascular bundles (Fig. 12 g), iso- 
lated near the outer edge of the inside of the cap, are seen to run backward 
(Fig. 12 gg). The endosperm normally has no fully developed vascular 
bundles and the cotyledons only embryonic ones. Here, however, the vas- 
cular bundles take an often irregular course through the endosperm and, 
in the individual grains, surround the seedling in a semi-circle and have 
not developed even though the grains lay in the soil over winter. 

By cutting cross-sections from the diseased grains and submitting 
them to microscopic investigation, the probable cause of this striking mal- 



119 



ffiTn 



formation was seen at once. The inability of the seed covering to free itself 
entirely from the grain was due to a connected firm, homogeneous, some- 
what dark mass (Fig. 13) ; the presence of thick, much ramified mycelial 

threads, often provided 
with short skein-like groups 
of branches, could be 
proved. The threads of the 
colorless, strongly refrac- 
tive mycelium grew trans- 
versely through the very 
thick walls (Fig. 13 m) of 
the fruit cells and seed coat 
which had been merged into 
one another. The mycelial 
threads grew more thickly 
when the cells were richer 
in content and thinner wall- 
ed, entirely filling some cells 
of the endosperm (Fig. 13 
mm). 

Near such places the 
starch had been dissolved 
and the cytoplasm had be- 
come solid as if it had been 
dried. In other cells a firm 
network of protoplasmic material scarcely distinguishable from starch could 
be seen. These were almost imperceptible in the starch grain but yet were 
there. This substance was apparently deposited about the starch grains but 
upon examination there were no grains 
present, only the corresponding cavities. 
In some such way originated the yellow- 
ish, translucent places between which 
lay groups of cells especially rich in 
mixed regions gave the 
reaction under a weak 



starch. These 
proper iodine 
magnification. 

The variation in the structure of the 
diseased grain is best shown by compar- 
ing figures 13 and 14. The latter repre- 
sents a section from a corresponding 
part of a healthy gain. The seed coat 
(Fig. 13-14 fs) in the diseased grain is more than three times as thick as in 
the healthy grain. In the abnormally developed seed coat there is a com- 
pletely developed vascular bundle with a clearly recognizable sheath (gs). 
In the diseased grain the growing fruit membrane passes directly over into 




Fig-. 13. Hypertrophied testa traversed by mycelia. 




Fig-. 14. Normal fruit and seed 
membrane together with the gluti- 
nous layer. 



the endosperm (e), and in the heakhy one the gluten layer (Fig. 14 ^)lies 
between the two tissues. 

Investigations of such grains in the "imported" seed show a similar 
condition. The seeds seem malformed and the fact that the malforma- 
tion manifests itself in the position of the embryo as well as in the develop- 
ment of the endosperm and especially in the thickened growth of the seed 
coat proves that this malformation must have been completed when the 
grain was forming in the head. Fertilization has nevertheless taken place 
normally since the embryo displays leaves and growing point as well as roots 
(the latter in increased numbers). But some local stimulus must at once 
have incited a cell increase in the fruit tissue and thereby displaced the em- 
bryo from the side towards the middle of the endosperm. This stimulus 
was active during the whole development of the seed and increased the vege- 
tative activity so that the character of the endosperm underwent a change, 
for the vascular bundles are those of a vegetative axis. We observe a most 
important numerical increase of the cells in the tips of the seed, assuming 
the character of a vegetative axis and, by means of the entangled vascular 
bundles, resembling a stalk node. Abundant roots develop at these stalk 
nodes 'and it is not improbable that leaf buds might have begun had there 
been a greater aeration of the soil layers. We would then have had a case 
similar to that in dicotyledonous plants when, as has often been observed, 
vegetative axes develop from their fruit nodes. 

.For such processes, however, the seed lay too deep. There was no ac- 
cessory apparatus for raising the seed to the upper surface of the soil, such 
as the elongation of the first internode in the seedling. As a result bacterial 
decomposition followed, due to the lack of oxygen, as was shown by the 
rancid smell of butyric acid. 

This is the reason for mentioning the -present case here. Had it been 
possible to determine exactly the causative fungus the case w^ould have be- 
longed under parasitic diseases. As it was impossible to make the my- 
celium fruit, the case becomes hypothetical as to the nature of the parasite. 
Only one thing is certain^viz., that the stimulating mycelium did not belong 
to the black fungi (Cladosporium, etc.). According to Brefeld's latest in- 
vestigations on the penetration of the smut into the blossoms, it is highly 
probable that the smut spores, which have entered the blossom, germinate 
soon after the fertilization of the grain, and by the slow advance of their 
mycelia have exerted the stimulus on the seed coat. 

3. Greater Horizontal Deeeerences. 

The individual development within the same plant species is influenced 
by horizontal changes in the place of cultivation from north to south, or east 
to west, as well as by the vertical elevation of the habitat. De Candolle^ laid 



1 Sur la methode de sommes de temperature appliquee aux phenomenes de 
vegetation. Separatabzug der Biblioth^que universelle de Geneve 1875. 



121 

down the principle that with approximately equal latitude and elevation, the 
temperatures above 0° in shade are higher for the same developmental 
phase (time of blossoming, defoliation, etc.) in the western parts of Europe 
than in the eastern ones. Observations show that in Europe the length of 
the growth period decreases toward the northeast and increases towards the 
southwest. Because of the many mountain chains and plateau-like inter- 
ruptions the phenomenon is less clearly evident in western Europe than on 
the great level plains of Russia. Kowalewski's^ very remarkable work re- 
ports on this phase. This is based on the statements of 2200 agriculturalists 
scattered throughout all parts of European Russia, who had reported the 
time of sowing and harvesting of the grain. Since cultivation must be 
adapted to climatic conditions, the usual times for sowing and harvesting 
show the existing vegetative conditions. 

The sowing of winter rye takes place in the southern part of the Gov- 
ernment of Kherson on the 15th of September-, at Archangel, on the first of 
August. The localities of simultaneous plantings of winter rye do not run 
parallel to the degrees of latitude, but are inclined from N. W. to S. E. ; 
therefore, they run almost in the same direction as do the isocheims. The 
difference in the time of harvesting winter rye in the far north (Archangel) 
and in the south (Kherson) extends, like the time of sowing, over a month 
and a half. The seeding period for summer grain in the far north is one- 
third to one-fourth as long as at the southern limit. At the western it is two 
to two and a half times longer than at the eastern. The time of harvesting in 
the north is likewise one-third as long as in the south ; in the west once and 
a half to twice as long as in the east. The localities of simultaneous ripen- 
ing of summer grain run from S. W. to N. E., corresponding therefore in 
their direction with the isotheres. 

The growth period in southern and southwestern Russia is only 85 to 
no days for rye, buckwheat, flax and barley,- — but no to 125 days for sum- 
mer wheat, millet, oats and peas. Sugar beets, maize and potatoes have the 
longest growth period, — 150 to 165 days. Thus, in the south, the longest 
growth period is almost twice as long as is- the shortest. On the other hand, 
in the north, the periods concerned are not only shorter everywhere but are 
also more simultaneous. In the far north and northeast the difference be- 
tween the longest and the shortest growth periods does not exceed 10 to 20 
days. 

For the same cultivated plant, in European Russia, the rate of develop- 
ment increases on the average with the latitude. Thus, for example, oats in 
the Government of Kherson (south) have a growth period of 123 days, 
wheat and barley one of no days. In the north, however, (Archangel) the 
growth period of oats decreases to 98 days, that of wheat to 88 days, of bar- 



1 Kowalewski, W., Ueber die Dauer der Veg-etationsperiode der Kulturpflanzen 
in ilirer Abhangigkeit von der geographischen Breite und Lange. Arb. d. St. Peters- 
burger Naturforscherges., XV, 1884 (russisch), cit. Bot. Centralbl., 1884, No. -^1, 
p. 367. 

- All dates are given old style as still used in Russia. 



12.2 

ley to 98 days. In the same geographical latitude, a longer vegetation period 
is found in the west than in the east. 

The causes of the shortening of the growth periods, therefore, cannot 
lie in the warmth which the plants receive at a corresponding degree of lati- 
tude, for otherwise the plants in the south would have passed through their 
development considerably more quickly than in the north, also since the 
southern black soil is raised to a higher temperature than the heavier, often 
clayey and damp soil of the north. Besides this, the lack of moisture in the 
south hastens maturity very greatly. Some other factor must therefore be 
determinative. Kowalewski states this to be the length of the insolation. 
He now assumes May 5th to be the mean time for sowing oats and August 
20th as the mean time for harvesting them, finding thereby an insolation 
period of 2000 hours for the 98 days of vegetation in Archangel. If the 
period of bright nights be added to this, there is an increase amounting to 
2240 hours. Kherson oats are sown on March 20, harvested on July 20th. 
In this 123 days of vegetation, however, only 1850 insolation hours obtain. 
Further, as Kowalewski says, it must be noted that the cultivated species of 
the north are adapted to a lesser degree of warmth. Therefore, when 
brought to the south, they ripen comparatively earlier. This result agrees 
with the one found by Schiibeler^ which will be mentioned later. Similar 
observations are said to have been made in Canada also. 

In further explanation of the change in the length of vegetation, Kowa- 
lewski brings forward the greater intensity of illumination, the small cloud 
masses and the greater humidity of the atmosphere and, supported by Fa- 
mintzin's investigatjons, he believes, for example, that the hght optimum 
for assimilation is exceeded in the south and therefore has a retarding in- 
fluence. This would correspond to the yellowing of the shade-loving plants, 
when grown in high mountains. It is not necessary to fall back upon the 
theory of the retarding action of the southern excess of light, if Wiesner's 
theory be accepted. In explaining the utilization of light on the part of 
plants in the far north, Wiesner- emphasizes, according to his investigations, 
the fact that in regions of the far north (Tromso), with an equal elevation 
of the sun and an equal clouding of the sky, the chemical intensity of the 
daylight has been shown to be greater than in Vienna and Cairo, but less 
than in Buitenzorg in Java. The light factor of the far northern regions is dis- 
tinguished in its illuminating quality by a relatively marked equability which 
obtains in no other locality where plants flourish. The plants of the arctic 
vegetative zone receive the greatest amount of light as a whole. Here, in 
the low growing plants there is no self-shading due to their own foliage, 
and even woody plants in adjacent southern regions show only a minimum 
amount of shade-producing branches. 



1 Schiibeler. Die Pflanzenwelt Norwegens. 

2 Wiesner, J., Beitrage zur Kenntnis des photo-chemischen Klimas im arktis- 
chen Gebiete. Sitz. Akad. d. Wiss. Wien CVII, cit. Bot. Jahresb. 1898, I, p. 586. 



123 

Wittmack has reviewed earlier cultural experiments as to the behavior 
of plants indigenous to any given locality when artifically introduced to a 
region farther south^. His conclusions follow; — plants from the north de- 
velop somewhat more slowly in middle Europe, catch up later with the in- 
digenous ones, however, or even exceed them. It is evident, therefore, that 
the short growth period, which has become habitual in the north, is often 
still more shortened by the increased warmth of the southern habitat, pro- 
vided also that the climate be dry. The damp climate of England with its 
low maximum temperatures retards ripening. The humidity of the air is a 
factor of great power and can delay ripening; just as, conversely, regions 
with great periods of drought, the climate of the steppes and similar con- 
ditions, not dependent on tbe degree of latitude, form limited centres where 
plants ripen prematurely. Too great drought certainly retards development, 
as has been determined experimentally. Stahl-Schoder's experiments, cited in 
the chapter on "Excess of Water," treat of soil dryness. The period of the in- 
fluence of heat is very important and is indeed expHcable. Heat in July and 
August is more advantageous than in May and June but the reverse is true 
for rain. 

Wittmack's summary in general shows the significance of the physical 
structure of the soil in relation to the early ripening; — that the vegetative 
time in eastern regions is shorter for the same varieties of grain than in 
western ones. 

Based on the observation that the varieties cultivated in northern 
climates retain their shorter growth period in the immediately following 
developmental periods, an active trade in northern seed has been developed. 
Meanwhile the quantity of the harvest should not be lost sight of. Abundant 
supply of nutrition being uniformly assumed, the quantity depends always 
on the length of the vegetative period, — i. e., the time of the formation of 
shoots. The longer time the grain has for the formation of vegetative 
organs (as in damp, cool seasons) the more abundant is the growth of 
shoots and with it the formation of a greater number of ears from the in- 
dividual seeds. 

H we should carry into the east varieties produced in the west, which 
are long-lived and characterized by great productivity, we would run the 
risk of frosts. This is most strikingly true in the English varieties of wheat, 
from the squarehead group, which toward the east come less and less true 
to seed, because they winter kill. Experience shows in regard to frost-resis- 
tance, that seeds from northern regions give plants in southern latitudes 
M-hich at times not only ripen earlier, in spite of an initial retardation, but 
also better withstand frost. 

From the result of Schiibeler's^ observations, it should be emphasized, 
that the quick growth, which has become habitual in northern or Alpine 

1 Ueber vergleichende Kulturen mit nordischem Getreide, Von Dreisch, Kor- 
nicke, Kraus, Vilmorin and others, referred to by Wittmack. Landwirthsch. Jahrb. 
1875, p. 479, and 1876, pp. 613 ff. 

2 Schiibeler, Die Pflanzenwelt Norwegens, 1873, pp. 77 ff. 



124 

climates because of a short vegetative period, is lost after four or five years 
of cultivation in lower latitudes. Conversely, long-lived varieties accustom 
themselves in a few years to a short vegetative period. Yellow chicken 
maize from Hohenheim, for example, which ripened in 1852 at Christiana 
in 120 days after repeated sowings, shortened its growth period to the extent 
of 30 days in 1857. In Christiana the developmental period of barley is 90 
days, but seed brought from Alten (the 70th parallel) needed only 55 days 
(see Kowalewski). 

Of the chemical properties developed in a northern habitat, which in 
great measure correspond to the changes in plants in high elevations, the 
fact that the sugar content of the fruits decreases toward the north while 
the aroma increases is of especial importance. Bonnier and Flahault main- 
tain also that not only the size of the leaves increases in the darkness of the 
north but also their green color^ Schiibeler's experiments in summary- 
give the following special examples : — In wheat brought from Ohio and 
Bessarabia, the grain became darker in color each year until it was as yellow 
brown as the native Norwegian winter wheat. Similar results were obtained 
with maize, beans, peas, celery, etc. Celery taken from a region extending from 
the Caucasus to Hindustan, grows in Africa (Egypt, Abyssinia and Algeria) 
and may be found in Europe from the Mediterranean to the Baltic ; it now 
extends even into Finland up to the 69th parallel. There, however, the root 
stalks are poorly developed; — the aroma, nevertheless, becoming more 
pungent^. The greater intensity of color in the blossoms, as already men- 
tioned, a peculiarity shown to correspond with an increasing elevation above 
sea-level, also appears in most garden flowers as cultivation advances to- 
wards the north. In regard to the formation of aromatic substances, be- 
sides celery, juniper may also be cited as an example. In Norway it is much 
richer in oil than in Central Europe. Onions also and garlic are uncom- 
monly pungent in Norway. Strawberries are sour but aromatic, while, 
according to Gotze, they are exceedingly sweet in Coimora, but almost with- 
out any aroma. Plums often remain so sour that, compared with fruit 
brought from more southerly regions, they still seem immature. A similar 
condition exists with grapes as shown by comparing the sweet Portugese 
grape with the less sweet but aromatic Rhenish grape. 

In considering the horizontal differences, expressed in the decrease of 
rainfall and increase of clearness of the air, from the west towards the east, 
in the conditions of light between southern and northern regions etc., we 
should not forget one circumstance, to which de Candolle* has already 
called attention. This, to be sure, has not been sufficiently verified experi- 



1 Bonnier et Flahault, Observations sur les modifications des vegetaux suivant 
les conditions physiques du milieu. Annal. d. sc. nat. Botanique, t. VII, Paris 1S79, 
p. 93. 

2 The effects of Uninterrupted Sunlight on Plants. Gard. Chron. 1880, I. p. 272. 

3 Hansen, C, Der Sellerie. Gartenflora, 1902, p. 18. 

4 de Candolle, A., Sur la methode des sommes de temperature appliquee aux 
phenomgnes de la vegetation. Archiv. des sc. physiques, etc. Nouv. ser. LIU. LIV. 
Genf 1875, cit. Bot. Jahresber. 1875, p. 585. 



125 

mentally, but finds repeated substantiation in practical experience. It is 
namely the greater, more complete dormant period of plants. According to 
Thne^, trees which thrive normally in Central Europe and in Coimbra put 
out their leaves possibly a month earlier in Coimbra and their autumnal 
change of color occurs about a week and a half later than with us. Thus 
their dormant period is about six weeks shorter there. The length and com- 
pleteness of this dormant period, however, must influence greatly the rate 
of subsequent development. It may indeed be assumed that, with the con- 
tinuation of a temperature which does not stop the functions entirely, a 
number of vegetative processes continue with a slow but steady consumption 
of materials (process of oxidation) and without any compensation to the 
plant through newly assimilated substances. Besides this, it seems that 
many enzymes, which affect the energy of metabolism, either succeed in de- 
veloping to the necessary amount only during a complete dormant period, 
or are made ready for it. If no complete rest takes place it may be observed 
especially in the two or three year old bushes and in the buds on branches 
of woody plants. These are forced earlier and produce w^eaker organs 
(smaller leaves, a greater number of sterile blossoms). 

The increased weight of the seeds in northern latitudes has already 
been considered. There are, however, some experiments by Petermann- 
which prove a higher germinating pozver of Swedish seeds of clover varie- 
ties, timothy (Phleum pratense L.J, and of spruces and pines as compared 
with German, French and Belgian seeds. The Swedish seeds, which 
actually, on an average, possess a greater weight, show greater power of 
germination, not only in the number of fertile seeds which can germinate, 
but also in the energy with which germination takes place. These results 
may be explained very well by a greater developmental energy in the plants, 
due to a more complete winter rest. 

These observations have a very noteworthy practical bearing in so far as 
they affect the culture of seeds obtained in exchange. It is not enough 
merely to introduce seed from other regions, but it will seem necessary lo 
ask above all, what characteristics it is desired to improve in the cultivated 
plant and in what climates these characteristics attain a higher development. 
Taken from such localities the seed will then give the desired results. 

The cultural results, obtained by using plants of other climates, hold 
good as a rule, however, only for a very few growth periods. Often the in- 
fluence of the present habitat is felt in the second generation when the plants 
of foreign importation have assumed the habits of the native varieties. 
Fruit trees taken from Angers grew and bloomed on Malorka even at the 
end of February, while the native ones did not blossom until a month later^. 
A shipment made two years later from Angers showed the same phenom- 

1 Ihne, Phanolog-ische Mitteilungen. Cit. Bot. Jahresb. 1898, II, p. 409. 

2 Petermann, Recherches sur les graines originaires des hautes latitudes. 
Extrait du t. XXVIII. des Memoires couronnes et autres Memoires publies par 
I'Acad. Royale de Belgique, Bruxelles, 1877. 

3 Gartenzeitung von Wittmack, 1882, p. 374. 



126 

enon. The fruit trees of the first shipment were now, however, blossoming 
later, i. e., simultaneously with the native ones. The transition from the 
hereditary form of growth to the new one determined by the climatic con- 
ditions is rarely effected as rapidly as it is lost when returned to its former 
habitat. Yet, in our vegetables, we have examples of a rapid change in 
pecularities. In a tropical climate these keep approximately their own char- 
acter only in the first year. Already in the second year the seeds of these 
imported plants produce elongated, lignified specimens\ These are our cul- 
tivated forms which are beginning to vary from the normal. No rapid 
changes are noticeable in species growing wild, as has been shown by Hoff- 
mann's experiments with parallel seeding of certain forms of Phaseolus 
and Triticum in Giessen, Genoa, Montpelier, Portici and Palermo-. On 
the other hand, Hoffmann mentions slow changes, first taking place in the 
course of many generations. Thus Ricinns communis becomes tree-like and 
perennial in the tropics, in the same way Reseda odorata becomes more or 
less persistent in New Zealand and, conversely, Bellis perennis becomes an 
annual in St. Petersburg. 

Among the changes in mode of growth, which are only slowly com- 
pleted, belongs the formation of the annual rings in our trees. At any rate 
the distribution of vascular spring wood and the slightly vascular summer 
wood within the same degree of latitude fluctuates in each year according 
to the amount and distribution of precipitation. But in the changes 
of the average weather, due to changes in latitude, the same dif- 
ferences become constant and form thereby ecological varieties. Bonnier^ 
treats thoroughly such anatomical differences in the development of the 
same species in northern and southern positions. He compares examples 
of the linden, red beech, acacia and others from the region of Toulon (with 
its 260 days of active growth) with those at Fontainebleau (growth period 
178 days) and found that the spring wood develops better in the south, 
having more abundant, often wider ducts. In this the abundance of precipi- 
tation in the spring in the Mediterranean district surely has a definite bear- 
ing. The summer wood of the south, however, is richer in libriform fibres 
and often consists only of these, while at Fontainebleau numerous ducts are 
formed, even in summer. The leaves of the Toulon plants were shown to 
be one-third to one-half thicker and provided with more layers of palisade 
parenchyma in comparison with the plants grown in the north. The stomata 
are more numerous, the sclerenchyma is greater and the cuticle strength- 
ened. The Toulon plants exhibit the character of Mediterranean flora in 
general. 

The greater intensity of the color of the blossoms, as the plants advance 
from the plains to the mountains and from lower latitudes to northern 



1 Deutsche Gartnerzeitung, 1883, No. 17. 

2 Hoffman, H., Ruckblick auf meine Variationsversuche von 1855 bis 1880. Bot. 
Z., 1881, p. 430. 

3 Bonnier, Cultures experimentales dans la region mediterraneenne, etc. Cit. 
Bot. Jahresb. 1902, II, p. 299. 



127 

regions, has already been considered. Recently attention has also been di- 
rected to the increased change of color in foliage leaves and its peculiar 
significance as a protective adaptation has been suggested. MacMillan^ 
treats of these conditions very fully. He speaks of "luarming-up colors" 
meaning especially the red coloring substances which are more abundantly 
represented in colder regions. Alpine and arctic plants are more often 
found with blue or violet blossoms than with yellow ; the ends of the twigs 
are often reddened. The temperature is somewhat raised by the red coloring 
matter and the influence of cold somewhat weakened. If one thermometer 
be covered with a green leaf and another with a purple one, while both are 
exposed to the sun, in a short time the thermometer protected by the purple 
leaf shows a rise of 6° to io° of temperature. In the same way he found 
that a thermometer, stuck in a bunch of violets, shows a higher temperature 
than one in a bunch of cowslips, after an equal exposure to the sun. 

The autumnal coloring may be conceived as a definite reaction of the 
plant to the lowered temperature. The plant provides warmth for itself in 
its red coloring matter. On this account so many spring flowers are red 
and violet and autumn flowers blue or red. 

In warm climates plants often assume peculiarities directly opposite to 
those of arctic or alpine plants. In tropical plants the storage cells are less 
strongly developed than in related species from colder regions. The buds 
are less protected, pubescent coverings more rare on leaves and twigs (with 
the exception of desert plants). Many winter habits disappear. There are 
fewer biennials. The warming-up colors recede m.ore and more, while 
white, yellow and spotted blossoms (Orchids) predominate. 

Nature would develop red coloring matter to prevent loss of the super- 
fluous light and to transform it into warmth and to use it as a stimulus to 
growth. 

We cannot support this theory of the premeditated. utility of the red 
coloring matter as an apparatus, producing warmth and weakening the 
light, even if we had such an inclination. If the red coloring matter has 
once been produced, it will be effective in the way given. The idea that the 
plant can produce it as a protection against cold, when the temperature be- 
comes lower, is not plausible, because in the hottest summer temperature 
leaves can be reddened. In the Rosaceae which are rich in tannin (Crataegus, 
for example), I have been able to produce the red autumnal coloring after 
a few weeks in the middle of summer by girdling the twigs. The fact that 
in summer the underside of many leaves, when reversed, becomes red within 
a few days is universally known. Parasites furnish further instances. On 
the same cherry tree, for example, the leaves of branches attacked by 
Exoacus Cerasi turn glowing red, while the healthy ones remain green. In 
many spot diseases the circular fungus centre appears surrounded by red. 
Amaryllidaceae, whose leaves die down in summer (Hippeastrum etc.). 
develop carmine spots and stripes. 

1 MacMillan, Conway, Minnesota Plant Life Saint Paul, Minnesota, 1899, p. 417. 



128 

Thus we believe that the red coloring matter may be looked upon as a 
necessary reaction of the cell to the influence of different factors connected 
with a relatively over-abundant supply of light. One of these factors may 
be the lowering of the temperature due to a change in the latitude or longi- 
tude of the place of growth. 

If we look back to the many changes undergone by the plants in their 
morphological and chemical structure because of any change in latitude of 
the place of growth, we cannot shut our eyes to the conviction, that not in- 
frequently in these changes of place may he sought the reason for a predis- 
position toward disease or, on the other hand, toward greater immunity. 

We have mentioned that the western squarehead wheat grown in 
eastern regions has greater susceptibility to frost and now remind the 
reader that parasitic diseases may also be dependent on the dift'erent mode 
of development of the host plant inherited in the seed. One should con- 
sider, for example, the fact that many parasitic fungi appear or are especial- 
ly abundant at definite periods. In case such fungi only attack young leaves, 
the presence of young leaves when the spores are ripening will determine an 
epidemic. The rapidity with which a plant passes through its develop- 
mental cycle in any given climate is a determining factor in this question. 
If it develops slowly, its leaves are young and remain susceptible for a longer 
time, giving a greater danger of fungus infection. If a variety matures 
quickly (for example, one introduced from more northern or eastern 
regions) then the leaf may be fully matured at the time of the actual distri- 
bution of the spores and therefore be resistent to many parasites. 

Such circumstances deserve greater consideration than has been given 
them as yet. They will also be a factor in the discussion of the "biological 
races" of individual parasites, for it is most probable that often infections 
of the most closely related host species fail because the host plant at the 
time of infection is already in an advanced developmental stage, in which 
the leaf is more mature, i. e., has thicker walls and less cell-content. The 
fact that the fungus infection is connected with a definite developmental 
stage of the host plant is shown, for example, in the rust fungi of grains. 
Eriksson^ states that the rust occurs earlier in the varieties ripening early 
and recent observations show that the different forms of Puccinia have defi- 
nite periods for attacking grain. Thus it was shown in 1904- that Puccinia 
glumarum appeared first and foremost in wheat, then followed P. dispersa 
which, however, attacked only those organs and varieties which were still 
immature. Later, slowly ripening varieties of wheat were found badly at- 
tacked by P. dispera and slightly by P. glumarum, while the converse is 
true for varieties maturing early. P. graminis was found in stored grain. 



1 Eriksson, J., Sur I'origine et la propagation de la rouille des cereales par la 
semence. Ann. scienc. nat. Bot. VIII. ser, Vols. XIV. and XV. Paris 1902. 

- Jahresb. d. Sonderausschusses f. Pflanzenschutz. Deutsche Landw. Ges. 1905 
Getroiderost. 



129 

Glassy Graix Kernels. 

These must also be considered, as the result of climate influences. 

Grains are called glassy when their endosperm is hard, almost trans- 
lucent and grey or reddish in cross-section, while in the normal mealy 
kernel the endosperm appears soft, white, porose and easily friable. . 

This glassiness of the kernels occurs usually more abundantly in the 
north and east of Europe than in the west, which fact points to the influence 
of atmospheric dryness with a higher light intensity. Tn damper, western 
regions the vegetative organs obtain a greater ascendancy. Thus Lieben- 
berg^ states, for example, that the otherwise excellent northern barley has 
two disadvantages ; — viz., too large a percentage of glassy grains and too 
dark a color which is caused by rain falling on the grain when ready for 
harvesting. These gusts of rain at harvest time naturally play no part in 
the development of grains which mature during the dry season. With the 
lengthened light action, varieties of rye also become intensively colored. 
The same author reports that at the grain exhibition in Sv.eden, the oat 
samples, on an average, possessed only 22.66 to 32.04 per cent, of chaff by 
weight, while in the Austrian and French varieties it fluctuated between 
25.23 and 38.37 per cent. In general there is truth in Haberlandt's- state- 
ment, that a continental climate produces glassy grains, but that, on the 
other hand, cool, wet summers or an artificial abundance of nutritive sub- 
stances and water produce mealy, specifically lighter grain kernels, poorer 
in nitrogen. 

The glassy condition of the grain, according to Gronlund's"' investiga- 
tions on mealy and glassy barley, exists in the fact that the cells of the albu- 
men in the mealy grain which contain the starch show that the spaces 
between the starch cells are filled with cell-sap, while in the glassy grains 
these spaces are filled with protoplasm. Johannsen's'* work assumes a 
greater air content not only between the walls of the mealy grains, but in 
their whole mass. In germination, the glassy grains become mealy. Ac- 
cording to Gronlund, who, moreover, acknowledges no relation between 
weather and the production of the glassy conditions, glassy kernels germi- 
nate more easily and better and give stronger plants. Although he assumes as 
mcontestible that glassy kernels may be produced from soil containing much 
nitrogen, yet he believes that poorer, sandier soil, poorly cultivated, pro- 
duces this peculiar formation much more certainly. He found that mealy 
grain was produced by pure potassium fertiliaafion. Moreover, both forms 
occur at times in different stages in the same head. I would like to assume 
for the production of glassy kernels that the process of starch formation is 



1 V. Liebenberg-, Bericht iiber die allgemeine nordische Samenausstellung etc., 
1882, cit. Bot. CentralbL. 1882. No. 43. p. 115. 

- Habeiiandt, Die Abhangigkeit der Ernten von der Grofse und Verteilung- der 
Niedei'schlage. Oesterr. landw. WocbenbL, 1875, p. 352. 

3 Nach einer Preisscheift des Verf. cit. im Jahresbericht f. Agriculturchemie 
XXIII (1880), p. 214. 

4 Allg-. Brauer- und Hopfenzeitung, 1884, Nos. 78 and 79. 



130 

shortened in sandy soil, which dries quickly, and, since potassium makes the 
corn mealy, I would much sooner believe that the action of the potassium is 
stopped too soon and indeed because other processes, viz., those of ripening, 
take place too early and too intensively. This will happen much more 
quickly with strong action of light and warmth and when the water con- 
tent is less. Sanio's^ statement that in East Prussia the glassiness of 
wheat is due to its becoming overripe on the stalk supports the theory of 
the predominance of the ripening process at a time when starch formation 
should be taking place. This opinion is analytically supported by R. Pott's 
investigations- who found on an average a higher percentage of ash in 
glassy varieties of wheat than in mealy kernels. The kernels, in the too 
rapid ripening, had not completely consumed the mineral substances in 
forming organic substances. Compare here the high percentage of nitrogen 
in the grains of oats plants, which suffered from a scarcity of water or 
from its excess (see chapter, "Excess of Water"). 

Petri and Johannsen'' have made investigations which throw much 
hght on the nature of glassy kernels. The former, as early as 1870, stated 
that glassy kernels, when softened by water, become mealy and the latter 
substantiated this observation. Two hundred kilos of barley were moistened 
with half that amount of water, until they had taken up 15 per cent. They 
were then dried immediately, spread and turned until the original weight 
was again obtained. The percentage of mealy kernels now" was 50 per cent., 
while in the original material it amounted to only 19 per cent. In cultural 
experiments it was found that, in early seeding, a mealier barley, poorer in 
nitrogen, had been formed, while in later sowing the harvested product was 
richer in nitrogen. This discovery indicates that in this glassiness of the 
kernels there is only a mechanical difference, which develops if ripening is 
very much hastened by a scarcity of water with an excess of light and 
\varmth. A gradual ripening process gives a longer time for developing an 
increased starch content with the retention of a larger water content in the 
substance which is later partially replaced by air. This refers especially to 
the protoplasm in the endosperm cells. The starch grains lie embedded in 
this. With quick ripening, the cytoplasm sticks close to the starch grains, 
making the kernels appear glassy. With slower ripening and greater water 
content the cell is more loosely constructed, while between the starch grains 
more cell sap and later more air are present, and then, because of the larger 
intercellular air spaces, the grain is opaque and mealy. As the protoplasm 
predominates, the tendency is toward glassiness, and on this account, even 
normally, the outer layers of the seed, as, for example, in maize, are glassy, 
the inner ones mealy. These conditions explain Schindler's observations* 
that, in wheat grains, mealy and glassy portions can alternate. 

1 Botanisches Centralbl., 18S0, p. 310. 

2 Jahresbericht f. Agriculturchemie 1870-72, II, p. 5. 

3 Johannsen, Bemerkungen liber mehlige und glasige Gerste (Ugeskrift for 
Landsmaend), 1887, cit. Biederm, Centralbl., 1888, p. 551. 

4 Schindler, Lehre vom Pflanzenbau auf physiologischer. Grundlage. Wien 1896. 



131 

The above explanation of the production of glassiness is substantiated 
by the experimental results, which have been obtained by the Deutsche 
Landwirtschafts-Gesellschaft^ The report states: — The glassiness of the 
kernels depends more on the conditions of growth than on the variety. 
Varieties with a shorter vegetative period are glassier — such as Lupitzer, 
Strube's bearded and Cialician club wheat in comparison to Schlanstedter 
and Noe wheat. The productive power of the varieties in general stands 
in inverse relaton to the glassiness of the grains. 

4. Continental and Marine Climates. 

The characteristic distinction of regions influenced by the ocean con- 
sists in the lesser fluctuation between summer and winter temperatures, — 
since the summers are longer and cooler, the winters warmer. We find that, 
under the influence of the Atlantic Ocean, spring comes earlier, while au- 
tumn is delayed longer than in regions with a continental climate. Yet the 
effect on vegetation is not the one expected, in spite of the earlier spring, 
for the blossoming time of wooded plants is at most only a few weeks 
earlier, because of a cooler spring temperature and the ripening of the fruit 
is scarcely earlier, indeed, it is often delayed and occasionally does not take 
place at all. Consider, for example, grapes which do not ripen out of doors 
in England. Throughout the year, the air is more moist and in the change 
of season extensive heavy mists often prevail. 

Haberlandt's opinion has already been mentioned, according to which 
early maturity of plants may appear with the same ease in northern latitudes 
as in southern ones, and thus lead to the production of con-esponding varie- 
ties. Conditions of humidity also act determinatively in this and all become 
evident in the great fluctuations in a continental climate in contrast to an 
uniformly damp coast climate. Haberlandt's culture experiments- gave 
results as follows. Seed brought from damp climates gives proportionately 
more straw, but less grain, — the grain is also more easily subject to lodging. 
On the other hand, in seed from dry regions, with a short spring and hot, 
dry summer, there is a production of less straw and greater grain crops, 
and plants from such seed better withstand drought. When exchanging 
seed it is more advantageous to take it from countries with a continental 
climate. The hard winters influence the grain product in such a way that 
the plants produced are less apt to winter kill than those which have been 
transplanted to the East from the moister west with its milder climate. 

The continental climate produces smaller but specifically heavier grain, 
while a cool and damp summer or an artificial abundant supply of water 
and food substances increases the size of the grain, to be sure, but at the 
same time causes more porous contents, since, instead of the glassy con- 



1 Mitteilungen der Saatzuchtstelle iiber wichtige Sortenversuche. Saatliste 
vom 6. Dez, 1914. Deutsche Landwirtseh.-Ges. 

- Haberlandt, Fr., Ueber die Akklimatisation und den Samenwechsel. Oesterr. 
landw. Wochenbl., 1875. No. 1. 



132 

dition, a mealy one appears, together with a decreasing specific weight and 
decreasing nitrogen content. 

Finally an important observation bearing on the exchange of seed is 
the fact that winter grain coming from regions above the 45th parallel 
of latitude and cultivated by us in the spring, does not produce shoots, while 
on the other hand, that taken from lower latitudes behaved with us like 
summer grain. 

Because of the great interest on all sides in the colonies, it is necessary 
to take tropical conditions into consideration. Here the differences of tem- 
perature on the land and between land and sea attain a greater significance. 
Thus, for example, Fesca^ reports, in regard to the great warming of the 
land in direct sunlight as compared with that of the sea, that the tempera- 
ture of the tropical ocean rarely exceeds 30°C. while the rock is heated up 
to 60° to 70°C. Pechuel-Loesche observed a soil temperature above 75°C. 
on the west coast of Africa in the 5th parallel of south latitude, not less 
than 36 times between January ist and March 4th. In contrast to this, 
however, stands the nightly cooling down to I5°C. and less. Daily fluctua- 
tions of the soil temperature from 30° to 40°C. are very frequent in the 
tropics while, on the other hand, the daily fluctuations of the sea might at 
most reach i°C. 

As a result of the dift'erences in the morning quality of land and sea, 
a low barometric pressure must be produced on land in the day with the in- 
tensive sunlight, so that the air from the sea streams in that direction and, 
conversely at night. These sea and land breezes are considerably more in- 
tensive in the tropics and sub-tropics w-ith the stronger contrasts in warm- 
ing land and water and form a factor to be reckoned with. According to 
Saito" the air above the sea is almost free from mould fungi, bacteria and 
yeast germs, while the air above the land (street and garden air in Tokyo 
was investigated) w^as especially rich in germs in wet and warm periods. 
Thus the sea breezes act as purifiers of the air. The sea breezes decrease 
towards the poles, since the sea gradually assumes a higher mean heat than 
the land and also because the daily fluctuations of the soil are less. 

For the same reason the changing annual winds, the monsoons, corres- 
pond to the periodic daily winds in the strong warming of the great conti- 
nents to which vegetation must adapt itself. 

The amount of precipitation occurring as rain depends also on the re- 
lation to the sea and the temperature and, accordingly, it is most abundam 
in a w^arm sea climate, scantiest in a continental one. An annual mean of 
9°C. approximately holds for all the German North Sea coasts. With an 
80 per cent, saturation, the air would contain 7.26 g. water vapor in a cubic 
meter. If the air cools down to 4°C. it can hold only 6.9 g. water vapor per 
cubic meter and the difference must therefore be eliminated as precipitation. 



1 Pflanzenbau in den Tropen und Subtropen, p. 23. 

- Saito, Untersuchunsen iiber die Atmospharischen Pilzkeime. Journ. College of 
Science, Tokyo. Vol. XVIII. 



133 

If tropic air reaches 25°C. with the same saturation (80 per cent.) it con- 
tains 18.48 g. water vapor and ehminates 1.18 g. water per cubic meter when 
cooled down to 5°C. This amount of precipitation therefore is more than 
three times that of air at 9°C. when influenced by the same decrease in tem- 
perature on the North Sea coasts. Thus are explained the heavy tropic 
rains and especially the heavy fall of deiv which, in places, must suffice for 
a certain period in hot climates as the only source of water. 

Just as in cultivation experiments, soil analyses and mean temperature 
offer no sufficient insight into a possible utilization of food substances on 
the part of cultivated plants, just so little can the annual rain fall indicate 
the moisture conditions of a region. For it depends essentially upon the soil 
conditions and the distribution of the precipitation in the different months. 
Over a greater part of the desert of Sahara (see Fesca) the same or a greater 
cmount of rain falls than that sufficient for Germany's agriculture (60 cm.) 
without its having there any essential effect. For, on a highly heated soil, 
moisture exaporates immediately. The most desirable distribution of rain 
in the tropics is not the one extending uniformly throughout the whole year, 
but, viz., at the beginning of the vegetative period an abundant precipitation 
and then a time of dryness. The abundant clouds in the rainy season con- 
tribute essentially to the production of a cooler temperature which is es- 
pecially favorable for the development of the vegetative organs. 

Along the coast the climate is cloudier than it is inland. In regions of 
great atmospheric dryness, as in the Mediterranean basin, often there is 
only 20 per cent, cloudiness as an annual average : in the dryest months often 
only 10 per cent., — in the moist tropics not infrequently more than 80 per 
cent. Since, however; the cloudiness decreases the taking up and giving off 
of heat, the temperature of the lower latitudes is less and that of the higher, 
greater. Many cultivated plants require these lower temperatures and 
cloudiness. We believe, with Zimmerman^ that many diseases in coffee plan- 
tations, especially the excessive production of fruit, may be due to insuf- 
ficient shading. In the same way it may be that the great susceptibility to 
fungous diseases which has appeared in the last 15 years^ since tea has been 
cultivated in the Caucasus, has been due in part to the difference of the 
Caucasian climate from that of the regions from which tea was introduced. 

The development of the plant body is of course adaptable to the climatic 
conditions and factors of growth. The m.ore recent biolog}^ takes these cir- 
cumstances into consideration as is shown by the work of Hansgirg^. He 
speaks of stenophyllus wind leaves (as in the willow type) ; of leather 
(coriaceous) and wind leaves (palm type) ; of xerophyllus leather leaves 
(Myrtus, Laurus), of dew leaf types (Bromeliaceae, Pandaneae) ; thick 



1 Zimmermann, Sonderberichte uber Land- und Forstwirtschaft in Deutsch- 
Ostafrika. Vol. I, Part 5, 1903. 

2 Speschnew, Travaux du jardin bot. de Tiflis VII, 1 Verhandl. d. Internat. 
landwirtsch. Congresses in Rom 1903. 

3 Hansgirg-, A., Phyllobiologie nebst Uebersicht der biologischen Blatttypen etc. 
Leipzig, Borntrager, 1903. 



134 

leaves (Crassula and mesembryanthemum types) etc. The most conspic- 
uous example is the vegetation of the sea shore with its halophytic character. 
Brick^ explains the fleshy and glassy constitution of the vegetative organs as 
due to the abundance of sodium salts, which makes the parenchyma ex- 
tremely turgid. 

The greater the number of examples showing the adaptation of the 
plant to climatic conditions, the more marked will be the untenability of the 
theory, that the climatic relations formed in each place of cultivation can be 
changed at will without causing injury. If the whole sum of the climatic 
factors should correspond in two widely separated localities this would be 
no guarantee that the given plant would thrive as well in the new home 
as in the old, since the distribution of light, heat and moisture can be proved 
to be very different in the different periods of growth. The diseases of the 
New Holland and Cape plants which, adapted to a dry climate, must pass 
their lives in our sunless, damp conservatories, give the most abundant 
proof. Decay of stem and root, dying of the twigs caused by Botrytis etc., 
constantly cause injuries to the successful cultivation of these plants. The 
so-called damping off of the shoots of Pimelea, Chorizema, Pulteneae, Cor- 
rea, Boronia, Agathosma, and Borosma, of Helichrysum, Humea etc., is a 
result of the great humidity in our conservatories which can not be over- 
come. 

5. Influence of Forests. 

The forestration of a locality modifies the influences of the position and 
soil constitution and to this point patholog)^ must pay especial attention. 
The influence of forests is like that of surfaces of water, for, since organic 
substances possess a higher specific warmth than do mineral substances, the 
overgrown soil will be cooler, with an equal exposure to the sun, than the 
naked rock or sand. The summer heat is also moderated by forests. With 
the abundant evaporation of the foliage, the air becomes more moist, the 
thicker the growth and the less motion in the air. Corresponding to the 
greater evaporation, there is a more abundant cloud formation over forests 
which is not so easily dispersed. Since the relative humidity of the air is 
greater in and above the forest, much more dew is formed. The force of the 
rain gusts is decreased. Since torrential rains, especially on slopes, cannot 
be taken up as quickly, the mass of water runs off from the naked earth 
and at the same time carries away the fine humus from the higher fields to 
the lowlands. The annual repetition of this process so changes the conditions 
of the fields that the higher places become impoverished and retain only a 
slightly fertile soil skeleton, while on the low lands the humus layers keep on 
growing. The power of the soil to retain water decreases with the loss of 
humus and injuries due to a scarcity of water show themselves. In heavy 
soils the steady beating of the rain drops in severe storms tends to form a 
crust. 



1 Brick, Beitrage zur Biologie und vergleichenden Anatomie der baltischen 
Strandpflanzen. Cit. Bot. Jahresb. 1888, I, p. 765. 



135 

All these unfavorable conditions are overcome by the forest, the tops of 
the trees catching the rain and partially retaining it. Nevertheless the water, 
which passes through and runs down along the trunks, is retained by the 
moss and the dry leaves in deciduous forests, forming the upper surface of 
the soil or the humus, thus becoming of benefit to the vegetation. Furst's'^ 
"Illustriertes Forst- und Jagdlexikon" gives some positive figures on these 
theoretical discussions. Based on the observations of the forest meteorologi- 
cal stations, it is stated that the temperature of the air in the annual average 
is possibly o.8°C. lower under the close roof of tree crowns of the forests, 
than in the open. The difference is greatest in summer (up to 3°C.) while 
it approximates the annual average in spring and autumn and almost dis- 
appears in winter. "The fluctuations in temperature are less under the 
shelter of the tree crowns than in the open." 

The temperature of the forest soil is from i to 3°C. lower at all seasons 
of the year than that of open land. The absolute moisture does not differ 
in the forest and in the open; but, on account of the lower temperature, the 
relative moisture in the forest during the winter, spring and autumn is from 
4 to 8 per cent, higher than in the open, and in summer from I2 to 20 per 
cent. The evaporation from a free surface of water in the forest is from 
50 to 60 per cent, less than in the open; "the evaporation of the water from 
the soil is reduced from 80 to 90 per cent." Of the precipitated moisture, 
10 to 50 per cent, will be retained by the crowns of the trees, according to 
the species, the age and dimensions of the forests as well as the amount of 
precipitation, and in light rains it often amounts to 100 per cent. In general 
60 to 80 per cent, reaches the soil in the forest. "In Central Europe 
the annual and the summer temperature will be lowered 1° and 2° to 3°C. 
by the dimensions of the forest and the relative moisture raised ca. 5 per 
cent, and 15 per cent." 

Since the amount of the distant action from extended forestration has 
not yet been determined, the question as to the influence of the forest on 
climate must remain open. But one effect of the foTest on the immediate 
vicinity cannot be denied and this phytopathologists must consider. 

Differences in insolation are felt slightly in the forest, but very 
quickly and strongly in the open field. The soil is warmer; the layers of the 
air lying above it must necessarily produce an equalizing air current which 
is most significant in spring when vegetation awakens. 

Hesselmann's- investigations give an insight into forest vegetation. 
He observed the regular dying of the twigs which takes place within the 
crowns of the trees and found that in birch and mountain ash the leaves 
were still strongly active in assimilation ; but in the hazle-nut markedly less 
so. If well-lighted branches die, phenomena of correlation are at fault. 
Trees which can live in shade develop distinct sun and shade leaves ; trees 



1 Illustriertes Forst-und Jagdlexikon, 2nd. Ed., revised by Dr. Hermann Fiirst, 
Berlin 1904, Paul Parey, p. 384. 

'^ Hesselmann Hendrik, Xur Kenntnis des Pflanzenlebens schwedischer Laub- 
wiesen. Jena, Fischer, 1904. 'Cit. Bot. Centralbl. v. Lotsy, 1904. No. 49. 



136 

which require Hght do not show this difference. The assimilation activity 
of the flora of the forest floor is ver}^ rapid in spring when the trees and 
trunks are still bare and decreases with the foliation more slowly in shade 
trees, because of their structure, until it finally ceases entirely. The respira- 
tory intensity decreases with the decreased "food consumption." Detached 
shade leaves of Convallaria majalis etc., form more starch in the sun as well 
as in the shade than do sun leaves treated in exactly the same way and they 
also fix carbon dioxid more rapidly in the same amount of light than do 
these. Moreover in Convallaria the storage of starch was found to be less, 
the drier the soil. Equally large leaf surfaces containing palisade cells tran- 
spire much more strongly than do those leaves having the structure of shade 
leaves. 

It is evident from these statements that changes of great importance 
must take place in the economy of trees accustomed to shade, when suddenly 
exposed to light, viz., w'hen left standing by removing parts of forests. In 
parks too strong and sudden an exposure to light by the removal of num- 
erous trees not infrequently results in the partial or total death of the 
crowns of the specimens left standing. 

We must turn our attention to still another point. If plantations of 
fruit trees along streets on level land, especially cherries, be examined, many 
cases will be found wih trunks split open on the south or southwest side, 
with the bark torn into tatters and often showing lumps of gum on the 
wounded surfaces. These injuries are very evidently due to frost. The ex- 
planation lies in the fact that the level, cleared lands are exposed in spring 
to extreme temperatures. The February and March sun shining intensely 
on the trunks, and strengthened in its action by the reflection from the soil, 
starts the reserve plant food prematurely and the tissues, being richer in 
water and sugar, at once succumb to the action of the frost. A moister 
atmosphere in the neighborhood of water or wooded areas equalizes the 
temperature and serves as a protection from frost. 

Naturally in regions with greater soil elevations and more noticeable 
differences between valleys and mountains these factors co-operate determi- 
natively and often decisively, but on the plains the forestration is a very 
considerable factor. Cutting considerable forest tracts on wide plains often 
is a source of injury avenged not only on the owner but on the whole neigh- 
borhood, since it increases the chance for damage from late frosts. In this 
connection many small forest tracts, scattered over a large plain, would be 
of use since no considerable distant action from one single large forest may 
be reckoned upon. There is a further advantage to be derived from 
forests, — that of protection against the zvind (windbreak) when there are 
no mountains. 

Just as every bright side has its shadow, forests can exert an injurious 
influence on the adjacent fields. The forest properly located can withhold 
the summer rains, usually coming from the west, from a given field so that 
there will be dry, windless streaks across the fields in its immediate prox- 



137 

imity, — or, on the other hand, the forest may make streaks across the field 
accessible to rains and prevent the rapid drying off of the seeds. In the first 
case, the forest may become a harboring place for injurious insects. It has 
often been observed in the case of dwarf cicades that they begin their de- 
vastation of the fields from the dry edges of the forest. The more severe 
attacks of Puccinia, Ophiobolus and Leptosphaeria herpotriahoides serve as 
examples of the influence of moisture, near the border of the forest, upon 
fungous diseases. Goethe's discoveries^ as to the influence of the place of 
growth upon the canker of fruit trees, caused by Nectria ditissima, must 
be considered. The tendency to disease from canker is favored by an in- 
creased humidity as ofi:ered by higher regions or also by cold valley soils. 
"The trees show in such places a meagre growth and are covered with 
mosses and lichens. Similar conditions are observed also near extensive 
forests, out of which cold, damp air streams even in the summer." 



1 Goethe, Rudolph, Ueber den Krebs der Obstbaume. Berlin 1904. Paul Parey. 



CHAPTER II. 



UNFAVORABLE PHYSICAL CONSTITUTION OF THE SOIL. 



I. LIMITED SOIL MASS. 



Root Curvature. 

For practical agricultural and forestry purposes, the question as to the 
limitation of space in the soil plays a subordinate role when there is no 
scarcity of food stuffs, since disturbances in nutrition, arising from the 
overgrowth and rubbing of roots pressed tightly against one another, or by 
their growth in crevices of rocks, have no agricultural significance. The 
matter is quite dift'erent, however, in gardening and the cultivation of house- 
plants by the plant lover. 

In these circles, however, opinions as to the influence of too small soil 
space on the spreading of the roots are divided. Predominant and also 
clearly expressed on the part of many agricultural chemists is the opinion 
that the mechancial eft'ect on roots, closely pressed on one another and 
tangled by repeated curvature, has no influence on the thriving of the plants. 
They think that in limited soil space only a scarcity of food may ever be 
involved which would make itself felt very quickly and could be corrected 
advantageously by fertilizing. The best proof should lie in the cultivation 
of the so-called "market varieties" by commercial growers in large cities, 
who, conforming to public taste, grow very vigorous specimens of all blos- 
soming plants (Fuchsias, Pelargoniums, Begonias, etc.) in relatively very 
small pots. 

The fact is correct, the explanation, however, inconclusive. 

The restriction of a large root mass in a small space results first in the 
increased production of lateral roots. This may be observed easily in water 
cultures. If one of the large roots reaches the bottom of the glass container 
and its tip is forced to bend around, new lateral roots are produced im- 
mediately. NolF has given special study to this. He found that on the 
bent portions of the main root, the lateral roots were formed only on the con- 



1 Noll, F., Ueber den bestimmenden Einfluss der Wurzelkriimmungen auf 
Enststehung und Anordnung- der Seitenwurzeln. Landwirtsch, Jahrbucher XXIX 
(1900). p. 361. 



139 

vex surface, the concave surface remained free. This is true of both main 
and lateral roots and not only under mechanical influences, but also as a 
result of geotropic and hydrotropic stimuli. Pollock^ has pointed out, in 
this connection, that twisted roots contain more water in the cells of the 
convex side than in those of the concave side. 

Noll ascribes this growth of nev/ lateral roots at the point of curvature 
to a perceptive power of the plant to the formal relations of its own body 
( M or phaesthesia) . This expression may be accepted if by it is understood 
a mechanical transfer of material resulting from the stimulus of curvature 
on the afifected tissues. The process is similar to the one occurring after 
direct injury when the cytoplasm has accumulated in the cells adjacent to the 
wounded surface. Of course laterals are found also on concave parts of 
twisted roots, but, in such cases, the buds of the laterals were present before 
the twisting of the mother root had taken place. 

In trees grown in the open the development of lateral roots on the 
convex side can be of practical advantage, since the plant is thus more firmly 
anchored and extends over a greater area of soil containing food stuffs, 
where otherwise the root branches might not have penetrated. But where 
the whole root ball has only a definitely limited soil space at its disposal, as 
in potted plants, disadvantages arise which must find expression in the pro- 
duction of organic substances. We can perceive these disadvantages at 
once, if we observe more closely a pot said to be "root bound." The greatest 
number of young roots have grown out towards the periphery and been so 
pressed against the porous sides of the flower pot, that many fibres are 
broken oft" when the pot is removed. Part of the root fibres have stuck fast 
like bands or membranes and have died. The latter circumstance is 
especially apparent in palms and Dracaenae, in which the dead roots consist 
only of the stele and the outer bark, which has shivelled up like a papery 
covering. 

The straining of the roots toward the side of the pot may be attributed 
to the need of oxygen. Naturally this demand is less easily satisfied as the 
network of roots fills the ball of earth more closely. To this must be added 
the secretions of the root Itself. Czapek" determined that these secretions 
may be ascertained in moist air as well as in water cultures. In air saturated 
with vapor they are frequently observed as drops on the root hairs, the re- 
sult of a strong internal pressure in the cells. 

Minimum amounts of potassium, calcium, magnesia, sulfuric, hydro- 
chloric and phosphoric acids are eliminated. Potassium phosphate, causing 
the well-known reddening of litmus paper, is somewhat more abundant. 
In regard to acids, Czapek found that the presence of lactic and acetic acids 
could not be proved, but that,on the contrary, formic acid is found not in- 
frequently in its potassium salt as a diffusion product of the living, youngest 



1 Pollock, James, The mechanism of root curvature. Botan. Gaz. Chicago, 
XXIX, 1900. pp. 1 ff. 

- Czapek, Fr. Zur l^ehre von den Wurzelausscheidungen. Jahrb. fiir Vi^iss. 
Bot. 1896. Vol. 29. Part III. 



140 

parts of the roots. Potassium oxalate was eliminated by hyacinth roots. 
Carbon dioxid, however, must be considered primarily and causes the rock 
etchings, as it occurs dissolved either in the water of the root-hair cells or of 
the soil interstices. Monopotassium phosphate and carbon dioxid among 
the root secretions must be especially considered. In pot cultures the latter 
is of especial importance. It is retained in the root balls in great quantities, 
the more thickly matted they are and the wetter they are kept by the grower. 
The production of carbon dioxid is greatly increased by the respiration of 
the soil micro-organisms which in their metabolism decompose the carbo- 
hydrates and other organic substances. For instance Stocklasa^ found 
alcohol, acetic acid and formic acid in forest soil and finally carbon dioxid 
and hydrogen. The hydrogen often unites with oxygen to form water. 
Lack of oxygen and the excess of carbon dioxid kill part of the roots and 
the process is gradually evidenced when plants are grown in small pots, 
even if over-abundant foodstuffs be given them by fertilizing. However, if 
fertile earth alone is used, without subsequent additions of fertilizers, the 
roots, becoming thickly matted on the walls of the pot, do not touch the ball 
of earth actually as they develop on top of older roots. In such cases, they 
cannot further draw from the soil the food materials needed in growth. 

Early investigations by Hellriegel" prove that excessively limited soil 
space in itself limits production. To perform these experiments many 
annual and perennial agricultural plants (barley, peas, buckwheat, clover, 
etc.) were sown in glass containers of different heights in as uniform gar- 
den soil as possible and were grown with an observance of all the precautions 
used in sand and water cultures. In order to prevent any question as to the 
exactness of the results obtained due to a different amount of soluble nutri- 
tive elements control experiments w^ere made with an abundant addition of 
fertilizers, under otherwise similar conditions. The result was, that no 
difference in production whatever was shown in favor of the fertilized 
plants, that those not fertilized must thus have found in the unfertilized 
garden soil all the nutritive substances that they needed for their production. 
An indirect proof lay also in the results of the experiments given by the 
unfertilized plants when compared with one another. The yield showed in 
fact, that clover in the first year had produced about as much dry material 
as the other varieties of plants. This did not prevent the clover, however, 
from producing in the second year on the same soil a second crop and in 
fact a crop two or three times as great, and even in the third year it produced 
as much as in the first year. From this it is evident that the amount of 
nutritive substances could not play a role in any of the experimental pots, 
since they were everywhere present in excess. 

If now, however, the amount of dry substance increased with the size 
of the container, this result could be ascribed only to the influence of the 



1 Stocklasa and Ernest, Ueber den Ursprung, die Menge und die Bedeutung 
des Kohlendioxyds im Boden. Centralbl. f. Bakteriologie etc. Section II, Vol. XIV. 
1905, p. 723. 

2 Hellriegel, Beitrage zu den naturwissenschaftlichen Grundlagen des Acker- 
baues. Braunschweig. Vieweg, 1883. pp. 184-224. 



141 

volume of the soil. The plants under experiment stood in glass cylinders 
of the dimensions and contents given below, received steadily from 30 to 
60 per cent, of the water required by saturation of the soil and resulted 
with clover, as follows : 

Height of the Cylinder. Diameter in the Clear. 

I. 96 to 99 cm. 14 cm. 

II. 65 to 67 cm. 14 cm. 

III. 34 to 35 cm. 14 cm. 

IV. 18.0 cm. 14 cm. 

Earth content. Harvested dry substances, 

Air dry. Absolutely dry. in the years 1872, 1873, 1874. 

19^500 g. 18,600 g. 417-2 g- with 6.92 per cent, pure ash 

13,000 g. 12,400 g. 254.6 g. " 6.97 " " 

6,500 g. 6,200 g. I73-0 g. " 8.08 " " " " 

3,250 g. 3,100 g. 76.8 g. " 8.45 " " " " 

Since, in the containers with a very large soil volume, too great a con- 
solidation, therefore somewhat abnormal conditions for some plants, has 
appeared, because of the sudden addition at first of great amounts of water 
saturating the soil to 60 per cent, of its water capacity, Hellriegel, in his 
harvest tables, explained especially the results for the sizes HI and IV. 
From this it appeared that, with peas, an amount of soil of 

3,100 g. gave on the average, 29.97 in dry substances. 

6,200 g. " " " " 47-94 " " 

For peas, therefore, the proportion of the soil was i :2. 

" " harvest was 1:1.6. 
For beans, therefore, the proportion of the soil was 1.2. 

" " harvest was 1:1.8. 

In 1872, exactly the same proportions in harvest results were found for 
barley as for beans. We omit here the repetition of the figures, since those 
cited show clearly enough that, in two equally wide, but unequally tall ves- 
sels, both containing nutritive substances in excess, and steadily receiving 
the favorable amount of water, the harvest came out as i :i.6 up to 1.8, if 
the amounts of soil bore the proportions of i :2. Thus a strikingly evident 
influence of the soil volume may be confirmed and the question now is, how 
this influence may be explained. 

Hellriegel found that the height of the yield stood in inverse ratio to the 
amount of the mechanical resistance, which opposes the development of the 
root-network of the plants under experiment. 

If commercial growers get apparently opposite results and find that 
the growth in small pots is great and quick, the explanation lies in the fact 
that they use a very rich earth and highly concentrated solutions are present 
in the soil. Comparative measurements showed, however, that the root 
development in rich nutrient solutions is essentially shorter than in weakly 
concentrated ones. Hence the demand of the root fibre is actually smaller. 



142 

However, in the same length of time, the root makes a stronger growth when 
kept under glass, or in hot beds, than where the plants are in the open ; — 
for these glass cases all have bottom heat. Finally, the aerial axis finds itself 
under conditions making possible an especially rapid and abundant develop- 
ment. The atmosphere rich in water vapor and carbon dioxid develops the 
largest individual cells possible with comparatively little transpiration, 
hence, the turgid and significant large size of the foliage. Therefore, in 
garden cultures in small pots, the root is better and earlier formed and 
utilized, so that the injuries due to root curvature and bruising make them- 
selves first felt at a time when the aerial axis has already made a consider- 
able growth. That growers, however, clearly recognize the disadvantage of 
small pots and, when possible, do without them is evident from the so-called 
"feeding cultures" (forcing). In this the specimens are shifted into larger 
pots as the root branches penetrate to the sides of the pot. 

Dwarf-growth (Nanism). 

The dwarf conifers found in trade under the name "Japanese or 
Chinese Trees of Life" show an interesting effect of the influence of a 
limited soil space. The figure on the next page illustrates a living specimen 
which has been classified by the well-known firm J. C. Schmidt (Berlin) as 
Thuja ohtusa and kindly placed at our disposal. The tree, with the pot, is 
86 cm. high in all, — and 60 cm. high above the soil. At its greatest width 
the crown is 80 cm. across. The base of the trunk, divided into several pro- 
truding ridges, has a diameter of 19 cm., the trunk at the height of the 
crown, where the branches appear, one of 12 cm. This healthy specimen, 
with a dense crown, whose age is estimated to be 100 years, cost $87.50. 

In literature, notes may often be found referring to the skill of the 
Japanese and Chinese in growing dwarf specimens of trees, hundreds of 
years old for table-decoration^. 

Our examination of the trunk from a dead tree destroys the halo of 
the miraculous, with which these productions of Japanese and Chinese hor- 
ticulture have been surrounded. A section 8 cm. long and 6 cm. at its 
widest diameter showed most excentric annual rings. The distance of the 
pith from the bark amounted to 1.5 cm. at one side of the trunk and to 6.5 
cm. at the other. Counting with a magnifying glass showed 30 annual rings 
on the wider, but only 15 on the narrower side. On the side favored in growth, 
a great variation in the breadth of the annual rings was noticeable. Four 



1 In an article on "dwarf growth in the veg'etable kingdom,"* Grube quotes a 
report by Sir Geo. Staunton, from "des Grafen McCartney Gesandtschaftsreise nach 
China," Berlin 1798. Staunton snw in Ting-hai, spruces, oaks and orange trees 
none of which were more than 2 feet high and on which fruit had set abundantly. 
At the base of the trunk the soil was covered with layers of stones weathered and 
covered with moss giving the pots the appearance of great age. "Throughout 
China, there is a great liking for these artificial plant dwarfs for we found them, 
as a rule, in every house of any pretention whatever." It is there further related 
that the "liliputian" trees were propagated by binding loam or garden soil around 
different branches. This was kept moist until the branches developed new roots in 
the earth ball; they were then cut off. We still use this process in the layering of 
branches or top shoots and the covering of the cut places with moss. This plan 



143 

zones could be distinguished. Each of these ended with very slender rings, 
the tracheids of which had especially narrow lumina and had become 
browned through resinosis. Otherwise the w^ood was healthy. In its dimen- 
sions the bark corresponds to the section,- — i. e., on the side of the narrower 
rings, it w^as 1.5 mm. thick, on the other side 4 mm. On the narrower side, 
a depression w^as found, in w^hich a scantier development of the wood had 
been equalized by a thicker formation of bark,- — up to 5 mm. There was 
shown here a tendency to loosen the individual bark scales between the flat 
cork layers resembling full cork. 




Fig. 15. Dwarf specimen of Thuja obtusa, 60 cm. high and 80 cm. wide. (Orig.) 

At the base of the trunli may be seen the division of the aerial axis 

into a number of root branches projecting above the pot. 

Thus the statements as to the great age of the trees are seen to be 
erroneous. These cannot be more than some thirty years old and their dwarf 
growth, in our opinion, can be obtained by keeping the plants in the very 



was followed in China, because it had been observed that an artificially produced 
dwarf character is hereditary. When the tendency has become hereditary it is 
strengthened in the new individual by turning down the end bud of the main shoot 
and bending it with wire in another direction. "If it is desired to give the dwarf 
tree the appearance of an old, already half dead tree, the trunk is often covered 
with syrup to attract ants and these, after they have eaten the sweet, immediately 
injure the bark, giving it thereby a brownish, half-weathered appearance." 

Rein** describes the Japanese process which is somewhat different. They call 
the dwarfing or "Nanisation" "Tsukurimono." This expression is not used in the 
new book by Ideta***. According to Rein, the dwarf growth is secured by choosing 



144 

smallest pots until they are root-bound ; then transplanting into a large pot, in 
which the root crown is raised up above the pot in order that the root ball 
may have full benefit from the soil. After the year of transplantation, wide 
annual rings are produced at first, which become narrower as the plant be- 
comes root-bound until the growth has become very slight and the last 
annual ring formed is made up of a few, browned autumn-wood tracheids. 
In this way the stilt-like trunk bases, borne on the freely exposed root 
branches, are produced. The crown is probably kept thick by a light cutting 
back of the tips of the branches, obtaining thereby a greater ramification. 
In the same way the root balls might have been pruned at each transplanting. 
We conclude from the porous places filled with full-cork, which occur 
scattered in the bark, that the trees have been kept wet. At any rate we 
would have no difficulty in growing trees in such decorative dwarf forms 
from the genera Thuja, Thujopsis. Biota, Cupressus and similar ones by 
limiting the soil content. 

A corresponding treatment is recommended here and there for de- 
ciduous trees and plants. In forcing woody blossoming plants it is desirable 
to have for sale small specimens as full of bloom as possible. To attain 
this end, the bushes are planted in small pots, cut back and kept until spring, 
as long as possible, in cool dark cellars in order to retard the growth beyond 
the natural time of awakening. Ice cellars serve best in this connection. 
When vegetation has advanced considerably out of doors the plants are 
brought out. They now find a very dififerent combination of vegetative 
factors for the maturing of their growth. Instead of moist spring air, a 
comparatively slight warmth of the sun and long, cool nights, the plant finds 
dry, bright, long days with little precipitation. As a result the branches re- 
main short and the eyes easily develop blossom buds. 

It will not be out of place to call attention to the fact, that in keeping 
the bushes in warm cellars, an opposite result is obtained, — namely, abso- 
lute unfitness for forcing. The warm, dark place where they are kept pro- 
duces deformed, very premature shoots, which, when brought at last into 
the open air, either dry up or gradually and slowly lengthen to whip-like, 
blossomless wands. The stored-up material has been wasted in the cellar 
in forming the deformed shoots. 



especially small seeds from under- developed plants. These little trees are prun^ed 
and transplanted frequently into as small pots as possible. The cross-section 
described above in the text shows this. Further, the trunk and branches are 
twisted and bent toward the horizontal. It is said that the root ball is cooled. 
Among- varieties of plants used especially in .Tapan for the growth of dwarfs are 
mentioned the tov varieties of Acer p^lmatum, which are budded, "greffe par 
aporoache." Further Pinus massoniana and P. densiflora, Podocarpus Nageia, 
Sciadopytis verticillata. Among fruit trees the Kaki plum. Diospyros Kaki, is 
suitable for this, the Mume-plum. Prunus Mume and Sakura, Prunus Pseudocerasus, 
as well as Amygdalus Persica. Among decorative plants are mentioned Evonymous 
Japonica and the bamboo. 



* "Zwergbildung- im Pflanzenreich" Gartenwelt, 1904, No. 49. 

** Rein, J. J., Japan nach Reisen und Studien. Leipzig-, Engelmann. Vol. II., 
p. 315. 

*** Ideta Arata, Lehrbuch der Pfianzenkrankheiten in Japan. 3rd Ed. Tokio, 
Shokwa.bo, 1903. 



145 

The most frequent occurrence is dzvarfing due to scarcity of zvater. 
Like every other organism, the plant has the abihty of adjusting itself with- 
in wide limits to dififerent conditions. An individual, accustomed from its 
youth up, to a very scanty amount of water, can pull through with half the 
amount of water used by a plant of the same species and variety, which had 
developed with excessive water. Naturally the structure of the whole in- 
dividual is adapted to these conditions. More thorough investigations have 
been made with barley^, which was cultivated with a varied water content 
in the soil (lo, 40, and 60 per cent, of the soil's capacity for absorbing water). 
The most favorable water content for growth might be found possibly be- 
tween 50 and 60 per cent, of saturation. 

In the experiment it was shown that the plant even with only 10 per 
cent, of water had regulated its organization. Little leaf and root substance 
had absolutely been formed, but the proportion between grain and straw 
was normal ; therefore about as much dry substance in the form of grain 
as in the form of straw. With the same amount of food in the soil, the dry 
substance increased as the roots obtained additional water. With too 
much water, i. e., more than 60 per cent, saturation, very little dry substance 
was produced absolutely and this small amount was worthless since the pro- 
portion between straw and grain was changed, — to the detriment of the 
latter. Measurement of the leaves showed that the grains grew longer and 
wider, when water was supplied regularly and more abundantly. These 
larger leaves, found with a greater water supply, are due partly to the in- 
creased number of cells, partly to their greater distention. If the individual 
cells of the upper epidermis are larger, it may be assumed from the very 
beginning, that the respiratory apparatus (the stomatal cells) will share in 
the greater stretching of the upper epidermal cells and will also appear to be 
the more widely separated thereby. Direct measurement confirmed this 
assumption, so that therefore for each square centimetre of a leaf grown 
with abundant water, fewer but larger stomata will be found, than when 
plants are grown with a scarcity of soil water. H. Moller has determined 
by experiments- that plants dwarfed by lack of water (Nanism) are 
structurally different from plants whose dwarfishness is due to a scarcity 
of mineral substances in too weak solutions. In the latter the narrower 
leaves are probably not due to narrower cells, resulting from water scarcity, 
but to a smaller number of cells, since measurements show the same cell 
breadth and the same size of the stomata in plants from a satisfactory nutri- 
ent solution and from an insufficiently concentrated one. These differences 
are easily explained. When the mineral substances are insufficient the cell 
increase will suffer only from water scarcity. The cells are less distended. 
As shown by some of Moller's experiments with Bronius mollis, this nanism 
is not hereditary, since specimens of huge size can be grown from the seed 



1 Sorauer, Einfluss der Was.serzufuhr auf die Ausbildung- der Gerstenpflanze. 
Bot. Zeitung- 1873, p. 145. 

- H. Moller, Beitrage zur Kenntnis der Verzwergung (Nanismus), Landwirt- 
schaftliche Jahrbiicher von ThieL 1883, p. 167. 



146 

of dwarf plants. Yet, with equal vegetative conditions, seed from normal 
plants produces more vigorous specimens than that from dwarfed plants. 

The case of nanism due to scarcity of nutritive substances, which 
Moller studied, is not rare in sandy soils. The lack of nitrogen plays the 
chief part here. This nanism is usually characterized by the fact that, be- 
sides the general reduction, the relations of the separately produced organs 
have been changed. In proportion to the whole growth, the root undergoes 
a greater distention ; but the sex organs sufifer a greater retrogression. The 
number of blossom eyes is very small. Instead of a cluster or a head, there 
is often only a single blossom. Where a greater number of blossoms are 
formed single seeds develop which can germinate. It is easy to understand 
that the leaf-forms are simplified. 

In discussing dwarf growth, the phenomena of bud var'mtion must be 
considered. These have no connection with soil conditions or other external 
vegetative factors. The form of growth up to this time is so changed by 
some impulse or stimulus, acting temporarily or persistently, that the organic 
substance is used up in the form of more numerous, shorter, usually thicker, 
short-leaved branches instead of fewer slender, large-leaved ones, in this 
way producing witches-brooms. In many cases the incitement to such a 
changed direction of growth may be found in parasitic attacks. The fungus 
genus Taphrina (Exoascus) especially irritates the branches of various 
deciduous trees resulting in the formation of witches-brooms (see Volume 
II, page 179). In other cases we find rust fungi or mites of the genus 
Phytoptus. Besides these forms due to parasites, however, some surely 
exist in which other organisms are not active. We find especially in her- 
baceous, quickly growing plants (Campanula, Pelargonium) the occurrence 
of a bud disease (Polycladia) as a correlation-phenomenon. 

In sickness or loss of blossoming branches, small fleshy bunches are 
formed, at times, at the base of the stem, made up of closely set bud-eyes, 
some of which grow out into sickly branches. In diseased thickets growth 
is often exhausted by a continued new formation of short branches, because 
the blossoming axes no longer lengthen, but stop growing and turn yellow. 
In Callima vulgaris, instead of long blossoming branches, we find blossomless 
bunches of twigs, pyramidal in form, which might also be called witches- 
brooms. 

In other cases polycladia and bushy forms are produced by the develop- 
ment of normally formed but still dormant lateral eyes, when the buds of 
the tips have been injured. This takes place when wild growths choke out 
cultivated ones. In conifers, the heart buds grow out and form bushy 
crowns, which are called "rosette-grozvths." The so-called "cozv-bushes" — 
due to injury to beeches, alders, etc., from the grazing of cattle, are similarly 
explained. 

Pure bud variations are numerous. In them the growth in length of 
the individual branches is restricted without any recognizable cause, result- 
ing in a greater and more rapid development of lateral branches. Among 



147 

the actual forms of witches-broom, the tendency at present is to place under 
this head of bud variation the numerous spherical bushes of the spruce 
witches-broom\ The greatest number of examples is furnished by the 
many cultivated plants of our gardens in the so-called globe forms of coni- 
fers and in the dwarf forms of blossoming bushes. In the short-lived sum- 
mer plants (Ageratum, Zinnia, Tagetes, etc.) we find that the dwarf growth 
can become an hereditary peculiarity, persistent in the seed. 

Too Thick Seeding. 

A limitation of the soil space and a struggle for water and nutritive 
substances is always produced by too thick seeding. The struggle of the 
plants with one another for their food appears earliest and sharpest in sandy 
soils. Besides the dwarfing of individual specimens, the weakening of repro- 
duction deserves especial consideration. This becomes evident not only in 
the decrease of the blossoms, but also in the change in their character and 
becomes especially perceptible in horticulture, because staminate blossoms 
are produced predominantly. The unavoidable scarcity of nitrogen is also 
a factor. The greater the amount of nitrogen supplied, the more abundant 
the meristem, rich in cytoplasm. 

Hofifmann- gives the results of many cultural experiments in pots and 
open ground, to determine the influence of too thick seeding for dififerent 
plants. In this, for every lOO pistillate blossoms there developed the follow- 
ing number of staminate ones : — 

With a more seat- 
In With Too Thick Seeding, tered position of 

the plants. 

Lychnis diiirna 233 125 

" 200 77 

" vespertina 150 73 

M ercurialis annua lOO 90 

Rumex Acetosella 152 81 

Spinacia oleracea (average of 

several sowings) 283 76 

In Cannabis his results were contradictory, which may be explained by 
a consideration of Fisch's statement^ that the proportion of the sexes in 
hemp is already determined in the seed, — that, therefore, external in- 
fluences can bring about no further changes. Belhomme maintains that the 
form of the hemp seeds admits of conclusions as to the sex of the future 
plant, since the longer or the more spherical form, as in bird's eggs, indicates 
a staminate or a pistillate individual. 

Since the phenomena appearing with too thick seeding may be traced 
essentially to scarcity of food substances, further examples will be cited 
when the scarcity of nitrogen is discussed. 

1 Tubeuf and Schroter, Naturwissensch. Zeitschr. f. Land- u Forstwirtschaft. 
1905, p. 254. 

2 Hoffmann, H., Ueber Sexualitiit. Bot. Zeituns". 1885, No. 16. 

3 Fisch, Ber. der Deutsch. Bot. Gesellsch. 1887. Vol. 5. Part 3. 



148 
2. UNSUITABLE SOIL STRUCTURE. 



a. Light Soils. 
Disadvantages of Sandy Soils. 

The way in which the individual soil particles are related to one another, 
is termed the structural condition. If the constituents of the soil are simply 
laid one above the other in separate grains we speak of a separate granular 
structure. In soils under cultivation, however, the individual soil particles 
are found united into different kinds of aggregates, called a friable structure. 
While, in the first case, each soil grain has a homogenous constitution, the 
soil grains in the second case are porous and not homogenous, therefore 
can be more easily transformed. The content in soluble salts, the activity 
of the animal world in the soil and the action of plant roots and their se- 
cretions, as well as the physical processes of working the soil, determine the 
formation of a friable structure. The amount of space between the indi- 
vidual grains will vary according to their size and arrangement. Ramann 
calculates the porosity volume of equally large soil particles, according to 
whether the particles are arranged regularly in rows on top of one another 
or between one another, as fluctuating between 47.64 per cent, (greatest 
porosity) and 25.95 P^^ cent, of the whole volume (closest stratification)^. 

While in the friable structure, because of the different individual par- 
ticles, a continuous change in size and arrangement takes place, due to me- 
chanical and chemical influences, in the separate granules, most distinct in 
stony and gravelly soils, the physical relation is more regular and therefore 
more significant. 

We have already spoken of the influence of actual sandy soils and the 
changes which roots can experience when growing in cracks in rocks. The 
injuries to vegetation, which are caused by too loose a structure of stony 
soil at the disposal of the root, seem lessened when the blocks of stone are 
weathered to rubble. Fine, earthy particles are produced, especially when 
the stones are easily decomposed (many granites, Gneiss, Syenite, etc.) af- 
fording the roots more abundant food and firmer support. Next to the great 
possibility of being rapidly heated through, the factor acting most injuriously 
is great dryness, which prevents a decomposition of organic substances lead- 
ing to the formation of humus ; this, under certain circumstances, forms 
moors. Forestry in mountains must take such conditions into account. Sandy 
soils come under consideration for field cultures on the level. As soon as 
these possess greater admixtures of clayey substances (loamy sand) or of 
humus, they form most productive soils and therefore find in this discussion 
no further consideration. Sandy soil is unfavorable for cultivation only 
when the sand is truly quartz sand and is either pure or is present in a very 
high per cent. (70 to 90 per cent.) 



1 Ramann, Bodenkunde, 2nd. Ed., p. 222. Berlin, J. Springer, 1905. 



H9 

In such cases, the slight absorptive capacity should be mentioned first 
of all as a hinderance to cultivation. The diseases caused by scarcity of 
water and food substances are pre-eminently peculiar to sandy soil. The 
more clayey and humus admixtures present, the more the danger disappears, 
in so far as it is not brought about again in another way by the washing 
away of considerable amounts of easily soluble mineral substances. 

Such an erosion takes place much the more quickly when the decom- 
position of organic substances, which occurs easily under the influence of 
warming and aeration, is increased by other conditions. On this account 
one must be especially careful in removing forests and litter. In deep, sandy 
soils, the removal of the litter holding its moisture is disadvantageous since 
the organic substances present are but very little decomposed by atmospheric 
influences and bacteria, and accumulate as raw-humus, which can finally 
give rise to the formation of meadow ore. According to Ramann, in lower 
positions the deposition of raw-humus gradually leads to complete marshi- 
ness, as in the large moors of North Germany, which almost without excep- 
tion have originated from land which at one time was covered by forests. 
The humus is beneficial only when mixed with sand, since the friability of 
the soil and its water content is increased and its capacity for heating re- 
duced. 

This capacity for heating and giving off heat of sandy soils is an 
essentially harmful quality. Pure sand possesses the greatest capacity for 
giving ofif heat and consequently the greatest capacity for becoming wet 
with dew. The process of taking up and giving off heat decreases as the 
sand is finer grained and whiter. Sand of the latter kind, for example, is 
that rich in calcium, while, of colored sands, the ones rich in iron hydroxid 
are very warm and cool ofl: slowly, behaving therefore like sand mixed with 
some clay. 

Associated with the great fluctuations in temperature peculiar to sand 
is the poor capacity for conducting warmth. As a result of difficult equali- 
zation its subsoil has a more even temperature, since it is warmer in winter 
and cooler in summer than under more binding soil coverings. The danger 
from frost is increasedly greater and more injurious. The rapid warming 
in spring days forces vegetation prematurely and the great drop in tem- 
perature at night is injurious, while the plant would be uninjured if it 
started later in a soil containing water and rich in clay. 

The sandy soils of fine constitution and slight coherence present the 
greatest possibilities for injury to crops. The injurious effects of drifting 
sand are shown in the sand dunes. Even if the dunes reduce the severity of 
the sharp sea winds for plants near the coasts, they are nevertheless injurious 
since they advance further and further inland, covering all plants. The 
inability of the land breeze to blow back during the night the sand which 
the sea breeze has swept over the land by day is due to the fact that the land 
breeze is heavily laden with dew and tends to compact the sand again. If 
the danger of being covered with sand threatens and artificial protection is 



150 

too expensive, one must try to bind the movable sand hills by some natural 
method. Sand grasses are here most valuable, since, by the rapid root de- 
velopment of the nodes of the buried stolens, they constantly advance over 
the upper surface and bind it together. Arundo arenaria, L. and Elynius 
arenarius L. are most frequently used. Besides these, Arundo baltica 
Schrad, and Carex arenaria L. should be recommended, and, with sufficient 
moisture, even our quack grasses as well. Among the dicotyledons, Hip- 
pophae rhamnoides, L. is \try good. Depending upon the admixtures in sandy 
soil, experiments may be attempted \vith Salix arenaria L., Lyciuni bar- 
harum, L., Ulex europaeus L. and the lime-loving Genista species. 

No matter whether we are concerned with sandy soil in the interior, 
as in the Mark Brandenburg, Oldenburg and Hanover, or with the sand of 
dunes, the first planting must always take place with the idea of binding the 
sand with low, rapid growing vegetation. Where nature, in the course of 
years, has spread out a' thin vegetative covering, this should be protected by 
every possible means, since, in it, we have a basis which cannot be valued 
highly enough for the ultimate aim of all cultural endeavors, viz., to obtain 
a protective forest. Even if the vegetation is ever so thin, it still restrains 
the sand and makes the planting with young conifers possible. With their 
deeply growing roots they are better satisfied with poor nutritive conditions. 
In the beginning attention should be paid to the production of a bushy 
growth and only later extended inland to the cultivation of tree forms. At 
the sea shore, on all woody plants, a great many branches will always be 
found which have been killed back by the action of the wind. The most 
important cultural method is to leave these dead branches on the plants. 
They break the force of the sea wind and form a natural protection, keeping 
the foliage alive. 

Lowering of the Ground Water Level. 

The building of canals and the regulation of rivers tend to lower the 
water level in sandy soils and act most disasterously on plant growth. In 
contrast to the "soil moisture" of the upper masses, the ground water 
trickles down in the depths, collecting on the impenaous soil layers and 
forming the reserve supply for roots in times of continued drought. 

In regions like the Alpine provinces and the Bavarian plateau, which 
have a high absolute amount of precipitation and smaller evaporation, the 
fluctuations of the ground water level controlled by the annual precipitation 
are of scant significance for vegetation. In regions, however, with scanty 
absolute amounts of precipitation, and great evaporation, where the annual 
fluctuations of the ground water level depend on the amount of evaporation, 
as, for example, on the flat lands of Northern Germany, and where the reg- 
ular slope of the ground water curve indicates a gradual flowing away 
through springs and rivers (see Ramann loc. cit. 275) a lowering of the 
water level by canals and rivers will have the most serious influence. The 
soil dries out very greatly towards the autumn and vegetation becomes de- 



151 

pendent on the water of capillarity. This becomes scantier and scantier, the 
sandier and coarser grained the soil. AA'ithout the supplemental gromid 
water tree growth cannot persist. 

If, in the course of years, the level of the ground water fluctuates a 
half metre in average height the plant growth will adjust itself to the change 
when an equilibrium has been reached. Both the water content and the 
water requirement of plants are correlated with the soil moisture, as Hedg- 
cock's^ comparative cultures in quartz sand, loam, salt soil, humus, etc., 
show. 

Root activity depends also on the water content of soil and plant and 
this activity is by no means passive but, as Sachs- and more especially 
Mohsch^ have shown, is essentially active because the secretions of the roots 
decompose the inorganic and organic substances in the soil. The last named 
investigator calls attention, in this connection, to the circumstance that un- 
injured roots, in contact with a dilute solution of potassium permanganate, 
become covered with a precipitate of brown stone, removing the oxygen 
from the solution. The experiment is unsuccessful with stems and leaves. 
With easily oxidizable bodies, as, for instance, guaiacum, pyrogallic acid and 
humus, the root secretion acts as an oxidizer. A guaiac emulsion is turned 
blue by it. Molisch considered the root secretion to be a self-oxidizer by 
passive molecular oxygen, thereby making the oxygen active and bringing 
about the oxidation of substances which are readily oxidized. In the 
presence of tannic substances (pyrogalHc acid, gallic acid, tannin,) which 
are more easily oxidized than the guaiacum, the blue color does not appear. 
In the same way it is absent in the presence of rapidly oxidized humus sub- 
stances. When absolutely uninjured roots were dipped into dilute cane 
sugar solutions, a reducing sugar became evident after some hours — probably 
this transversion is caused by a root-ferment. Starch paste, put on the 
growing roots of seedlings, did not give the starch reaction after a few hours, 
but w^as turned a reddish violet by iodine. The starch on touching the 
roots had been changed to erythro-dextrin and was soluble, passing over 
into the reducing sugar. 

The root secretions, perceptible on the tips of the root hairs, not only 
impregnate the membranes of the cells but can pass in the form of drops 
into the deeper tissue of the roots when much water is suppUed and trans- 
piration reduced. They can erode minerals with their acids (they turn blue 
litmus red) and decompose organic substances. This action of the roots 
becomes less with increasing dryness. Roots, accustomed to a wet place, 
when brought into a dr}^ one, do not absorb as energetically even after water 
has been supplied, if the plant has been wilted, as if it had not been wilted. 
Hedgocock thinks that the root hairs actually die. 



1 Hedgcock, G. G., The relation of the Water Content of the Soil to certain 
Plants, etc. Botanical Survey of Nebraska. VI. Studies in the Vegetation of the 
State. 1902. 

2 Experimentalphysiologie p. 189. Bot. Zeit. 1860, p. 188. 

3" Molisch, H., Ueber Wurzelausscheidungen und deren Einwirkungen auf 
organische Substanzen. Sitzb. Kais. Akad. d. Wiss., Wien, Section I, October, 1887. 



152 

The production of carbon dioxid forms a measure of the energy pro- 
duced by a root in raising water, boring into the soil and other life-functions. 
Kossowitsch has furnished quantitative determinations on this points He 
found that mustard plants in water cultures assimilated about three times 
as much carbon for the life processes of their roots, as was necessary for 
the formation of the roots themselves. 

The strength of the root activity, especially in lifting water, might de- 
pend also on the differences in temperature between the atmosphere and 
the soil. The greater this difference, the more energetic the work done. 
MacDougal's- experiments in the New York Botanical Gardens prove how 
great such differences may be. He found in June, that the soil temperature 
at a depth of 30 cm. was at times 20°C. lower than that of the air. Naturally 
the water content of the soil here becomes a decisive factor and the differ- 
ences decrease as the soil becomes drier and more accessible to the air. The 
moisture holding capacity and, in sandy soils, the amount of production will 
depend, in the same soil, on its granular structure and will be the greater as 
the sand is finer grained. Livingston and Jensen^ experimented on this 
subject. They cultivated different plant species under similar conditions, in 
soils which contained admixtures of different sized quartz grains in the 
different experimental series. It was shown that the best growth always 
occurred where the quartz sand was very fine. 

By means of the above observations we get an insight into the distur- 
bances which must take place, in the activity of the roots, if the water supply 
of a region is less, because the ground water level has been lowered. An 
old tract of trees survives, because part of the deep growing roots reach 
the ground water level and are able to compensate the loss by evaporation 
of the tree crowns, when the soil water is reduced to a minimum during 
periods of extended dryness. The roots lying in the earth, permeated by the 
ground water, are adapted to these conditions. When these roots are per- 
manently exposed to drought they are destroyed or function feebly. Not 
only the economy of the tree suffers from the insufficient water and food 
supply, but even the soil itself, since, entirely aside from the paralysis of 
bacterial activity, the secreting ability of root hairs and tips affecting the 
decomposition of the soil also ceases. The soil becomes "lean" and the 
trees begin to show dead branches in the periphery of their crowns. Since 
parasites settle on dying parts completing the destruction of the tissues, 
this blight of the tree tops is explained in the majority of cases as a purely 
parasitic disease and treated as such. 



1 Kossowitsch, P., Die quantitative Bestimmung der Kohlensaure, die von 
Pflanzenwurzeln v^^ahrend ihrer Entwicklung ausgeschieden wird. (Russ. Journal f. 
experim. Landwirtschaft, 1904, Vol. V, cit. Centralbl. f. Agrilculturcliemie, 1905, 
Part 6, p. 367). 

2 MacDougal, D., Soil Temperatures and Vegetation. Repr. Monthly Weather 
Review for August 1903, cit. Just, Bot. Jahresb 1903, II, p. 557. 

3 Livingston, B., and Jensen, G., An Experiment on the Relation of Soil Physics 
to Plant Growth. Bot. Gaz. Vol. XXXVIII, cit. Bot. Centralbl. 1904, No. 50, p. 617. 



153 
The Dying of Alders. 

Alders are most sensitive to a lowering of the ground water level and it 
is easy to find diseased tracts of alders near newly cut canals or regulated 
river beds. In the works of the Royal Biological Institution for Agriculture 
and Forestry at Dahlem, near Berlin (1905), AppeP has published a study 
of the death of alders well worth consideration. He found on the dying 
branches a species of the genus Valsa known to attack diseased or dead 
branches, — namely, J^alsa oxystoma — and stated that the fungus is parasitic 
only when the alders become susceptible, owing to abnormal circumstances. 
Drought is the chief determinative factor. Other disturbances in nutrition 
(injury to the roots, girdling, etc.) can also create a predisposition to fungus 
attacks but, if the alders are enabled to make a healthy growth, the disease 
disappears. When alders are found dying on apparently moist, imperme- 
able, ferruginous soils, drought may be considered to be the cause. On such 
soils, the alder spreads it roots only very superficially and in continued dry 
weather there is a very marked scarcity of water in the upper soil layers, 
which at once makes the alder foliage wither and drv^ The beautiful tracts 
of trees in the Tiergarten in Berlin, especially the oaks, unfortunately show 
similar results from surface drought, and to an ever increasing degree. 

Naturally canal and river bed regulations do not always necessarily 
cause the lowering of the ground water level. In the old Botanical Garden 
in Berlin, for example, the building of the subway dried up the water in 
the ponds and as a further result the tree crowns rapidly became blighted. 
In other instances we found that the spread of brick-paving and clay- 
diggings near forest tracts accelerated the death of the alders because the 
deep clay pits had withdrawn water from the forests. 

The dangerous effects of lowering the ground water level often fail to 
impress us sufficiently, since, in some tracts of woodland, the same tree 
species (suffering from blight of the crowns in soils from which the water 
has been removed) thrive in very dry places. Under such circumstances 
the fact that the lack of water in itself does not cause the death of the trees, 
but the abrupt transition from a previously well-watered condition to great 
drought in the deeper layers of soil is overlooked. We may plant all our 
trees in very dry soils and the individuals will adapt themselves to the 
existing vegetative factors and the leaves will become small and coarse, the 
internodes short. But a sudden great change in this condition will have 
most serious results. If, however, such changes are unavoidable, our theory 
gives only one line of action to preserve the plantation, — namely, to plant 
young trees between the old ones. These will adapt themselves to the 
changed vegetative conditions. 

Street Planting. 

The preservation of trees along the streets and small parks is of the 
greatest importance for the hygiene of cities. The greatest injury results 

1 Vorlauflg'e Mitteilung in d. Naturwiss. Zeitschr. f. Land- u. Forstwirtschaft. 
2 Jahrg. 1904. 



154 

from the present methods of street paving which fill the spaces between the 
stones with a binding material, and even at times the asphalt covers the soil 
entirely. The injury to the trees is two- fold; on the one hand, the air is 
cut off, on the other hand watering is insufficient. This affects the older 
trees principally. For young trees, the circle of sod around the tree is 
sufficient, especially if an iron grating laid over it prevents passers-by from 
tramping the soil. We find that old trees die much more quickly when a 
regulation of sidewalks and a lowering of the ground water level is com- 
bined with street paving. In large cities another factor must be added, i. e., 
laying pipes for gas, electricity and sewers. In all this work, the chopping 
off of the larger root branches is unavoidable. 

Therefore, the root space is not only limited by the pipes, and the soil 
dried, but also the trees' organs for the absorption of water are decreased. 
To this cause may be ascribed the gradual break up of old trees as shown 
by the dying branch tips. 

Different varieties of trees suffer in varying degrees and the linden, 
a favorite and most frequently planted species, is among the most sensitive 
of varieties. In it the dryness of the soil, with which is associated also 
dryness of the air, is expressed by a premature defoliation. The large 
leaved linden suffers more quickly than does the smaller leaved variety, and 
it is a well known phenomenon, that, in the summer months, when the in- 
habitants of the city want shade most, the linden and chestnuts often for 
some time have leaves only on the outermost tips of the branches. The 
older leaves, covered with red spider, have dried up and fallen. The city 
adminstration endeavors to overcome this condition by abundantly watering 
the ground about the tree thereby favoring a second leafing out in the late 
summer, which is produced even without artificial watering when the trees 
have lost their leaves prematurely. In this buds are forced to unfold 
which should develop in the following year ; under such conditions a second 
time of blossoming is also often produced (Aesculus, Robinia). 

Many of the shoots artificially produced by this watering do not 
mature sufficiently and are injured by frost. Thus in different years, in the 
middle of the favorable early summer, the twigs die off accompanied by 
fungous infection. The winter, therefore, did not kill these less mature twigs, 
but made them susceptible to fungous attack, thus giving the primary cause 
for later death. This theory also explains the death of the cherry trees along 
the Rhine, which has occupied the attention of investigators during the last 
few years^ A Valsa (J'\ leucostoma) plays a part here as in the case of 
the alders. We will return to this case in the chapter on injuries due to frost. 

Such bad conditions in street planting may be avoided by a choice of 
less sensitive varieties. First of all, the elm should be recommended as 
such ; this has the added advantage of being very resistent to the acid gases 
of smoke. Also oaks and plane trees are used with advantage according 
to the kind of soil present. In broad, airy streets Acer platanoides also 



1 Cf. Deutsche Landwirtschaftl. Presse 1899, Nos. 83, 86, and 1900, No. 18. 



155 

thrives well, but suffers often from honey dew. The Robinise, especially 
the so-called ball acacia, retain their foliage well even in great drought, but 
offer only a little shade and put out their leaves late, usually losing them 
early in autumn. Therefore, when Robinia is planted, arrangements for 
watering should be made, in which drain pipes perhaps Yi metre below the 
pavement are put at the distance from the trunk where the newer roots lie. 
These pipes can be .filled Mdien necessary from hydrants. However, atten- 
tion should be called to the fact that watering through drain pipes can be 
used only in the hot summer months, because otherwise there would be an 
excess of water in the soil with much more disasterous results than those 
due to a scarcity of water. Finally, we think that a sprinkling of the tree 
crown at night should be recommended especially where watering may be 
carried out only through the ground about the tree. 

We must emphatically state that watering by means of water drains 
can be recommended only for light soils with a permeable subsoil. By 
constantly watering heavy soils with a large water content, the soil will be- 
come baked and compacted, resulting in a scarcity of oxygen and an excess 
of carbon dioxid as elsewhere described, which combination will bring about 
the decomposition of the roots. Mangin's^ studies will be cited here as a 
single warning example. He worked especially on the meagre growth of 
trees in city plantingf and found the soils choked to such an extent that the 
carbon dioxid content of the soil air increased from i to 5 and 8 per cent, 
and even to 24 per cent., while the oxygen content fell to 15, 10, 6 and even 
o per cent. As a matter of course all the trees with such an environment will 
die. (Compare "Too deep planting of trees," p. 98.) 

Effect of Drought on Field Products. 

The results of continued scarcity of water, felt most cjuickly in sandy 
soils during great heat, are determined naturally by the time the dry period 
begins. If it sets in in May, as in 1904, i. e., when growth is most rapid and 
the activity which should furnish the material for maturing of fruit is re- 
duced, the effect is most serious. 

In grain, sowing of summer seed suffers most under our cultural con- 
ditions, when planted at the usual time. This is easily understood when we 
consider that winter seeds sown in the autumn can, during the whole 
autumn and the early spring, fully develop their roots and obtain a sufficient 
formation of shoots. They thus utilize the undisturbed activity of their 
lower leaves. In this way the winter seed meets the dry period in a strong 
and well-prepared condition, while summer seed, even where it sprouts 
normally, enters upon the hot, dry period at a much younger developmental 
stage. Accordingly the leaves ripen prematurely, their period of work is 
therefore more limited and even if the plants develop blossoms and the 
ovaries, comparatively little organic matter is present for filling out the 



1 Mangin, L.., Veg-etation und Durchliiftung des Bodens. Annal scienc. agro- 
nom. 2 set-. 1896; cit. Centralbl. f. Agrikulturchemie, 1898, p. 638. 



156 

grain. The endosperm is only scantily filled with starch ; the grains slender 
and light. 

A second injurious effect is the shortness of the straw. This appears 
especially in summer oats, which on light soils have red stalks and grow 
scarcely a foot high, maturing only a few small heads instead of the full 
ones. Barley shows less injury, wheat comes next and finally rye, the most 
resistent. If the dry period makes itself felt as early -as seeding time, the 
plants come up late and unequally. This leads to a double growth, i. e., to 
a very irregular maturing of the grain. At the time of harvest many green 
blades are found among the ripened ones. The former come from the seeds 
which were left on top at the time of sowing, and which at first did not start, 
while those more deeply placed fotmd moisture enough for a speedy germi- 
nation. 

In this, limited local conditions often become effective. Thus, for ex- 
ample, one early crop may have drawn more water from the soil than an- 
other, or a potassium fertiliser is irregularly distributed and keeps the soil 
more moist in the spots where it has accumulated. The whole development 
of the plant is also changed by this. I found under otherwise equal conditions 
that the root shortened when the concentration of the nutrient solution in- 
creased and the plant's need for water became less. This is of great signifi- 
cance in soils imperilled by drought. 

In the cultivation of sugar beets and all vegetables, grown as seedlings 
in small spaces and then planted out in the field, the dryness of the soil 
makes itself felt most of all by preventing the growth of the seedlings since 
no new roots can be formed in dry soil. Next under consideration is the 
drying of the foliage, which stops the development of the beets. Experience 
teaches^ that, as with grain, zvell fertilised fields survive drought better. 
Varieties also show differences in this regard. It has been observed that 
varieties of sugar beets with outspread leaves wilt more easily than do those 
with erect petioles. 

The influence of long continued drought on potatoes shows more in its 
effect on the maturing of the tubers than upon their setting. The tubers 
remain small and ripen prematurely. As a rule, this premature ripening 
of early potatoes is of less consequence economically because they are 
adapted by nature to a shorter vegetative period and because, in the second 
place, they are rapidly consumed. Only the premature ripening of the later 
varieties is disasterous, because the tuber has a small content of starch and 
its keeping quality is much impaired. 

Leguminoseae suffer greatly from continued drought when they are 
grown for fodder. Clover and alfalfa burn out in spots or the second crop 
fails. The most frequent results with fruit trees are the premature ripening 
and poor keeping quality of the fruit and premature defoliation. 



1 Jahresberichte d. Sonderausschusses ftir Pflanzenschutz. Deutsche Landw. 
Ges. 1904. 



157 

Among the special forms of injury which can set in during long con- 
tinued, intensive drought, especially in light soils, one especially deserving 
more thorough discussion is 

The Effect of Drought Upon Germination. 

When the water scarcity occurs after the seed has passed the first 
stages of germination, the results are less serious, if dry seed has been sown 
on open ground than if seed previously soaked has been used. These dis- 
advantages affect the development of the young individual in varying de- 
grees dependent upon the kind of seed and the age of the seedlings when the 
drought takes place. According to Will's repeated experiments^ with seeds 
of monocotyledons and dicotyledons, the seeds of the former seem in general 
to be somewhat more resistent. The cereals without glumes (wheat and 
rye) are very little sensitive to a period of drought, if it occurs during 
germination. Barley and oats, however, are injured more easily, and the 
horse-tooth maize has very little power of resistance. Saussure- found 
that maize, beans, poppies and garden campion are very susceptible to 
drought during germination. Nowoczek'' in his experiments repeatedly in- 
terrupted the supply of water, until the power of germination of the seeds 
was quite lost, and found that the seeds of grains resist the changing con- 
ditions of moisture and drought better than rape, flax, clover and peas, 
which lose their germinating power earlier, but even after a period of 
drought these seeds can be revived. Experiments on the Gramineae showed 
that after each drought period the fibrous roots, already formed, died, and 
the outermost leaves dried up, but that, when water was again supplied, 
new adventitious roots were formed from the first node (see Vol. I, p. 102) 
and the last leaves developed further. This statement applies especially to 
oats and to a greater or less extent to barley, wheat and maize. 

It should be considered as universally well-established that soaked and 
then carefully dried seeds, when put again into water take it up more quickly 
than do air dry, non-soaked seeds of the same size. Such seeds in fact 
germinate a few days earlier. 

Tautphous* and Ehrhardt^ made experiments giving results which 
were expected at the start,- — viz., that plants suffer so much the more, the 
further germination has advanced; i.e., the more developed the plumule is 
when the drought begins, the greater the damage. Will found the seed of 
peas in part especially sensitive to dr3dng out. The testa was broken by 
many small cracks in most cases reaching into the inner layers. With re- 
peated soaking, the palisade layer was broken into unequal pieces, the 

1 Will, Ueber den Einfluss des Einquellens und Wiederaustrocknens auf die 
Entwicklungsfahigkeit der Samen. sowie iiber den Gebrauchswert "ausgewach- 
sener" Samen als Saatgut. Landwirtsch. A^ersuchsstationen XXVIII, Parts I and 2 
(1882). 

2 Annales des sciences nat. Bot. 1S27. Janv. 

3 Ueber die Widerstandsfahigkeit junger Keimlinge. Wissensch. prakt. Unter- 
suchungen etc. von P. Haberlandt, Vol. I, p. 122; cit. Biedermann's Centralbl. I, p. 
344. 1876. 

4 Freiherr von Tautphous. Die Keimung der Samen bei verschiedener Be- 
schafCenheit derselben. Miinchen 1876; cit. Bot. .Jahresber. 1S76, p. 882. 

5 Deutsche landw. Presse, .Tahrg. VIII, No. 76; cit. von Will, 



158 

testa became slimy and shortly decomposition set in, affecting the cotyle- 
dons, which hindered the development of the seedlings. The production of 
these cracks is due to the increase in volume of the seeds, when soaked, to 
more than lOO per cent.^ This produces a pressure on the testa and dis- 
tends it, making it porous. This porosity can lead with dr}-ing even to' 
rupturing. Through these cracks in the testa, the embryo, when moistened 
a second time, gets much more oxygen for the food-reserve already be-, 
ginning to decompose, and also large Cjuantities of water are more c}uickly 
absorbed. Further, the dissolved organic materials are transferred more 
easily osmotically. These may act unfavorably on further development. 
A testa slowly and equally distended, remaining uninjured, will there- 
fore probably more completely utilize the reserve substances of the cotyle- 
dons and perhaps indeed force the fluids into the tissue of the cotyledons and 
the dissolved reserves into the embryo by the turgidity produced by soak- 
ing. We cannot enter here more closely into the enzymes occurring in ger- 
mination and their action, but refer in this connection to the works of 
Newcombe- and Griiss^. 

From these experimental results it can be safely asserted that the use 
of seeds, which have been soaked until germination has started and then 
dried off, should be avoided. I am also of the opinion that soaked seed is 
to be used sparingly every time especially in dry regions. In the first place, 
in dry regions, the conditions already brought about artificially by drying 
soaked seeds can be repeated most easily in nature by continued heat and 
drought and act much more injuriously than if the seed, in such a condition, 
lay ungerminated in the soil. In the second place the plants become ac- 
customed from the beginning to an excessive water supply. The tissue be- 
comes more porous, richer in water and, requiring more moisture, dries up 
much earlier with the occurrence of great periods of drought than if the 
plants had developed with a scanty supply of water. The evaporation in the 
former condition is greater than in the latter. On this account, growers 
often follow the rule that for vegetable plants developing rapidly (cucum- 
bers, beans and cabbages) watering must not be discontinued, if the plants 
have had abundant water when young. I have often found that plants from 
soaked seeds are less thrifty than plants grown from the same seed which 
had not been soaked, but which depended upon the natural moisture of the 
soil. 

Treatment of Tree Seeds. 

If the germination of tree seeds is interrupted by drought, the results 
are very disasterous. This is felt most in planting trees whose seeds retain 
their germinative power only a short time. Nobbe* found that the seeds of 



1 Nolibe, Handbuch, p. 122 

- Newcombe, F. C, Cellulose-Enzymes. Annals of Botany 1899, No. 49; cit. 
Bot. Jahresb. 1899, II, p. 179. 

3 Griiss, J., Beitrage zur Enzymologie. Berlin 1899. Festschr. f. Schwendener, 
Ueber Zucker- und Stiirkebildung: in Gerste und Malz, III u. IV. Wochenschr. f. 
Brauerei 1897, 1898. 

4 Dobner-Nobbe, Botanik f. Forstmanner. 4tli. Ed., 1882, p. 382. 



159 

willows lose their power of germination in 5 to 6 days after they have been 
blown from the parent tree. The seeds of poplars and elms are also proved 
to be very short lived. Acorns and beech nuts, as a rule, are capable of 
germination only until the following spring. On an average, ash, maple and 
fir come under the same head. On the other hand, a large percentage of 
spruce and pine seeds germinate after 3 to 5 years ; however, the seedlings 
are apt to be less vigorous. The maturing of the seed and the care of it 
after it has been gathered are important factors. For example, Nobbe 
found that seeds of Pinus silvestris, which had stood in closed glasses in a 
living room, germinated after 5 years to about 30 per cent, and after 7 years, 
to 12 per cent. In fact, even after 10 to 11 years, individual seeds were 
still found capable of germinating. Under the same conditions, seed of 
Trifolhim pratense, after 12 years, germinated to 10 per cent., Pisum sati- 
vum, 47 per cent, after 10 years and in one experiment, Spergula arvensis 
25 per cent., another year 67 per cent. It is stated that cedars and Italian 
pines (Pifion) have germinated after 30 years\ It is advisable to sow fine 
seeded conifers soon after ripening. The time of planting, whether summer, 
autumn or spring, is a question of practical importance. The summer is 
the most difficult season because the moisture fluctuates to a great extent in 
the soil ; therefore, with trees whose seed must be sowed immediately, as 
willows and poplars, propagation by cuttings will obviate this difficulty. 
Autumn sowing is much better and necessary with oaks, chestnuts, hazel 
nuts, etc. It is recommended for very hard shelled seeds like those of 
Crataegus, Prunus, Ilex, Sorbus, Rosa, Cornus, Berberis, Ribes, Carpinus, 
Staphylea, Clematis, etc. The last named kinds often do not germinate for 
2 to 3 years, especially in sandy soils. Spring sowing is best because the 
danger of winter and all injuries due to animals are eliminated. In order 
not to lose the time between the autumn and spring, the seeds are placed in 
layers between sand, which is kept damp. This process is called 
stratification. 

The importation of seeds of prized decorative trees from their native 
countries has become a large business. It is important to know the loss of 
germinating power during transportation. Count von Schwerin- in the 
German Dendrological Society has called attention to the fact that maple 
varieties cannot withstand any long transportation, so that, for years, not 
one of the maple seeds brought from the Himalayas had germinated. Also, 
the seed bed should not be broken up too soon, since many seeds retain their 
vitality for a long time in the soil. Thus, for example, Chamaecyparis Laic- 
soniana often lies 4 years in the soil, especially in dr)^ years. For years, in 
the trade in Magnolia hypoleuca from Japan, either no seeds germinated or so 
few that the costs of transportation were not paid. The seeds dried during 
the journey. Y^ry encouraging results have been obtained recently by leav- 
ing these seeds in their fruit and packing them in powdered charcoal. 



1 and - Ueber das Keimen von Geholzsamen. Der Handelsg-artner 1905, No. 14. 



i6o 

To the statement made heretofore that the seed of Acer retains its 
germinating power until the following spring, the qualifying statement must 
be added, that maple seeds of the Campestre group (Acer obtusatum, A. 
Italum, etc.), as a rule, germinate only in the second year. Only occasional 
seedlings may be found after the first year. In many botanical gardens, how- 
ever, trees of the Campestre series are said to furnish seeds usually germinat- 
ing early. The explanation of this is that in seeding in such places, the first 
seedlings are used for propagation. From this it may be concluded that the 
peculiarity of producing seeds, which germinate promptly, may be made 
constant by selection. This point of growing the earliest germinated seed- 
lings separately as seed bearers, when making large seedlings, might be 
recommended for the consideration of plant breeders. 

Blasting in Grains and Legumes. 

Under these circumstances the seeds do not mature since the plants 
do not have enough water. Such a condition of great drought is most often 
found on soils of a verv^ porous structure where evaporation is very great 
and the capillary movement of water from the subsoil is slight. 

Yet great scarcity of water will not always produce a blasting of the 
blossoms. This depends essentially, as Hellriegel's experiments with grains 
show, on the development of the plant when the water scarcity makes itself 
felt. If, following the experiments^, a grain plant has had only a scanty 
amount of water at its disposal, beginning at the time of its germination, 
it reaches maturity in a period of the same length, or perhaps somewhat 
longer, yet the whole growth is weak. The proportion of the harvested 
grains to the dry substance, however, is always normal ; i.e., approximately 
half of the dry substance is harvested in the form of grain. As in all 
vegetative conditions, there is here also a minimum ; if the water supply is 
kept below this, no product worth naming takes place. 

If great scarcity of water occurs immediately after germination begins, 
the grains remain alive for a long time (in the experiment up to six weeks) 
and later develop vigorously, when the water is supplied in abundance. A 
period of drought appears to be still less injurious if the grains are still in 
the milk stage, i. e., have reached their normal size, but have not 
finished their inner development and become hard. The work of the plant, 
which now forms no new dry substance, consists in transposing the sub- 
stances produced in the leaves to the storage organs, the seeds. 

In all periods of growth between sowing and ripening, a longer scarcity 
of water acts more injuriously the younger the plant is at the beginning of 
the drought. When the long drought sets in while the seeds are sprouting 
vigorously, the setback resulting therefrom cannot be overcome. The results 
of continued drought are the more severe, the more water the plant has had 
in its youth. If a plant has grown luxuriantly with abundant soil, up to the 



1 Hellriegel, Beitriige zu den naturwissenschaftl. Grundlagen des Ackerbaues. 
Braunschweig. Vieweg 1883, pp. 589 to 620. 



i6i 

setting of the bloom, and then receives a check from a long drought, the 
grain is not set ; a greater or less extensive failure of the harvest takes place, 
which we may call the blasting of the grain. Ritzema Bos'^ experiments 
with "Maartegerst," or winter barley sown in March, are very interesting. 
A sowing was made on a field where autumn sown winter barley was frozen 
out. Only a few of the autumn sown plants came through the winter and 
produced stalks during the summer so that the same field produced autumn 
and March sown barley. The plants from the March seeding suffered dur- 
ing the hot summer from blasting, while the plants of the autumn sowing, 
scattered among them, bore a full harvest of grain. With us, besides grain, 
peas suffer most. Naturally in other plants as well, a failure of the seed 
harvest can take place, due to the blasting of the blossoming parts. 

Thread Formation in the Potato (Filositas). 

In this disease ("mules" — of the French) the eyes are deformed; from 
them grow slender, thread-like stems as thick as medium sized yarn. Not 
infrequently the eyes of tubers comparatively rich in starch did not sprout 
at all, or if they did, the sprouts were weak ; they are unable to break 
through even a shallow soil covering. The tubers decay usually with the 
appearance of dry rot, yet the disease has occurred extensively only where 
the soils, being easily heated, have to withstand long droughts. 

Fig. i6 shows the basal part of a cutting grown in a water culture 
from a potato affected by Filositas ; the proportions of the stem, leaves and 
tuber correspond to the natural size and it is seen that the stems actually 
are only as thick as a strong thread of yarn. The stolons {st.) are also 
more delicate and have formed tubercles {k) , some of which have lengthen- 
ed at the tip and grown out to green sprouts (h) or developed scale-like 
green leaflets {d). 

The cutting here reproduced came from an experimental culture, the 
results of which are given in precise figures in the second edition of this 
manual and lead to the conclusion that in the thread disease of the potato 
we have before us conditions of premature ripeninq zvhlch had become 
hereditary. Reports from the localities where the disease has occurred, 
especially from the March f eld near Vienna", of the cultural methods fol- 
lowed there, substantiate this theory. The potatoes, which were of the 
earliest varieties, were forced artificially and planted as soon after as possi- 
ble. Sandy soils on the March f eld near Vienna, lime soil near Poitiers", 
had a small water capacity and heated rapidly, consequently with the in- 
creasing summer temperature and the superficial position in the upper soil 
layers the growth of the aerial axes stopped at once. Tubers are formed 
about this time, but they do not mature, they are filled with starch so that 
they can be marketed ver}^ earl)' and command high prices. 



1 Zeitschr. f. Pflanzenkrankh, 1894. p. 94. 

- Altvatter, Das Marchfeld und seine Bewiisserung\ Oesterr. laiidw. Wochenbl. 
1875. No. 51. 

3 Journal d' Agriculture pratique; cit. Biedermann's Centralbl. f. Agrikultur- 
chemie, 1873, No. 10 und Annalen d. Landwirtsch., 1873, Wochenbl., No. 16. 



1 62 



When young tubers are checked, ripen prematurely and are harvested, 
the eyes have not developed normally. Shoots developing from these eyes 
must naturally be weak. If such tubers are used the following year as seed 



Fig. 16. The basal portion of a cutting grown in water from a potato tuber with 
the filament disease (natural size). (Orig.) 

for similar cultivation, these phenomena of weakness must gradually m- 
crease and result finally in the growth of thread-like stems only. According- 
ly the disease is the result of a continued unwise cultural method ; viz., an 



i63 



admissible shortening of the vegetative period of growth. To overcome this 
difficulty the seed must be changed since the method of cultivation will not 
permit the return to normal seeding. 

DiAPHYsis (Growing Out) of the Potato. 
In summers with little rainfall, as, for example, in 1904, one of the 
most frequent complaints was that the potatoes remained small or when ap- 
proximately normal size, showed an uncommonly large formation of sec- 
ondary tubers (" Kindelhildung" ) . In Fig. 17 is illustrated one of the most 
bizarre forms, which shows two kinds of diaphysis (growing out), viz., the 
actual "formation of secondary tubers" and "water ends." The stem end 
of the tuber (at the left side in the drawing) shows two daughter tubers 





'^k ' ■ W 




V ^ 




Fig. 



17. Proliflcated potato; at the left the beg'inning- of complete lateral tubers; 
at the right, subsequent elongation of the tip end (water ends). (Orig.) 



growing on either side at about the same relative position like the arms of 
an armchair. Toward the tip we find the daughter tubers becoming smaller 
and smaller, until near the conical end of the tuber (right side of the 
picture) they are recognizable only as small hemispherical processes. 

This malformation is caused by Prolepsis, i. e., a premature or hurried 
development of the eyes. The explanation of this phenomenon is easily 
found. After prolonged foliage development the imderground eyes of the 
potato plant develop tubers which store the already manufactured starch. 
The drier the summer, the more quickly the tuber ripens, since, with the 
regular enlargement and increase of its cells, the starch grains enlarge and 
the cell walls thicken. The cells (except the youngest about the eyes) grad- 
ually lose the ability to increase in size to any extent. 

If now, after prolonged drought and advanced ripening, a considerable 
amount of water is forced up into the tuber, this abundant absorption of 



164 

water increases the cell pressure, especially in the young eye cells with their 
still elastic walls, so that the eye begins to grow. Young shoots sprout from 
these eyes ultimately reaching the upper surface of the soil. This more un- 
usual condition occurs only after continued wet weather. As a rule, only 
passing periods of rain force the water into the tubers, an efifect lasting but 
a short time ; then the sprout remains short and thickens to the secondary 
tuber (Kindel). 

The cork layer (the skin, smooth in young tubers) shows very clearly 
how the cells of the ripening tubers lose their elasticity. When the tubers 
are very ripe the skin becomes rough in most varieties of potato, especially 
red ones. At first the cells of the cork layer are closely connected with one 
another but, with the increasing pressure of the swelling parenchyma, the 
cells are forced apart, tearing the skin. Under these tears new cork cells 
are formed. This splitting of the skin is greater or less with different 
varieties. The more split a tuber of an otherwise smooth-skinned variety 
is, the riper it is and the richer in starch. 

Diaphysis of the tubers in many cases has a bad influence in that the 
quantity of starch which may be regarded as influenced by the soil, is de- 
posited in a less available form than in normal development. Together with 
the large tubers a great many small ones are formed, which are less mature 
and therefore poorer in starch. According to the investigations of Kiihn^ 
and Weidner-, the tubers already present do not become poorer in starch 
when the secondary tubers are formed. The starch of the secondary tubers 
does not come from the original tuber, but directly from the leaves. Only in 
plants, whose foliage is dead, does a suddenly renewed supply of water pro- 
duce secondary tubers at the expense of the starch content of the older ones. 
Both old and young tubers have only the starch content of the healthy 
tuber, which has not grown out. 

So-called "water ends" are nothing but the result of a renewed growth 
of the apical parts of the tuber excited by a subsequent supply of water. 
These are thereby lengthened into a conical form and are filled with new 
starch (see the right side of Fig. 17). The starch filling is just as scanty 
as in the real secondarj^ tuber, "Kindel." 

Formation of Tubers A^'ithout Foliage. 

If tubers, at the time they would sprout naturally, are not put in the 
earth, but are kept in a dry, poorly lighted room until the next period of 
harvesting, a number of small tubers will sometimes begin growth. These 
stand either close against the mother tuber or hang from short stolons, 
which have developed from the eyes. While, with a timely supply of water 
and light, these eyes would have grown into leaved, green sprouts, in the 
dry, dark store-room, the sprouting eye has developed into a thread-like 
runner (stolon) beset with scales instead of leaves, the tip of which has 
thickened into a tuber. 



1 Zeitschr. d. landw. Centralver. der Prov. Sachsen 1868, p. 322. 

2 Annalen des Mecklenb. patriot. Ver. 1868, No. 39. 



i65 

Aerial Potato Tubers. 

When tubers are not planted deeply, nor hilled up, the plant remains 
green, while the root is liable to be greatly injured by drought or animals. 
If subsequent rains cause the weakened roots to function sufficiently to keep 
the aerial axes alive, small, colored tubers are developed on them from the 
lateral eyes. This process is possible also under different conditions, yet 
the root must be diseased and able to convey only very small amounts of 
water from the soil to the leafy stems. If cuttings are taken from the older 
parts of the stem, they can be forced to form tubers in the leaf axils. 

Premature Ripening of Fruits. 

In years of continued drought, as, for example, 1904, complaints be- 
come most numerous that fruit does not keep. Summer fruit indeed ripens 
more quickly and can be brought to market one to two weeks earlier, but the 
flavor leaves much to be desired. Winter fruit remains smaller, as a rule, 
is less juicy and well-flavored and decays more quickly, or it needs a much 
longer time in storage in order to become fit to sell. The former may be 
observed with light soils, the latter has often been found^ when, with heavy 
soil, rains occur after a period of drought, causing a further growth of the 
fruit which, until then, had been retarded by a scarcity of water. 

The condition here pictured is explained in the discussion of the fact 
that the quality and keeping qualities of the fruit depend upon two factors. 
First of all, each fruit must have sufficient time for the penetration of the 
water and food substances necessary for its maturity; this takes place at 
the time of swelling. Then the oxidation processes of ripening set in grad- 
ually, in which the reserve material, stored in the form of starch, is used up 
in respiration. The longer time the fruit has to store up the material sup- 
plied by the leaves, the better provided it is for the process of ripening and 
the better are the keeping qualities. If this process is interrupted ahead of 
time by drought, the processes of ripening, the conversion of starch into 
sugar, find comparatively little material present. In normal summer 
weather, i. e., alternate sunshine and rain, the fruit during the process of 
ripening also takes up mineral elements besides water, as Pfeiffer and I have 
proved. An absolute increase in mineral substances takes place shortly 
before complete ripening. This naturally appears relatively small in com- 
parison v/ith the greater increase in organic substances. With a continued 
scarcity of water this increase does not take place and the fruits quickly 
use up the scanty materials. The acid store is scanty, the formation of 
sugar still less, which accounts for the insipid taste and the poor keeping 
qualities. 

In winter fruit, processes of ripening are completed only in storage. 
But in all other respects the same point of view holds good. If the weather 
during the summer is favorable for the absorbing of large amounts of re- 



1 Monatsschrift fiir Pomologie unci praktischen Obstbau von Oberdieck und 
Lukas, 1863, p. 272. 



i66 

Serve substances, the fruit is well prepared for storage and keeps sound a 
long time. If the reserve substances are scanty, the fruit rapidly spoils. In 
seasons after a long period of drought, which has practically stopped the 
development of the fruit, if a time of continued cool, dry weather comes, 
the fruit may start its growth again and renew its life processes. If the 
fruit must be harvested in the autumn, it is put into storage in a compara- 
tively immature condition and thus needs more time to become ripe. These 
are the cases (on the whole less frequent) in which the fruit must lie dis- 
proportionately long in storage and does not become mellow, but remains 
tough. 

Rusty Plums. 

Fox red discoloration of plums setting in some weeks before the normal 
time of ripening is a phenomenon of premature ripening. The fruit is still 
absolutel}^ hard and, on an average, about half as large as that normally 
ripened. As a rule, the rusty plums fall prematurely. The phenomenon 
occurs only in continued hot, dry periods and is found especially on sandy 
soils. This discoloration occurs at different times for dift"erent varie- 
ties and is similar to the premature coloration, which takes place in wormy 
or otherwise injured fruit. It should be emphasized that the dry locality it- 
self is not the cause of the rustiness of the fruit, but it is due to a scarcity 
of soil water succeeding a period of normal precipitation. Trees whose 
water supply is scant, adjust themselves to conditions by dropping the fruit, 
which they cannot develop, shortly after blossoming. The disease only ap- 
pears on those trees which have held their fruit until summer under normal 
moisture conditions, which are then followed by a long, dry period. An 
abundant supply of water must be provided to overcome this, and should 
not be too long delayed, else not only the rusty fruit but often all the fruit, 
will fall. 

Further Phenomena of Premature Ripening. 

As a matter of course, the results of continued soil dryness after a nor- 
mal spring moisture are observable in all kinds of fruit. The dropping of 
leaves and fruit is of frequent occurrence. The scanty maturing of the 
organs remaining on the plant is a less common phenomenon. This produces 
also poor keeping qualities in stored fruits and potatoes and small grains in 
the cereals. We will return later to the discussion of other cases, when we 
consider the results of unusual dryness of air. 

Mealiness of Fruit. 

Especially in hot summers on sandy soils it has been observed that 
fruit, especially early varieties, does not become juicy and crisp, but is 
tought, poor in sap, insipid rather than aromatic in taste, and when put 
under pressure, makes a mealy paste. In cooler years and in other localities 
even the same varieties do not become mealy, but change at once a firm con- 
dition to a liquid, winey, doughy or a decomposed condition. 



167 

I know of no special investigations of the case at hand. On this account it 
can be stated only hypothetically that the mealiness of the fruit depends upon 
a definite act in the ripening process, which has been directed into other chan- 
nels because of the scarcity of water. This change in direction might not be as- 
sociated with the connection of the fruit and the tree, but may set in late in 
the development of the fruit, about at the time when the intercellular sub- 
stances generally dissolve. In normal ripening of fruit, after passing the 
stage of great sweetness, in which the fruit is already "mellowing," i. e., the 
cells of its flesh are easily separated from one another, there occur at the 
expense of the sugar first an alcohohc and finally an acetic acid fermen- 
tation. The fruit becomes winey and doughy with a constantly advancing 
oxidation or browning. According to PYemy^, a part of the alcohol thus 
formed is combined with the fruit acids to form the ethers, which condition 
the flavor of the fruit. A cool temperature prevents the rapid oxidation of 
the sugar. The supply of water from the branch to the fruit, becoming less 
with ripening, explains the fact that, in great summer heat, the fruit develops 
with extraordinary rapidity and in this gives oft' carbon dioxid and water 
abundantly. In fruit, however, the flesh is poorer in water and is very 
easily warmed through; the reduction of the intercellular substances, which 
we reckon among the pectines, cannot take place in the usual way. A. 
Mayer- considers the pectines as condensation-products of Galactose and 
the pentoses, Arahanose, and calls attention to the peculiar fact that they 
are jelly-like because of a special enzyme and are hydrolized by another to 
the pentoses. It may indeed be assumed that these processes are changed 
quantitatively and qualitatively when the fruit becomes mealy. This is indi- 
cated by the circumstance that in mealy fruit a firm connection always exists 
between the outer skin and the flesh of the fruit, while in the normal winey- 
doughy condition the outer skin can be raised easily from the flesh, i. e., the 
intercellular substance is dissolved. The insipid taste of mealy fruit is ex- 
plained by the scanty content of acid and the quick destruction of the sugar. 

When establishing the theory that an excess of warmth can cause a 
relative lack of organic acids in fruit, attention must be called again to the 
fact that the acids formed in the leaves during the night are in great part 
used up again during the following day. This process of oxidation will also 
take place in green fruit and it is indeed conceivable that in the long, hot 
summer days, this is so intensive that a large part of the acids already pro- 
duced disappears. Under such circumstances no vinous fermentation takes 
place. 

The fact that I was able artificially to produce the mealy process in 
apples favors the theory that the mealiness of fruit appears with the scarcity 
of water in the cells and a pasty decomposition of the cellular substance, if 
the conditions necessary for a vinous fermentation are not present. Fruit 
of various sorts was packed in layers in dry sand after ripening normally 



1 Compt. rend. LVIII, p. 656. 

2 Agrikulturchemie, 5th. Ed. Vol. I, p. 141. Heidelberg- 1901. 



i6g 

on the trees and was kept from autumn until the next summer in a cool, 
light cellar^ in order to let the fruit mature as slowly as possible. In this it 
was proved that some fruit with an absolute uninjured wax coating was still 
sound in August, but absolutely insipid in taste and of a mealy consistency ^ 

Bitter Pit. 

In the flesh of fruit, especially of apples, brown, tough, scattered spots 
are produced, which sometimes taste bitter. If these are found just beneath 
the skin they become noticeable as somewhat depressed tough places, which, 
at first paler in color, finally become brown. The phenomenon is most fre- 
quent with porous soil in dry years, such as 1904. The firm fleshed varieties 
suffer less. Although a fungus Spilocaea pomi Fr. is given by some in- 
vestigators as the cause, I still would like to consider the phenomenon as the 
result of a too rapid maturing in individual cell groups in the flesh. In each 
fruit the tissue of the flesh seems unequally filled with reserve substances. 
If premature dryness of the soil prevents the accumulation of the proper 
amount of organic material for the complete maturity of the fruit, different 
tissues will remain especially poor in contents and actually complete their life 



1 In mealy fruits, as well as in those normally juicy, the state of ripeness is 
characterized by the appearance of peculiar substance groups becoming visible 
immediately after the sections have been put in undiluted g-lycerin. 

The adjacent figure shows a cell from an apple (Gloria mundi) when the section 
had been placed immediately in g-lycerin. The delicate plasmatic primordial utricle 
which had been contracted into folds is partially omitted in the drawing-. The 
content is pushed together more or less. Also the very large vacuole at once notice- 
able in most cells, usually lying in one corner (which I would like to call an acid 
vacuole), is omitted in the illustration so that the substances appearing with the 
glycerin reaction may be more clearly apparent. Emphasis should be laid upon 
the fact that all cells do not show this response. The outer flesh of ripe apples, 
pears and peaches reacts especially well. The investigations indicate that a 
substance closely related to sugar is present in the cells in various transitional 
forms. This substance is found between isolated larger vacuoles or the numerous 
very small ones; it might be imbedded in the cytoplasm or be free in the cell sap, 
either as separate cloudy drops or in rectilinear masses which, from their appear- 
ance, may be dough-like in consistency. Often they are found in more strongly 
refractive and solid forms as tuberous, warty, irreg-ular growths. This most solid 
state appears also in the form of very small, sandy grains imbedded in the cell wall, 
attention to which is first called when they swell up to drops or (by forming 
vacuoles) to small bubbles in the g-lycerin. All three forms have a capacity for 
swelling in glycerin. When observed under water, the drops become indistinct and 
disappear, but in extracted apple juice they remain visible and may be distinguished 
from the different vacuoles. The radiating middle structure of the figure shows the 
most marked results of the swelling-, while the doughy condition of the substance is 
indicated by the shaded surface with curved outlines lying below this. The sur- 
roundings represent the part of the cytoplasmic sack, which lies in the same plane 
and which encloses the grains of coloring- matter and two vacuoles. 

The process of swelling- is the same in the three masses described above, but 
occurs in different intensities. It appears most rapidly and furthest developed in the 
drop form and decreases the firmer the substance becomes. With the addition of 
water the drops disappear first, in their place there remains at times a finely ground 
residue at the edge of the cytoplasm; somewhat later the doughy masses become 
invisible and the dividing line formed through the cytoplasm becomes circular. The 
polyp forms become slowly transparent; the warty masses gray grained and 
cloudy without dissolving entirely in one day. If, at the beginning of the entrance 
of water, cloudy balls, generally lying along the walls imbedded between the 
vacuoles, are observed, there is frequently noticed a swelling of different groups of 
cell contents beginning at the inside, which increases up to the formation of vac- 
uoles. A similar phenomenon is found with glycerin where the process sets in more 
slowly and the changed conditions are retained longer. By this process of swelling 
of the substances imbedded in the cloudy drops, the inner part of these appears 
at times filled by one or more vacuoles in such a way that an actual cloudy mass 
occurs only as a slender ring enclosing the vacuoles. This becomes more and more 



169 

cycle so much the more quickly. The beginnings of the disease must be 
sought in a rather early stage of the fruit's development. I often found in 
diseased cell groups, recognizable by browned and corked membranes, many 
grains deposited on the cell wall. These slowly colored blue with iodine 
and therefore must be spoken of as starch. Some of them showed a warped 
seam which remained whitish. Further, a splitting of the browned tissue is 
observed often in the tough fleshed early apple, varieties which are most 
inclined to become specked. These splits are explained by the fact that when 



transparent in water until it can no longer be recognized. No actual dissolving- of 
the substance has been observed. If fresh sections are laid first in water, cloudy 
drops do not appear, from which it may be concluded that the substance is taken 
up by the water. Indeed, in several cases, it was observed (in Reinettes) that if 
the drops had disappeared after a rapid temporary action of the water there was 
left a fine grained residue. With the addition of glycerin the solid grains either 
form drops or separate filament-like pouches. Per- 
haps it is only these grains which, imbedded in the 
drops and the remaining, above-mentioned forms 
claimed to be different aggregate conditions of some 
ground substance, swell up to polyp-like radiations. It 
is seen especially in the drops which are enlarged to 
a thick-walled vesicle by a vacuole that only some 
places may be elongated like pouches or chains of 
beads which in individual cases can reach the wall 
layer and thus transverse the cell as knotted bands. 
With the continued slow swelling in glycerin the 
figures change constantly whereby the substance, 
which becomes more and more doughy, more weakly 
refractive and stringy, shows an attempt to return to 
the drop form. Either some of the chief arms of the 
above represented polyp-figure take up more and 
more substance and become broad bands which finally 
draw together into spherical drops, or separate beads 
of the chain show a stronger growth with a constant 
increase in size and decrease in refractive power, 
whereby the smaller spherical links of the chain and 
the thread-Ike substance possibly connecting them 
becomes more slender, finally tearing apart and be- 
coming drawn into the larger drops. In most pro- 
nounced cases these drops were recognizable after 96 
hours, but later could no longer be found nor pro- 
duced again by reagents. 

The reason that I place the substance mentioned 
in the list of sugars, or between sugars and ferments, 
is their occurrence in the same cells, which contain 
large, strongly refractive drops capable of being 
drawn together by glycerin, or separated by alcohol and 
showing a copper reaction into which it seems to me 

pass over the small, above-mentioned drop forms. The large syrup drops which 
may be drawn together in certain parts of the cytoplasmic sac by glycerin and 
which gradually disappear again, may be partially fixed by the use of the potassium 
bichromat since a persistent brown -grained precipitate is formed. In pears I found 
this phenomenon after the action of dilute sulfuric acid on the glycerin preparation 
in which the walls of the stone cells became the color of wine. Ferric chlorid gives 
no special color reaction. If a piece of caustic potash is put in the glycerin prepar- 
ation the syrup balls color an intense yellow and the remaining cell content a 
lighter yellow. Chemically pure grape sugar behaves similarly but, dissolved in 
pure water, it gives only a weakly yellow liquid. The addition of calcium chlorid 
or calcium nitrate will hold the drops in form somewhat longer. They then retain 
their strong refractive power from 2 to 4 days. With the use of silver nitrate a 
brown grained precipitate is produced in many syrup balls, which consists either of 
many very small grain bodies or less numerous larger tuber-like ones. A part of 
the drops disappear without giving any precipitate. 

It seems to me that we are concerned here with an extremely easily changed 
substance, easily soluble in water and alcohol, but less soluble in glycerin, which 
occurs in the same cell in different transitional stages, thus howing different re- 
actions Even exposure to the air brings about a change, since an apple, which 
shows a quantity of drops on its freshly cut surface, does not show any drops on 
this same cut surface after a few hours when acted upon by glycerin, and these may 
only be found again deeper in the tissue. 




Fig. 18. Parenchyma cell 
from the flesh of a ripe 
apple after treatment with 
undiluted glycerin. (Orig.) 



170 

the fruit was attacked by the disease, while the cork layers were swelling, 
the specked tissue had already lost its elasticity. 

The dying of single tissue groups of this kind as the result of an in- 
sufficient storage of reserve substances will take place so much the more 
easily as the deposition of starch is made more difficult by the one-sided in- 
creased nitrogen fertilization. In fact, practical fruit growers have also 
observed that this specking is especially abundant, if the trees have been 
excessively fertilized with sprouted m.alt, hornshavings, etc. 

Wortmann^ substantiates our theory in regard to the non-parasitic 
character of the specks and of their occurrence with a scarcity of water. 
He ascribes the appearance of the dead cork cell groups to an excess of acid 
which is brought about by the concentration of the cell sap of the fruit as 
a result of unreplaced water loss. The absolute acid content decreases with 
the ripening of the fruit, but the relative acid content becomes increased 
with scarcity of water in the cells. Wortmann concludes from his investi- 
-gations of the epidermis that the larger fruits evaporate more than the 
smaller ones and the specked varieties (reddish Reinette, Goldgunderling, 
King of Pippins, Landsberger, green Stettiner, Danziger) evaporate more 
than do the varieties not inclined to specks. He found a greater thickening 
of the outer walls of the epidermis in the non-specked varieties, the peeled 
specimens of which evaporated more than did peeled specked apples, li 
the fruit of non-specked varieties was pricked with a needle and laid in acid 
or alkaline solutions (potassium, tartarate, limewater) specks were pro- 
duced which could not be distinguished from natural ones. 

The phenomenon of the so-called "fly specks" should not be confused 
with this. Very fine little black points united into groups are found on the 
apple peel, which appear to the naked eye like a cloudy bloom and under the 
microscope look like accumulations of fly specks. Fungi, especially 
Leptothyrium pomi Mntg. and Fr. and Phyllachora Pomigena (Schw.) 
Sacc. are given as the causes. Often actual insect secretions are found in 
which fungi grow. Since the skin under the "fly-specks" does not seem to 
have been injured in any way, rubbing with a damp cloth is enough to make 
the fruit again fit for sale. Another phenomenon, often called specking, is 
the "rusting of the peel." This term comes from the change in color oi 
the outer skin. During the process of sivelling, the skin gets stellate or den- 
tritically-branched tears, which are closed by the formation of cork. 

Stoniness of Pears and Lithiasis. 

When pears are grown on poor soils, in dry years the flesh is solid, but 
grates between the teeth when eaten, in wet years the flesh is tender and does 
not grate between the teeth. This grating is due to the extraordinarily large 
amount of stone granules formed in the years of drought. Practical workers 
often maintain the theory that the formation of stone cells in pears is the 
direct result of great drought. 

1 Wortmann, Jul., Ueber die sog. Stippen der Aepfel. Landwirtsch. Jahrbiicher 
1892, Parts 3 and 4. 



in 



Investigations of young fruit show, however, that in each variety of 
pear in normal development aggregations of coarse-walled schlerenchymatous 
cells are always present unequally distributed. These stone cells are in fact 
an anatomical characteristic dififerentiating pears and apples\ Therefore, it 
is not the occurrence of the stone cells but only the greater thickness of the 
walls already formed which is the result of the drought. In many varieties 
they remain relatively thin-walled. To this should be added that their con- 
nection witji the surrounding tissue is tougher and closer in dry years. 

In the so-called stoniness of pears, only the increased wall-thickening- 
of the normally deposited schlerenchy- 
ma cell centres is concerned and there- 
fore no increase of the elements, while 
we find in Lithiasis an accumulation 
of stone cell elements produced subse- 
quently by cell increase. These finally 
may also extend over the surface of 
the fruit and then form light brown 
circular specks, either equally distrib- 
uted or clustered on the sunny side or 
even map-like etchings due to the run- 
ning together of the specks (Fig. 19), 
the upper surface of which shows a 
crumbly construction. Not infrequently 
the same varieties of pear suffer 
also from Fusicladium (see Vol. II). 
Nevertheless, the Lithiasis specks may 
be easily distinguished from the smooth, 
usually blackened, fungous specks, be- 
cause of their crumbly constitution and 
the raised edges of the wound. 

So far as observations have shown 
as yet, only certain varieties suffer 
from Lithiasis. Many, in fact, form 
predominantly roundish specks, while 
in others usually zigzag gapping cracks 
are produced. Stone masses are not 
always depressed, often they occur on the upper surface as pale cork-colored 
cushions. 

An entirely normal construction may be found in the healthy parts of 
the pear attacked by the stone disease ; i. e., underneath the small celled, not 




Fig-. 19. Pear diseased with 
Lithiasis. (Orig.) 



1 Turpin, Memoire sur la difference qu'offrent les tissus cellulaires de la pomme 
et de la poire etc. Paris. Compt. rend. 1838, T, pp. 711 ff. 

~ The substance, of which the stratified thickened walls of the stone cells con- 
sist, has received the name of glycodrupose from Erdmann*. He used this name 
because he thought that the chemical composition of these cells is the same as that 
of the tissue of stones of plums and cherries (Drupaceae). The substance, decom- 
posed by moderately concentrated hydrochloric acid, gives half its weight in grape 
sugar in solution. The half remaining undissolved is called drupose; when boiled 



1^2 

very thick-walled, colorless epidermis (Fig. 20 e) lie three or four layers of 
usually tangential ly elongated or cubical parenchyma cells (/>) which are 
richer in cytoplasm than the deeper lying tissues and contain chlorophyll, 
but no starch. The starch is found to appear gradually first in the inner 
flesh and its grains usually increase in size toward the core. Underneath 
the outer cell layers, rich in chlorophyll, the deposition of the stone cell 
centres begins {st). These form groups of a few cells in the normal flesh; 
in the coarse fleshed fruit they are separated only by small intermediary 
areas of delicate parenchyma (-/'). From the periphery toward the in- 
terior of the fruit, the stone cell groups become more scarce and the sur- 
rounding parenchyma assumes a stellate arrangement. 

In the first stages of the disease, we find in fruit, which is always green 
and hard, that, underneath the uninjured and colorless epidermis, individual 
cells contain no chloroplasts, but have a brown, strongly refractive cell con- 
tent, which is massed together in lumps. The number of these browned 
cells gradually increases and ruptures the outer skin. Beneath the ruptured 
place which, by the drying and crumbling decomposition of the tissues forms 
a depression {gr), a brown- walled dying tissue {hr) is found in the 
midst of the flesh, which later may rupture and form cracks. Often in 
these cracks, and always in the open peripheral pits {gr), may be found a 
colorless slender mycelium which is a subsequent infection and may hasten 
the decomposition of the tissues. 

A most striking phenomenon is the fact that when the pit has been 
formed the flesh tissues no longer die and closed masses of newly formed 
schlerenchymatic tissue begin to push out like cushions with a radial struc- 
ture (/). These cushions of stone cells force the dead bark {t) tissue out 
and off. 

In cross-section the individual elements of the stone cell cushions are 
square or rhomboid, and lie almost unbrokenly upon one another. Even in 



with nitric acid and washed with water, ammonia and alcohol this leaves behind 
a yellowish white celk^lose. Erdmann concludes from his investigations that the 
substance of the stone cells may be produced from a carbohydrate by the loss of 
water and nitrogen from starch or gum, while in the normal process of ripening, 
water must be taken up for the formation of the sugar. 

The theory that the formation of sugar and of cellulose are most closely connected 
is given expression by DeVries**. He says that usually an accumulation of grape 
sugar is found in those young cells which later strongly thicken their walls. For 
example, the bast fibres of clover as well as fibres of the inner fibrous sheath of the 
vascular bundles, which appear to be very thick walled in a mature condition, are 
rich in grape sugar in their younger, still thin walled stage, while the surrounding 
tissue is poor in sugar or lacks it entirely. DeVries found the same conditions in 
the young bast fibres of potato and maize. Even in the hairs, which are thick- 
walled later, an accumulation of sugar takes place before the thickening of the 
walls, thus, for example, in the hairs of young clover leaves, in whose parenchyma, 
however, no sugar could be proved. In the same way, according to DeVries, sugar 
can not i)e found in the root parenchyma of this same plant, while in the young root 
hairs it occurs abundantly. The possible transversion of cellulose to dextrin and 
sugar by the action of dilute sulfuric acid after heating is well-known. With this 
the recent investigations on the Hemicelluloses; mannen, galactan and araban, 
should be compared. 



* Liebig's Annalen, Vol. 138, p. 101; cit. im Jahresbericht f. Agrikulturchemie 
1866, p. 99. 

** Wachstumsgeschichte der Zuckerriibe, in den Landw. Jahrb. 1879, p. 438. 



173 

early stages they color a bright yellow with Anilin sulph. and when oldest 
will dissolve easily in sulfuric acid without any observable precipitation 
of gypsum crystals. While the normal stone cells usually remain yellow 




Cross-section of a stone cell cushion from a pear diseased with Lithiasis. (Orig-.) 

Explanation in text. 



174 

from the effect of sine iodid of chlorid, the elements of the schlerenchyma 
cushions, which were formed later, turn blue after some time, either 
throughout or in the innermost lamellae of the walls. 

The growth of these schlerenchyma cushions takes place in a meriste- 
matic layer (w) formed underneath the dead bark and appears at first as if 
it would develop into a flat cork layer, cutting off the centre of the diseased 
tissue, as may be observed in the Fusicladium cushions. This, however, is 
not the case. The meristematic layer is active as long as the fruit is green 
and growing. Toward the periphery it forms new thin-w^alled bark cells 
(usually in small numbers) which again are gradually attacked by bacteria 
and fungi, while on its inner side, toward the (usually seedless) core, the 
thick-walled elements of the stone cell cushions are increased. 

The radial arrangement of the cell rows in these is explained by the 
tension of the tissues which the swelling of the unripe fruit causes. If, in 
this, the new formation of stone cells is greater than the distension of the 
parenchymatous tissue of the fruit flesh, the stone cells are pushed out like 
cushions. As a rule, however, both processes keep step and finally, by the 
death of the pathogenic meristem itself and the breaking of the connection 
between the outermost stone cells, is produced the crumbly constitution of 
the stone spots. 

It is a matter of course that fruit attacked by Lithiasis is unfit for 
consumption. 

Since this phenomenon is not found in all varieties, and not ever}^ year 
even in the same varieties, but is a destructive factor only on dry soil in dry 
years, the supposition, that the stock used in grafting influences the problem, 
seems probable. Weakly growing stock which cannot take up sufficient 
amounts of water from a dry' soil for a rapidly growing top, because of its 
small root area, will favor this stony condition. If, on this account, the dis- 
ease should occur repeatedly in the case of dwarf trees on light ground, an 
attempt should be made to graft pears on the most rapidly growing varieties 
of quince. When standard trees are in question, an attempt to overcome the 
difficulty should be made by renewing the soil, fertilizing the sub-soil and 
watering abundantly ; in obstinate cases, by means of renewal of the top by 
pruning after fertilization. Some method of forcing the fruit to swell as 
rapidly as possible might best protect it from an excessive formation of 
stone cells. 

Varieties of Fruit Suitable for Dry Soils. 

The guiding idea of our manual is that many diseases of cultivated 
plants may be prevented by a more careful consideration of the relation 
between the character and habits of the plant and its environment. In 
accordance with this plan in treating diseases favored by drought, we men- 
tion a number of well-known varieties suitable for dry soils^. 



1 Oberdieck, Deutschlands beste Obstsorten, Leipzig, Voigt. 1881. L. indicates 
that the variety i.s recommended to the agriculturist. Str. suitable for planting 
along streets. The name of the month after that of the variety indicates the time of 
complete ripening. 



175 

Apples: Summer Rose, End of July. L. Str., Scarlet Pearmain, Au- 
tumn. L. Str., Landsberg, Autumn. L. Str., Dantziger, Autumn. L., King 
of Pippins, Winter. L. Str., Orleans, Winter. Str. (For the agriculturalist 
where the soil is better). Yellow Bell flower. Winter. L. Str., Alant, L., 
Deutscher Gold Pepping*, Winter. L. (must be left on the tree until the 
middle or end of October), Kassler, keeps from winter until summer. L. 
Str., Purpurroter Cousinet*, winter till summer. 

Pears for dry soils: Hannoversche Jakobsbirne*, end of July. L. Str., 
Clapp Favorite. August. L., Archduke, August. L., Yat, beginning of Sep- 
tember. L. Str., Kuhfuss*, beginning of September. L. Str., Treyve, Sep- 
tember. Autumn Melting (Downing), end of September. L. Str., Bosc, end 
of October. L., Marie Louise, beginning of November. L. Str., Mecheln, 
December. Madam Korte*, January. Kemper, cooking pear for the whole 
winter. L. Str. 

Cherris, as is well-known, prefer a well drained, dry soil; on the other 
hand, plums, on the average, flourish best in a moist, heavy soil and also 
they bear sweeter fruit. It is desirable to know a number of varieties re- 
quiring less water. Biondeck, beginning of August ; early Apricot, middle 
of August; Lawson, end of August; Bunter Perdrigon, end of August; 
Berlepsch, beginning of September; Altham, beginning of September; Jerus- 
alem, beginning of Septembr; Anna Spath, middle of September; German 
prune, end of September. As a street tree, the plum is not very desirable 
because of its habit of growth. 

As varieties which grow well on dry, light soils in the climate along 
the coast, should be mentioned^ : i. Apples: Landsberg, Purpurroter Cousi- 
net*, Oldenburg. Geflammter Kardinal*, Bauman ; the Prinz (Downing) 
is especially suitable for the provinces along the Baltic and the North Sea. 
2. Pears: Yat Bosc, Red Bergamot, Summer Doyenne. 3. Plums: House 
Plum. 4. Cherries: The common sour cherry. 

Stunting. 

Since almost everywhere in nature similar effects are obtained by 
different means, a limited soil space may be only one cause of dwarf growth ; 
another is the lack of available nutriment due to either a scanty supplying of 
raw soil solution to the roots or to the decrease of organic reserve nutriment. 
This latter case we will have to consider again later in the "PIncement Grin," 
I. e., in the pruning of leaves to prevent the sprouting of the buds found in 
their axils and in the production of dwarf seedlings by cutting off the 
cotyledons which are rich in nutrition. 

In nanism, however, caused by soil physically unfit because of too great 
porosity, water scarcity alone must be considered. Given a soil rich in mineral 
or organic food substances, the size of the plant depends upon the distension 



* Name of variety given in the German original, not reported in the United 
States of America. 

1 From a written communication of Mr. Klitzing- (owner of a nursery) in 
Ludwigslust. 



176 

of the individual cells, due to the turgor produced by the water from the 
roots, and the conclusion is at once reached, that a scanty supply of water 
during the time of growth must produce small dwarf specimens. Each 
excursion through sandy regions, in which a damp subsoil is either lacking 
or lies very deep, furnishes examples enough for this fact. I have published 
detailed measurements concerning the shortening of cells due to a scarcity 
of water\ MoUer- furnished experimental proof of dwarfing due to scar- 
city of other food substances with an excess of water and also confirms the 
principle that in slightly concentrated nutrient solutions the root increases 
relatively in size. Mobius^ has arrived at the same result in his comparative 
cultures with Xanthium in sand and loamy soil. He found the roots and 
stalks of plants grown in sand branched more than those of plants grown in 
loamy soil, while the leaves were more slender and the glandular hairs 
fewer in number. On the other hand, in plants grown on loam the content 
of calcium oxalate crystals seemed smaller. The thorns were smaller on 
sandy soil, but the walls of the lignified cells seemed considerably thicker. 

Comparative studies of the influence of dry or wet localities were made 
by Duval-Jouve"*. These proved that in dry. hot places, a formation of the 
hard, bast bundles is especially favored, but is retarded in shady, wet posi- 
tions. Volken's observations"' on Polygonum amphibiunt in the forms grown 
in sand, heath and water, are very thorough. In the sand form the circum- 
ference of the stem is smaller, at the expense of the central air canal ; the 
bark cells are more heavily thickened, while between the bark and the 
phloem, a rather broad ring of uncommonly thick mechanical cells is en- 
closed. A closed wood cylinder is formed, the vascular system in which is 
almost 2 to 3 times as strongly developed as in the water-grown stem ; in 
the latter, the absence of thick-walled elements and the occurrence of large 
air holes facilitate floating. The petioles of the water form, which have no 
mechanical reinforcement, may become six times as long as in the land form, 
the midribs of which are strengthened by strong collenchyma cords. The 
palisade cells are more strongly developed in the water plants, but these 
lack, on the other hand, the strongly developed bristles on the upper sur- 
face and here also the somewhat larger epidermal cells which in the land 
form contain a slimy content, explained by Volkens as a water reservoir in 
times of great drought. In the well-known Rose of Jericho (Anastatica 
hierochuntica), that plant of the desert which closes together like a head 
when dry, the inclination of the branches toward each other arises from the 
fact that the wood cells on the different sides of each branch possess a 
different capacity for swelling longitudinally, which goes hand in hand with 
an unecjual lignification. 

1 Sorauer, Bot; Zeit. 1873. 

2 Moller, Beitrag-e zur Kenntnis d. Verzwerg-ung. Landw. Jahrb. 1893, p. 167. 

3 Mobius, M., Ueber den Einfluss des Bodens auf die Struktur von Xanthium 
spinosum usw. Ber. d. Deutsch. Bot. Ges. 190.'j, Vol. XXII, Part 10. 

4 Duval-Jouve, Anordnung der Gewebe im Blatte der Graser. Bot. Jahresb. v. 
Just 1875, p. 432. 

5 Volkens, Beziehungen zwischen Standort und anatomischem Bau der Vegeta- 
tionsorgane. Jahrb. d. Kgl. Bot. Gartens zu Berlin. Vol. Ill, 1884, p. 46; cit. Bot. 
Centralbl. 1884, No. 46. 



i;7 

From the beginning one must note that every Hmited supply of nutri- 
ment which leads to nanism must express itself mostly in the amount of 
additional growth, i. e., in the formation of the secondary tissues. An ana- 
tomical proof of this has been furnished by Gauchery®, who cites cases 
when the cambium has formed anew only a few rows of cells. Often he 
could no longer determine any meristematic zone whatever between phloem 
and xylem; therefore, the original cambium must have passed over at once 
into permanent tissue as the result of deficient nutrition. 

In the plants which are forced to grow in sandy or stony soil, often 
with a lack of water, a form of hyperplasia^ (arrested developments) 
appears. It is not so much the number of the cell elements which seems 
to be decreased, as their size. Thus specimens are formed which we would 
like to call "stunted plants." By this is understood woody plants, the growth 
of which is not retarded to dwarfing but which, by the striking shortening 
of their axial organs, show a repressed, knarly habit of growth. 

In this habit of growth the very evident, increased spiral twisting of the 
woody elements of the trunk counts as a typical characteristic. The finest 
examples are seen in Syringa and Crataegus. We can explain the production 
of the increased spiral twisting if we think of the direction of the woody 
cells as the diagonal of the parallelogram of two forces. 

At the apex of each elongating axis there is, on the one hand, an efifec- 
tive striving toward growth in length in which the elongation of the pith 
body becomes a decisive factor of swelling; on the other hand, the general 
enlargement of the young cells acts also as the cause of the radial enlarge- 
ment of the trunk. In considering a very young wood cell in the cambial 
layer, stretching longitudinally, we see that, as the growth in length predomi- 
nates over the growth in thickness, it is relatively difficult to divert the cell 
from its longitudinal growth. However, as the abundantly formed young 
wood cells, during elongation, are pressed outward by the growth in thick- 
ness of the medullary cylinder in the direction of the radius of the trunk, 
proportionately just so much the sharper will be their spiral twisting. On 
this account we find long slender shoots with a slight spiral twisting in 
plants on moist nutrient soil, and on sandy soils poor in water, or with other 
checks to growth in length, plants having short axes with strong twistings. 

Confirmation of the hypothesis is found in the "enforced twisting" to 
be mentioned later. The more the stems are distended like barrels, the 
sharper is the spiral twisting of the cords of the leaf spur. 

We mention this point because the occurrence of such strongly twisted 
stunted plants is valuable as a symptom in judging the soil conditions. 

Pilosis. 

Plants grown on dry soil soon have a hairy appearance, even if no more 
hairs are formed than on specimens of the same variety growing in damp 

6 Gaucherv, Recherches sur le nanisme vegetal. Ann. sc. nat. Bot. 1899. VIII. 
ser., t. IX. 

1 Kiister, E., Patholog-ische Pflanzenanatomie, Jena 1903, p. 21. Here abundant 
bibliographical citations. 



1/8 

places. If a definite number of hairs are formed on a leaf, these are closer 
together in a given small area, because the epidermal cells separating them 
are shorter. This partially explains why alpine plants appear to be less 
pubescent when grown on plains. These plants grow more luxuriantly, the 
dimensions of their organs become larger and the hairs are separated further 
from one another. But, in fact, even in dry locaUties, an increased hair for- 
mation takes place. Thus Moquin-Tandon^ cites observations by Lianeus, 
that the Lady's Thumb (Polygonum Fersicaria L.j seems very smooth at 
the edge of bodies of water, but beset with hairs in dry places. Our field 
thyme (Thymus Serpyllum L.) loses its glaucous surface at the sea shore 
and acquires a short, hairy covering. Our Turk's cap lily (Lilhim Maria- 
gon L.) when cultivated for some time in gardens is glaucous, but becomes 
pubescent again, like the wild plant, when grown on poorer soil, etc. Such 
phenomena may be observed also in garden plants which, self-sown, grow 
on sandy places in the fields. 

An unusual hair growth takes place, further, in many parts of plants 
when they no longer develop normally. According to Moquin-Tandon, the 
stamens of the triandrous bindweed are covered with thick wooly hairs. 
The stamens of several kinds of Mullen (Verbascum) behave similarly if 
the anthers become deformed. The peduncles of the smoke tree (Rhus 
Cotinus) are almost without hairs before blossoming and if they bear seed. 
If, on the other hand, the fruit does not mature, the stems of the sterile 
blossoms grow longer and numerous, long, violet colored hairs appear on 
them. The last-mentioned formation of hair does not belong among the 
phenomena connected with drought, but should be considered as a process 
of correlation. The water and nutritive substances, which should be utilized 
in the maturing of the anthers or seeds, are used in a greater measure for 
the benefit of other parts of organs, when the sexual organs are destroyed. 
Possibly the phenomena recently observed in parthenogenesis belong in part 
here, where the micropyle is stopped up as the result of the hair-like elon- 
gated cells of the style tissue or of the integuments-. 

Also, we find in the root system that pubescence varies according to 
the place where the root is kept. In the same varieties, the whole system 
can develop into the form of long, slender, whip-like, scantily branched, 
bare, or almost bare roots, if the root axis dips into water or into porous 
sand saturated with water. The root branches become shorter, more 
knarled, branched and pubescent, the drier the soil is in general ; — the more, 
therefore, that the root is obliged to depend only on the moist air of the soil 
interstices. In air which is absolutely dry, the roots (according to Per- 
secke^), do not develop any more hairs. If the roots are exposed to moist 
air, the young tips, just behind the growing apex, become very hairy, be- 
cause almost every epidermal cell has pushed out into a hair. 

1 Pflanzen-Teratologie, translated by Schauer, 1842, p. 61. 

2 "Winkler, H., Ueber Parthenog-enesis bei Wikstroemia. Ber. d, D. Bot. Ges., 
Jahrg-. 1904, Vol. XXII, p. 573. 

3 Persecke, Ueber die Formveranderung- der Wurzel in Erde und Wasser. 
Inauguraldissertation, Leipzig- 1877. 



1/9 

In the aerial parts of plants, which are accustomed to dry air, the de- 
gree of humidity must be strikingly low if the formation of hair is to be 
greatly stimulated as C. Kraus^ states when writing of potato sprouts. In 
very moist air potato sprouts from the same variety are hairless, or have 
only a few shortish hairs. Therefore, in aerial organs, it is the influence of 
moist air in contrast to dry air which prevents pubescence. In roots, de- 
pending mostly on water, the same effect is obtained by a continued supply 
of water just as the influence of moist air favors pubescence. 

An extreme formation of hair on aerial and subterranean axes is there- 
fore the result of causes acting in the same way ; the usual necessary amount 
of water is withheld from the plants at the stage in which they are develop- 
ing. 

In explaining the fact that greater dryness of the environment favors 
the formation of hairs, Kraus and Mer- have cited the phenomenon that the 
organ's growth in length is modified or arrested with the formation of 
hairs. Both investigators are of the opinion that the material saved by the 
arrested elongation of the cells of the axis, is utilized for the formation of 
hairs. Besides the examples of Rhus, etc., cited above, Heckel's" observa- 
tions support the theory that a scanty formation of other organs goes hand 
in hand with a very abundant development of hairs. Meckel found speci- 
mens of Lilium Martagon L. and Genista aspalatholdes Lam. with an un- 
usual hair covering together with a reduction of the blossoming parts. 
Kraus emphasizes the fact that, with the decrease of growth in length, an 
increase in turgor takes place transversely in the whole organ (as we have 
assumed in the development of the pith of stunted plants) which extends to 
the epidermal cells and excites these to the pushing out of hairs. Vesque'', 
like Mer and Kraus, states that increased transpiration favors hair for- 
mation. 

Attacks of parasitic animals often excite the epidermal cells to an 
enormous, fine growth of hair, for example, such as mites which injure the 
young leaves with their mandibles and thus produce the so-called felty dis- 
ease. These hair formations are described under galls. In the older my- 
cology, such hair felts, produced by the sucking stimulus of mites, are de- 
scribed as fungi (Erineum Pers. Taphrina Fr., Phyllerium Fr.). 

LiGNIFICATION OF RoOTS. 

The lignification of tuberous roots is due to the return to the original 
prosenchymatous woody condition of cells in the vascular bundles which, 
under cultivation, have become parenchymatous. The carrot, for example, 
which serves us as food, descends from a plant whose root consists of a 



1 Kraus, Beobachtungen liber Haarbildungcn, zuniirhst an Kai-toffelkeimen. 
Flora 1876, p. 153. 

2 Mer, Recherches experimentales sur les conditions de developpement des polls 
radicaux. Compt. rend. LXXXVIII (1879), p. 665. 

" Hecliel, Du pilosisme deformant dans quelques vegetaux. Compt. rend. t. XCI, 
1880, p. 348. 

■t Sur les causes et sur les limites des variations de structure des vegetaux. 
Cit. Bot. Centralbl. 1884. No. 22, p. 259. 



i8o 

strong, hard, wood body with a thui, tender bark. The cells of the wood 
tissue, like all the other wood cells, are thick-walled, spindle-shaped and 
wedged between one another. In the cultivated root, instead of these wood 
cells, thin-walled, short cells are present, ending almost bluntly against one 
another and even the ducts which lie in scattered groups between the par- 
enchymatous cells are but little lignified. The latex tubes already formed in 
the bark, when spiral porous ducts are produced in the wood body, have 
broadened like all the cells of the bark. Instead of the starch which, in the 
wild carrot, fills out the whole bark tissue, occurring here and there in the 
wood body also and increasing to 70 per cent, of the dry weight, sugar has 
been formed usually in good table carrots so that only traces of starch may 
be found. The better the variety, the less the starch content as in the 
Dutch pale yellow and the Duwicker carrot. Gradual transitions are found 
back toward the wild plant in other cultural varieties used as fodder, such 
as the Altringham carrot and the white horse carrot. Specimens of all 
varieties found on poor soil go to seed as a rule in the autumn and are dis- 
tinguished by a thin, often divided, root which, because of its lignification, 
recalls clearly the ancestral wild carrot. The same behavior is character- 
istic of the turnip-rooted cabbage, Swedish turnip, radishes. Kohlrabi, etc. 

These differences are best made clear by comparing the anatomical 
structures. In Fig. 21 is shown a longitudinal section through a two-year 
old wild carrot. In this figure a is the vertically elongated parenchyma of the 
pith-like central part with scattered spiral, porous ducts ; b the xylem, made 
up of spindle-like wood cells together with ducts and the part of the medul- 
lary ray which extends toward the secondary^ cortex ; c the cambium which 
has become an elongated, thin-walled parenchyma ; d the secondary cortex 
with its resorption spots which follow the course of the latex ducts ; e the 
primary cortex ; / cork. 

Fig. 22 is a corresponding section from a two-year old cultivated carrot. 
The letters in both figures indicate the same parts and a comparison of the 
similarly designated tissues makes very clear the change in the wood tissue 
and the increase in the dimensions of the secondary cortex in the cultivated 
carrot. 

In all tuberous vegetables lignification also occurs normally when they 
grow too old and then this process, as in individuals lignifying prematurely, 
is accompanied by a partial disappearance of the sugar. 

It is well-known, from experience, that many of our vegetable plants 
lignify in hot climates. Precautions against this latter condition will be hard 
to find since the tropical warmth and excess of light favor rapid lignification. 
In cultivation in temperate climates, lignification can certainly be avoided by 
abundant watering and fertilizing; — only care should be taken in this that 
the land is deep and the seed good. Special attention should be given to 
the choice of seed, because seeds from dr}^ localities carry with them a great- 
er tendency to lignification and to a repeated division of the root. 



iSi 

Ball Dryness of the Ericaceae. 

The peculiar sensitiveness of the roots to drought must be taken into 
consideration when growing the numerous species and varieties of the 
Ericaceae as Erica, Azalea, Rhododendron, etc. These plants cannot endure 







2. ^ 




a complete drying out of the roots. While other plants can survive lack of 
moisture, even repeated wilting, without showing any noticeable injury, and 
even continue growth after being again supplied with water, the fine root 
branches of the Ericaceae do not seem able to resume their functioning 
when once entirely diy. In one case I investigated the roots of an Erica 



l82 

gracUis which, after they had dried out, had been subsequently soaked 24 
hours in water, and found that the fine root ends were still shrivelled 
despite the soaking. The character of most Ericaceae, as moor and heath 
plants, is shown by the fact that (with the exception of a few varieties) 
they thrive best in a freely watered, easily drained, aerated soil. In growing 
plants in small pots the need of roots for air must be given the greatest 
possible consideration. The Ericas soon become root bound. The plants 
easily become sour in large pots. The Erica and Azalea drop their leaves 
when dried out. It is wrong, however, to try to repair the previous mis- 
take by setting the pot in water and, after soaking up the earth, to place 
the plants in closed cases in order to reduce evaporation as far as possible 
and to cause turgidity. The plants should be left, on the contrary, in their 
customary place, but strongly shaded during the middle of tlie day. 

Means of Overcoming Lack of Moisture in the Soil. 

If a lack of soil moisture is manifested by the failure of vegetation or 
by its degeneration, as usually occurs more frequently in sandy soils, one 
naturally seeks relief in irrigation when possible. This artificial supply of 
water not only refreshes the tissues, but also, by dissolving the nutritive 
substances in the soil, it is possible for the plant to utilize and distribute 
these. 

Irrigation. 

With the frequent lowering of the ground water level, irrigation be- 
comes a vital question and an acquaintance with the results of Konig's^ 
investigations on the effects of irrigation water is interesting. One learns 
accordingly that when a meadow is being irrigated the water loses much of 
its nutritive material and appreciably more during the warmer seasons, than 
in the colder ones. This loss, however, is not true of all nutritive substances. 
If the carbon dioxid content of the irrigation water .rises, the calcium and 
magnesium nearly always increase instead of decreasing. As in the case 
of carbon dioxid, this quantity seems to rise and to fall with the intensity 
of the oxidation in the soil. In contrast to the above-named nutritive sub- 
stances, potassium appears to be absorbed at any time by the soil since, with 
irrigation, even in the winter, a slight reduction of this important mineral 
can be proved in the water. Sodium, or rather sodium chlorid, just like 
nitric and sulfuric acids almost always showed a slight increase during 
winter irrigation, while during the growing season they decrease, i. e., they 
are taken up directly by the plants. 

Konig concludes that the oxygen of the water acts as a purifier of the 
soil by oxidizing the organic soil contents. This oxygen content varies 
according to the kind of water used in irrigation and the season. Konig 
found it greatest -in spring, smallest in summer, increasing again in the 
autumn. Spring water is much richer in oxygen than river water which 
has passed through inhabited places. The opposite is true of the suspended 



1 Journal fiir Landwirtschaft. Jahrg-. 1880. Vol. 28. Part 2. 



i83 

organic substances which are taken up from the soil by impoverished 
spring water, which has a small oxygen content, but are deposited, on the 
other hand, by the richly saturated river water. 

At a depth of 40 cm. during the colder seasons temperature observations 
show that irrigated land is warmer by varying amounts, even up to 2.8°C. 
To this increase in temperature may be ascribed the fact tliat in irrigated 
meadows, growth begins earlier in the spring and continues later in the 
autumn. 

Konig showed by an experiment in which he artificially mixed sewage 
with the irrigation water, how quickly the subsoil shows its absorption 
qualities, if the soil is not saturated and the irrigation water is heavily 
charged with fertilizing matter. After the water had been used once, it 
could be proved that the soil had taken up 84.5 per cent, of the organic 
substances; 74.2 per cent, of the ammonia; 81.6 per cent, of the potassium 
and 86.8 per cent, of the phosphoric acid. After the same water had been 
used twice again the presence of these substances in it could not be proved 
at all. Of course these figures hold good only for this experiment and vary 
according to the saturation of the soil and water; they have therefore, for 
example, no value in irrigation with liquid manure, in which the soils must 
become surcharged with nutritive substances in a comparatively short time. 
Nevertheless, experiments show what varied advantages can be obtained 
with the right use of irrigation. The importance of watering the soil arti- 
ficially is becoming more and more acknowledged. The best proof is found 
in the transactions of the land cultivation division of the German Agricul- 
tural Society^ in which questions referring to the direct supplying of water, 
raising of the ground water level, have already been brought up. The sys- 
tems known at present have been partially explained by means of illustra- 
tions. The transactions have led to a direct commission from the Directors 
of the society, "that they should take up the question of the watering of 
land with the greatest possible energy." 

Cultivation of the Soil. 

At present, in large plots of land, it is possible only in the rarest cases 
to provide for irrigation without considerable expense and therefore cheaper, 
if less effective, means are more often utilized. Such resources are found 
in working the soil. The breaking up of the soil is most advisable. Some 
practical workers maintain that cultivating the field soil cannot possibly aid 
in the retention of soil moisture, but that this manipulation must rather be 
considered as the quicket way to remove more water from the soil. This 
point of view is erroneous, as is shown by many experiments. The most 
thorough are Wollny's", who has worked with control experiments and has 
found that if the uppermost layers of the soil are broken up, they dry more 



1 Die Moglichkeit der Ackerbewasserung- in Deutschland. Arbeiten d. Deutsch. 
Landwirtsch.-Ges., Part 97, 1904, p. 75. 

2 Wollny, Einfluss der Bearbeitung- und Diingung- auf die Wasserverdunstung- 
aus dem Boden. Oesterr. landw. Wochenbl. 1880, p. 151. 



I §4 

quickly, to be sure, but, by this means, save to a greater extent the water 
supply in the lower layers of the soil. 

The warming of field soil by insolation, its aeration when winds blow 
over its surface and all such influences, remove the water from the upper 
layers of the soil to a greater extent than can be restored by capillary at- 
traction for water from the lower layers. If now, by breaking up the sur- 
face, the interstices between its particles become considerably enlarged, the 
capillarity is decreased and the water no longer rises into the larger in- 
terstices of the now crumbly soil. The more quickly the soil is broken into 
coarsely friable pieces by chopping, hoeing and removing the turf, the more 
the drying out of the lower layers, where the roots are found, is delayed. 

The opposite result is obtained by rolling the field land. In this case^ 
most of the spaces, where capillarity did not act, are rolled close together. 
Capillarity at once becomes active and the upper surface remains moist for 
a longer time. Under certain circumstances, however, rolling may also be 
recommended as a means of retaining moisture in the soil. This will be 
expressly suitable for all very porous soils with a scanty water capacity and 
an abundant subsoil moisture, since, by hardening the surface, its evaporation 
is reduced, while the conducting of water from below is increased. In 
heavy soils, with a high saturation capacity, rolling would naturally be di- 
rectly injurious. 

Mulching of the Soil. 

Instead of breaking up the soil, its surface may be covered with a more 
porous material. In this connection advantageous results can be obtained 
even by covering the surface with sand. This changes favorably the con- 
ditions of moisture and of warmth at the same time, for, according to 
WoUny's investigations', the temperature of the soil is considerably re- 
duced by breaking it up, since the conducting of heat in the friable layer is 
decreased by the considerable amounts of enclosed air. In the same way 
soil provided with a sandy covering is colder in the warm seasons than un- 
covered soil, because the light colbr of the surface decreases the absorption 
of the heat rays, and the considerable amount of water held back under the 
sand is warmed with greater difficulty. If the upper surface of the soil 
itself dries up, its temperature must increase because the evaporation which 
uses up heat is at once prevented. 

Breaking up the soil and covering it, therefore, modify the extremes of 
temperature, but are also valuable in still another way. According to 
WoUny (loc. cit. p. 337), it is shown that during the warm seasons con- 
siderably more water from the same amount of precipitation can filter 
through the soil when covered with sand than through uncovered soil. This 
takes place because the soil covered with a layer of sand (even if only one 



1 Wollny in Oesterr. landw. Wochenbl. 1880. p. 214.- Nessler, Bad. Landw. Corres- 
pondenzblatt 1860, p. 230.- Wagner, P., Vei'suche uber das Austrocknen des Bodens 
bei verschiedenen Dichtigkeitsverhaltnissen der Ackerkrume. Bericht der Ver- 
suchsstation Darmstadt 1874, pp. 87 ff.- v. Klenze, Landw. Jabrb. 1877. 

2 Einfluss der Abtrocknung- des Bodens auf dessen Temperatur-und Feuch- 
tigkeitsverhaltnisse. Forschungen a. d. Geb. d. Agrikulturphysik, 1880, p. 343. 



centimetre thick) remains richer in water, i. e. becomes saturated more 
quickly and therefore lets more water flow into the deeper layers of the sub- 
soil. The same result is shown by covering with ochre, such materials 
as stable manure, straw, tan bark, and even with stones. Soil covered with 
growing plants is even less pervious than the naked earth. 

Some practical workers recommend the use of peaty earth on sandv 
soils. . Thus Walz^ made use of the upper layers of a peaty deposit which 
were 6 to 8 cm. deep and useless for fuel, in order to cover a field of poor 
sandy soil 2 cm. deep, in Februar}^ Later this surface which had been 
covered with peat and one adjoining it, but not so covered, were richly 
fertilized with stable manure. In the heat and drought of summer, 
maize planted on the field mulched with peat showed a better growth and 
furnished a higher percentage of yield. In the same way, later crops were 
found to be more luxuriant on the plat of ground mulched with peat. 

The value of the peat, which Nerlinger- has demonstrated in exact har- 
vest results, arises from its ability to soak up and retain the fertilizing 
substances which otherwise, in sandy soil, would be washed away. I have 
determined experimentally^ that fertilizing makes it possible for the plants to 
give a better yield with less water, which explains the more favorable be- 
havior in time of drought. 

Soils With a Plant Cover. 

It has already been said that soils with a cover of living plants allow 
the least water to drain through. This is explained by the fact that plant 
roots absorb the water. Comparative experiments* prove that the water in 
the soil is more quickly exhausted with a thick stand of plants, even if this 
exhaustion does not increase proportionately to the density of the plant 
growth. 

From these results, the difference between a bare, broken soil and one 
covered with a dense turf during hot, continued dry weather, can be ascer- 
tained. Therefore, in nurseries on porous soil, it is by no means a matter 
of indifference whether it is often hoed or whether turf and weeds are al- 
lowed to form a dense covering. It is not a theoretical conclusion but an 
often demonstrated fact that occasionally premature ripening and sterility 
are produced in fruit trees, because the weeds and turf have taken up the 
scanty supply of water. 

In forestry and trees in beds, if the seedlings do not make a dense 
growth, their development is threatened. Gravelly soils without sufficient 
humus content are also a menace for older plants from 10 to 15 years of 
age, especially if protection is not given on any side by larger plantations. 



1 Zeitschrift d. Landw. Ver. in Bavern 1882; cit. in Biedermann's CentralbL 
1883, p. 136. 

2 Fiihling-'s landw. Zeit. 1878, Part 8. 

3 Sorauer, Nachtrag zu den Studien iiber Verdunstung-. Forsch. auf d. Geb. d. 
Agrikulturphysik, VoL VI, Parts 1 and 2. 

4 Wollny, Der Einfluss der Pflanzendecke und Beschattung- auf die physikalis- 
chen Eigenschaften und die Fruchtbarkeit des Bodens. Berlin, Parey, 1877, p. 128. 



i86 

The forester considers turfed land as a favoring factor, since it retains the 
water of precipitation and by the quick evaporation withdraws the water of 
the subsoil. Places almost circular are sometimes found in forests about the 
base of the trunks where no second growth lives. This circumstance is 
ascribed to the reflection of the sun's rays from the smooth barked, branch- 
less trunks (beeches, birches, firs). The sun rays flashed from the mirror- 
like bark dry the soil to a great extent. This condition can be overcome by 
various means, among which growing plants by natural seeding is recom- 
mended, since the plants so produced will adapt themselves to the locality. In 
places, which must be planted, material should be used which has been 
transplanted once in the nursery and, after the plants are set out, the soil 
should be shaded most carefully. Besides this, all conditions should be con- 
sidered which in general may be recommended for overcoming the lack 
of moisture, such as the protection of seed beds by walls, fences, rows of 
trees, or by closely set brush, hilling and especially breaking up the soil, or 
even fertilizing, since this means a saving of water. Sprinkling with water 
is advisable only in the most extreme cases of necessity. In brushing the 
edges of the beds the use of conifers, especially the Weymouth Pine, is 
most to be recommended, for spruce brush sheds its needles too quickly 
and makes a warmer cover. Fir may easily be set too densely and the 
leaves on branches of deciduous trees wilt too quickly, hence they do not 
afford shade to the soil which dries out too rapidly. 

Wollny has shown by experiments that seed and turf burn out if sown 
too thick, while vegetation on the same plot of land remains uninjured 
if the growth is more broken. 

He found that when the seed had been sown with a drill the soil be- 
tween the rows lost less water than that in the rows themselves and the 
further the plants stood from one another, the more water was retained in 
the rows as well as between them. Therefore, the proper adjustment of the 
quantity of seed to be sown on soils poor in water, will also assist in correct- 
ing injury due to drought\ 

Only in very definite cases can an overplanted soil be proved more ad- 
vantageous than bare soil. By an open growth of short-lived plants as a 
cover crop, water can be retained on sandy soils for later seeds. If seeding 
of the quick growing plants takes place in the autumn or early spring, the 
time these plants most need water will come during the autumnal or spring 
wet season, so that when the dry season comes, they are ready to set fruit 
and require relatively little w^ater; — rather, by shading the soil and by the 
forming of dew, they retain for the more superficial layers a pretty even 
moisture in which seeds sown later, and also delicate seedlings, can be 
developed which otherwise would have dried up on bare soil. 

Forest Litter. 
It should not be forgotten that any covering of the soil retards the 
aeration of the land and therefore, for the maintenance of fertility, the 

1 Oesterr. landw. Wochenblatt. 1880, p. 233. 



i87 

supply of carbon dioxid in the soil must be depended upon to disintegrate 
and dissolve the fragments of rock ; hence great care must be used in the 
choice of the soil covering. How much the mulching disturbs the circu- 
lation of the air is shown by Ammon's experiments\ With 40 mm. of water 
pressure in an hour there passed through a layer of earth 19.6 sc]. cm. in 
cross-section and 0.5 m. deep, the following amounts of air: — 

\\'ith a Grass Covering. Straw Covering. Uncovered. 

1.60 1. 6.30 1. 7.32 1. 

In better aerated soils more carbon dioxid will also be produced and 
this, in spite of its increased elimination into the air, will make itself felt iii 
an increased amount in the soil. The result of letting the soil lie fallow con- 
sists directly in the greater production of carbon dioxid due to the action of 
micro-organisms and to the greater decomposition of the rock debris. 

Another disadvantage of mulching is the lessened availabiUty of the 
precipitation for such covered soil. The amount of this disadvantage will 
vary according to the kind of covering. It will increase with the increased 
sponge-like substance of the covering. Riegler's- statement may serve as 
an example of this diversity. He tested various forest litter and peat moss 
(Sphagnum) as to permeability. Of the 500 g. of water, sprinkled daily in 
a fine stream on the air-dry litter, the following amounts were absorbed or 
ran throught : — - 

Beech Litter Hemlock Litter Sphagnum Turf 

Ran through-absorbed. Ran through-absorbed. Ran through-absorbed. 
1st day.. .400.3 99.7 441-3 5^-7 216.0 284.0 g. 

8th day.. .487.6 12.4 499.6 0.4 493.5 6.5 g. 

This sprinkling corresponded to 10 mm. of rain and accordingly possi- 
bly 20 per cent, of the falling water was retained by beech litter, 12 per 
cent, by fir and 57 per cent, by moss. The mulch was 8 cm. deep all over. 
From Riegler's other tables it is found that, in the next 3 or 4 days, still 
greater amounts were absorbed daily, gradually up to the 9th day the litter 
became so saturated with moisture that almost all the water which fell upon 
it ran ofif. Ten mm. of rain setting in after hot, continued dry weather, w^et 
the earth under the beech mulch only to a depth of 8 mm. ; under the fir 
mulch, 8.8 mm. ; and under the moss, 4.3 mm. Besides this, the conditions 
vary according to the strength with which the water falls on the mulch. If 
the water, finely distributed, was sprayed on the moss cushion, 70 per cent, 
of the given moisture was soaked up, while of the same amount of water, 
supplied in the form of a fine running stream, only 14 per cent, was retained. 

Forests. 

The proximity of larger tracts of trees, viz., forests, must be considered 
as a means of saving the moisture in the soil of cultivated land. According 

1 Biedermann's Centralbl. 1880. p. 405. 

2 Forsch. auf. d. Geb. d. Agrikulturphysik, 1880, pp. SO-96. 



to Matthieu's^ observations, extending over ii years, the air in forests, 
1.5 m. above the soil, is on an average colder than above bare ground, the 
difference being the greatest in summer. The forests exert the same de- 
pressing influence on the mean air temperature as they do on the temperature 
extremes, which are less in forests. When the temperature differences 
amount perhaps to only o.5°C., they are perceptible when a rain cloud passes 
over the region. Air will become saturated above the forest sooner than 
above uncovered land. Thereby the rain will begin sooner and be more 
abundant than on the land which is not forested. In fact measurements of 
Matthieu and Fautrat- prove greater amounts of rain above forests. Hygro- 
metric determinations have shown that the weight of water vapor in one 
cubic meter of air above a spruce forest amounted, on an average, to 8.66 g., 
while above forests of deciduous trees it amounted to 8.46 g. ; above un- 
covered soil at the same height (104 to 122 m. high), at a horizontal distance 
of 100 m. from the conifer forest, to 7.39 g. ; at the same horizontal distance 
from the deciduous trees, to 8.04 g. Thus the proximity of the forest in- 
fluences the moisture vertically and may also exert the same influence 
horizontally. 

Fallow Land. 

"Fallow Land" has less effect on the retention or increase of the water 
supply in the soil than on the accumulation of nutritive substances. Accord- 
ing to Wollny's" statements, the peculiarities of fallow land may be sum- 
marized as follows : — Soil lying fallow is warmer in summer and colder in 
winter. Fluctuations of temperature are greater ever}'where in fallow land 
than in soil overgrown with plants. During the time of growth the soil 
covered by plants has always a lesser water content than when lying fallow. 
This greater moisture content is retained in bare soil even when worked 
more frequently. Bare soil also gains more from atmospheric precipitation 
since, during the time of growth, considerably larger amounts of water per- 
colate through soil lying fallow, than in fields provided with a growing 
plant covering. From the standpoint of nutrition the carbon dioxid con- 
tent of fallow land is most noteworthy. WoUny's researches show that the 
air in fallow soil contains approximately 4 times as much carbon dioxid as 
in grass land. Therefore, the means for the solution of mineral elements in the 
soil are present much more abundantly; which explains in part the greater 
accumulation of nutritive substances in fallow land. This greater enrich- 
ment also depends partially on the quicker decomposition of the organic 
substances because of the greater temperature fluctuations, the increased 
moisture and the more vigorous activity of the micro-organisms. It should, 
however, be pointed out finally that soils with less power for holding water 
and in greater depths (sandy soils) with their greater permeability lose 



1 Matthieu, Meteorologie comparee agricole et forestiere. Paris 1878; cit. in 
Forschungen auf d. Geb. d. Agrikulturphysik 1879, pp. 422-429. 

2 Fautrat. Ueber den Binfluss der Walder, den sie beriihrenden Regenfall 
und die Anziehung der Wasserdampfe durch die Fichten. Aus Compt. rend. 1879, 
Vol. 89, No. 24; cit. Biedermann's Centralbl. f. Agrikulturcliemie. 1880, p. 241. 

3 Wollny, Die Wirkung der Braclie. Allgem. Hopfenzeitung 1879, Nos. 55, 56. 



1 89 

considerable part of the plant nutritive substances which are washed away 
into the subsoil. Such soils therefore, conversely, must be kept under a 
covering of plants. 

Local conditions must show which one of these means can best be used 
to prevent a lack of moisture. In any case it is evident that we do not stand 
powerless in the face of drought. 

b. Loamy Soils. 
General Characteristics. 

In considering physical influences injurious to vegetation, we need not 
distinguish between loam and clay soils. We are concerned always with 
mixtures of clay and sand and only the proportions of these two elements 
differ. The sand content decreases more and more from sandy or "mild" 
loam to strictly loo my soil and to clay soils, which are plastic in a damp con- 
dition ; in them predominate the fine particles so easily washed away. In 
our agricultural land, mixtures of lime and humus will also be of importance 
as modifiers. Lime will make heavy soils more open by increasing their 
friobility. 

Fertility is directly dependent upon friability, hence plastic clays are 
sterile. Non-friable clay soils are impervious to water, and, in level places, 
easily give rise to the formation of swamps. The smaller the size of the 
soil particles, the greater will be their water absorptive power so that very 
significant changes in volume occur with extensive, rapidly successive differ- 
ences in the supply of water. LTpon this depends the characteristic cracking 
of clayey soils when drying out. Soluble salts can be washed out of clay 
soils only with difficulty. 

This drying out is much more dangerous as the soil approaches pure 
clay. When once dr}% clay takes water up again very slowly since it 
can penetrate only with difficulty between the closely packed soil particles. 
These peculiarities decrease proportionately as the admixture of sand in- 
creases. Drying out in summer becomes at times more dangerous in heavy 
soils than in sandy, especially if a vigorous grow^th of trees has developed 
in regions which at best are poor in precipitation. The summer rains do 
not then suffice to make good the loss of water. These soils are dependent 
on the winter moisture. Hence the plant growth suffers here much more in 
dry springs, in years when the winter moisture has been less and the snow 
covering has failed, than on sand. This explains the fact that, after hot, 
dry summers and winters, poor in precipitation, a blighting of the tops of 
old trees (i. e., a drying of the branches) sets in because of the lack of 
moisture, even if the spring has abundant rain. Sandy soils with moderate 
spring rains are saturated more quickly and the water is at the disposal of 
the roots. 

Heavy soils remain "cold." This is explained by their high water con- 
tent which increases with the fine granular structure. In many regions im- 
ported conifers (Abies Pinsapo, Biota orientalis aurea, Taxus hibernica, 



190 

Picea orientaUs) die quickly. This is ascribed to winter frost but upon 
closer observation it is discovered that low temperatures become harmful 
only when the soil is very wet^. 

A deficiency of soil aeration is the most harmful factor since upon the 
aeration depend the phenomena of decay in the decomposition of organic 
masses. Thus in judging loamy soils as to their fertility not only the de- 
gree of friability, but also the depth to which this extends, becomes decisive. 
Since the firm loam layers of the subsoil are aerated only with difficulty, 
the spreading out of the root system takes place only in the friable layers. 
Therefore a special value should be laid on the maintenance of this friabil- 
ity. This must be taken especially into consideration in forests, where the 
litter IS constantly raked away. Ramann's investigations- show that, in re- 
moving litter, the soil becomes densely packed and works harm to the 
forest tract. 

The packing of soil and the necessity for loosening it should especially 
be considered in growing all tropical plants, as Vosseler" has proved. 
He describes the soils characterized by Koerts as "older red loam," and 
especially the primeval forest soil of East Usambara thus; — "The red 
soil consists mainly of fine loam and clay which is pervious but too finely 
porous to take up small humus particles ; besides, chemical action 
takes place possibly in the upper surfaces alone and thus prevents 
their penetration into the lower soil. Since the soil itself is the final pro- 
duct of decomposition, it lacks the advantage of i)rocesses of loosening up 
which possibly take place during such action." Here also, therefore, the 
loosening of the soil is given as the first requirement for successful culti- 
vation. 

The more clayey the soil is, the more slowly the vegetable refuse will 
be decomposed because of the lower temperature. While in sufficiently 
friable soils, a normal decomposition takes place, masses of raw humus 
collect on thick clay soils, i. e., particles of plants, which are only slightly 
decomposable, remain deposited on the soil because the conditions are un- 
favorable for decomposition. If very fine grained soils with a greater 
moisture holding capacity, i. e., ability to retain large amounts of water 
w ithout giving it ofl^ in the form of drops, acquire so much water that it 
overcomes the continuity of the substance particles by penetrating between 
them, thus forcing them apart, the soil becomes softer. This condition is 
especially peculiar to strong clay and red soil ; such a disintegration occurs 
less frecjuently in loamy soil. 

Such reduction of the soil is doubly dangerous, if it takes place in the 
autumn or spring. On the one hand, the soil washes away at once and the 
seeds are soon exposed to drying or to freezing as the case may be. On the 



1 Cordes, W., Fieitrag- zum V'erhalten der Coniferen gegen Witteriingseinflusse. 
Hamburg- 1S97. 

2 Ramann, E., Untersuchung streuberechter Bdden. Sond. Z. f. Forst- u. Jagd- 
wesen, XXX .Jahrg; cit. Bot. Jahresb. 1900, II, p. 415. 

^ Vosseler, Ueber . einige Eigentiimlichkeiten der Urwaldboden Ostusambaras. 
Mitteil. a. d. Biol. Landwirtsch. Institut Amani, 1904. No. 33. 



191 

other hand, this condition also retards working the soil and planting the fields, 
thus becoming a cause of poor harvests. Especial consideration should be 
given to the fact that, for all our cultivated plants, the usual planting time 
has been determined by observing the behavior of the plants in our climate. 
It can be shown at any time that variation in the periods of cultivation pro- 
duces changes in the character of the plants (the change from winter to 
summer grain). Such a delay of the seeding time often acts injuriously, 
as, for example, in peas. The same seed that furnishes a fine crop of healthy 
plants, when sown early in spring, very often produces low plants with 
small pods, greatly injured by mildew, if sown in summer. Kohlrabi, planted 
too late in spring, easily become woody, etc. 

Similar phenomena may be observed in fine sandy heath soils (loose 
loam). Grabner^ characterizes this form of soil as consisting of sand grains 
almost as fine as flour with only small clay admixtures. The whole mass 
when wet looks like loam. In a dry condition, however, it may be dis- 
tinguished from loam proper by its porosity. Thus, as a result of its very 
fine granular structure, it can become as hard as stone. In places which 
are cultivated constantly and kept loose by means of animal manure, such 
soil is often valuable but in forestry it is not, for, after the usual single 
loosening, the fine sand is at once packed together by rain and too little 
oxygen from the air can get to the roots of the trees. 

The Covering of Soil with Silt. 

In heavy rain storms and floods soils with a large content of very finely 
broken particles are washed together and, after the evaporation of the water, 
are left in the form of a thick, close crust. The moisture holding capacity 
of a soil increases with the fineness of its pulverization, as has been men- 
tioned above. Increased pulverization of the particles deepens the upper 
surface and the power for retaining water depends on surface attraction. 
By pulverizing a soil mass, consisting of coarse pieces of quartz from i to 
27 mm. in size, which had an absolute saturation capacity of 7 per cent., the 
capillary absorptive power was so increased that a fine sand produced from 
the quartz, the size of its grains being 0.3 mm., held back more than 6 times 
as much water. One sees that under certain circumstances the kind of 
mineral may be unimportant and only the mechanical constitution of value ; 
that, therefore, even quartz dust can assume the role of clay. Naturally 
this dustlike sand has no coherance whatever, and can therefore never in 
itself take over the role of a binding substance such as clay. Principally, 
however, it is clay soils which suffer from erosion in the form of silt and, 
by making air tight layers, cause the decay of seeds and plant roots. At 
times the roots form accessory organs in order to find the necessary air in 
marshy soils. In this connection, attention should be called to the knee-like 
outgrowths of roots which struggle to the upper surface of the soil, as those 



1 Grabner, Handbuch der Heidekultur, 1904, p. 200. 



192 

of Taxodium distichum and of Piniis serotina which are not formed on dry 
soils, and are described by Wilson' as aerating organs. 

An example of the injury to vegetation, due to a direct deposition of 
silt, is furnished by Robinet- of Toulouse, where the nurseries had stood 
for only two days under water. At the base of some plants very little mud 
was deposited. These remained healthy. But when the mud covered the base 
of their trunks, possibly 10 to 12 cm. deep, the damage was great. Almond, 
acacia, cherry (even the mahaleb cherry) mountain ash, Ligustrum, Ma- 
honia, Evonymous and most conifers were killed. Individual specimens of 
Crataegus, Pirus Communis (of which those grafted on the quince suffer 
less) Pirus Malus, Castanea, Mespilus, Catalpa, etc., which had stood 8 to 
10 days under water, blackened at the base and died when the silt was not 
removed. Platanus. Alnus, Ulmus did not suffer, and Populus, as well as 
Salix (weeping willow), developed many roots from the base of the trunk out 
into the silt. All the specimens of Sophora, Fraxinus, Carpinus, Fagus, 
Betula and Robinia did not die ; the leaves of the survivors, however, turned 
yellozv. The linden and chestnut lost all their leaves. Evergreen plants, 
and even a part of the conifers, lost their leaves when they had been covered 
by water. 

Of double importance is this change in the physical constitution of the 
soil in regions exposed to frequent inundations and, among them, the soils 
suffer most which are flooded by sea water. Aside from the injury to vege- 
tation from the large salt content of the- soil, there is found, according to 
A. Mayer^, as a resulting phenomenon of a dense covering, noticeable at 
times only in the second year, a formation of a black layer, strongly im- 
pregnated with iron sulfate, which may further injure vegetation. 

Von Gohren* also emphasizes the formation of such kinds of ferrugi- 
nous layers called "Knick" in West Friesland in very humus, loamy and 
clayey mud deposits of sea and river m.arshes and explains their production 
by the fact that the ferric oxid in the loam is reduced to ferrous oxid by 
the organic substances in the absence of air. This ferrous oxid combines 
with the crenate acid to form crenic ferrous oxid. Crenic ferrous oxid, 
distributed in every direction, is gradually oxidized again, cements together 
all parts of the soil as ferric hydroxid and co-operates in the formation of 
meadow ore of such ill-repute. We will finish considering the formation of 
meadow ore when discussing the peculiarities of swamp soil and now turn 
first to the phenomena of silt covering under the influence of salt solutions 
found in the use of fertilizing salts. 

Mayer's experiments show that particles of clay suspended in water 
are precipitated differently when they are in suspension in pure water or in 
water containing sodium chlorid and other admixtures. In pure water 



1 Wilson, W. p. The production of aerating organs on the roots of swamp and 
other plants; cit. Bot. Jahresber. 1889, I, p. 682. 

- Revue horticole; cit. Wiener Obst- u. Gartenzeitung 1876, p. 37. 

3 Mayer, A., Ueber die Einwirkung von Salzlosungen auf die Absetzungsver- 
haltnisse toniger Erden. (Forsch. auf dem Gebiete d. Agrik.- Physik. 1879, p. 251.) 

4 von Gohren; Boden und Atmosphare. Leipzig 1877, p. 56. 



193 

the particles are deposited according to size (more exactly, according to the 
proportion of their surface to their mass). The finest particles remain un- 
commonly long in suspension since they are held by the attractive power 
of the water, which is almost comparable to a chemical solution. The at- 
traction of gravity for these particles is powerless in opposition to this 
attraction. After the clay, which has been dissolved in a glass cylinder for 
the experiment, precipitates from a salt solution, it is noticeable that a layer 
consisting of close, fine clay particles has formed with a comparatively very 
clear fluid above it. Because of the presence of sodium chlorid, all fine 
clay particles are precipitated more as a whole (coagulated, according to 
Schlosing). "Flocculency" is thus produced. The fall of the somewhat 
coarser particles among these appears to have been held ba^k, while that of 
finer ones has been somewhat hastened. It has been assumed that probably the 
presence of the salt has decreased the attraction between clay and water, 
since the w-ater then lets the clay fall more completely. On the other hand 
the attraction of clay to clay must have been increased, and it is therefore 
more compact. Durham- explains the process by the fact that every bit of 
the attraction of the water otherwise required entirely for the suspension of 
the clay is satisfied by the salt of the solution. According to him, sulfuric 
acid acts like the solution of sodium chlorid, and, according to Mayer, all 
mineral acids behave in the same way. The same is true of mineral salts 
even in an excess of fixed alkali or ammonia. 

According to the theories now prevailing, electrolytes act flocculently. 
i. e. all bodies which in an aqueous solution are partially split up into "Ions." 
Non-electrolytes have no action. At any rate, an electric current precipi- 
tates the flakes. It should therefore be assumed that the particles distributed 
in the water are charged with electricity and the cause of the oscillation may 
be sought in this electric charge^. 

The chief point, worth considering for all cultivated clay soils, lies in 
the fact that the nitrates, so far as deposition of the clay is concerned, ap- 
proximate the chlorates and, on account of the ease with which they are 
washed away, rapidly cause the packing of the soil. By this is explained the 
mechanical destruction of soils rich in clay, when repeatedly fertilized ex- 
clusively zvith nitrates. At first fine crops are obtained but later retrogres- 
sion takes place. Sodium chloride fertilising used for certain plants has 
naturally the same destructive effect. 

Behrens* calls attention to the real disadvantage of an excessive use of 
fertilizing salts. Their osmotic action comes especially under consideration. 
Because of this osmotic action of the soluble salts in the soil, it is more 
difficult to supply the water needed by the plant and the plant responds by 
a suitable modification of its organs. In correspondence with the physiolog- 
ical lack of moisture, the plant reduces its evaporation by forming fleshier 

1 Biedermann's Centralbl. 1883, Nov., p. 786. 

2 Chem. News; cit. "Naturforscher" 1878. p. 112. 

" Ramann, E., Bodenkunde, 2nd. Ed.. Berlin. .J. Sprinfrer, 1905. p. 225. 
■i Behrens, J., Ueber Diangungsversuche. Jahresb. d. Vertreter d. angewandten 
Botanik, II Jahrg. Berlin, Gebr. Borntrager, 1905, p. 28, 



194 

leaves with smaller intercellular spaces ; this may be found in plants near 
salt springs and on the sea shore. 

Among our cultivated plants, tobacco suffers most; it reacts exactly 
as in hot, dry summers and forms fleshier leaves with a reduced burning 
quality. Hunger^ confers these observations, made in Europe, and says 
of the cultivation of the Dehli-tobacco on Sumatra, that the leaf most 
valued, most grown and most carefully selected, is large, thin, poor in oils, 
and develops only in the presence of abundant water as in continued rainy 
weather, while in dry weather small, thick, less valuable leaves, covered with 
many glandular hairs, are formed. 

The Improvement of Soils Which Are Becoming Compact. 

The improvement of the easily packed clay soils will have to lie in the 
increase of their ability to be worked. Heavy soils are unyielding, i. e.. they 
offer great difficulty by sticking to the farm implements, when damp, and by 
hardness, when dry. Great clods are produced which generally do not fall 
apart easily if the clay or red clay soil is poor in humus. It is well-known 
that the best plan for working soil for spring planting is to break it up in 
the fall and let it lie in rough furrows. The freezing of the water in the 
interstices during the winter months reduces the tough clods to a mellow 
crumbling mass. 

These advantages are available only for spring planting and disappear 
after the heavy rain storms of the summer. Therefore care must be taken to 
prevent caking by supplying humus or marshy earth ; fertilizing with long 
strawy manure is very greatly used. However, Umintj and marling the soil 
have given very effective results. Practical experience has shown that the 
addition of calcium, which is in solution in the soil as the bi-carbonate, will 
hinder its caking. 

A definite amount of all salts, even of the most effective, calcium and 
magnesium, must be kept in solution in excess of the amount necessary to 
start action if any deposition of the clay particles is to take place. Even in 
rivers the flocculent action of dissolved salts makes itself felt since, for 
example, the sediment in rivers flowing from lime regions is more quickly 
deposited than in those from regions poor in lime-. For agriculture, fria- 
bility becomes directly important since upon this depends the proper state of 
tillage. The small bits of the soil behave similarly to the clay flakes. Hil- 
gard proved the action of lime by tempering solid clay soils with i per cent, 
quicklime. While the original clay soil became as hard as stone after drying, 
that mixed with lime was found to be crumbly and mellow. Since, besides 
a continuous mechanical working of the soil, the salts also condition its 
looseness, this must be the case, to an equal extent, in forest soil also. If 
the soluble salts, determining the friable structure, are decreased, as by 
excessive use of litter, covering with raw humus, the leaching of the upper 
layers, etc., a packing of the soil must take place. 

1 Hung-er, F. W. T., Untersuchungen und Betrachtungen liber die Mosaikkrank- 
heit der Tabakpflanze. Zeitschr. f. Pflanzenkrankh, 1905, Part V. 
- Ramann loc. cit. p. 226. 



195 

A top dressing of waste lime from sugar factories is often made use of 
in the cultivation of beets. The mechanical efifect makes itself felt not in- 
frequently by the fact that, as a result of increased capacity for being heated 
and the scanty supply of water, these soils later cause heart rot and dry rot. 

Hilgard's statements^ on the "alkali soils" of California are of great 
interest. The alkali places often found between excellent cultural lands con- 
tain so much salt that they become noticeable by efiflorescence on the surface. 
Those which contain alkaline carbonates (and partially also borates) are dis- 
tinguished by the difficulty or almost impossibility of producing a really 
friable soil. After each rain, a coffee brown, clay water, colored by dis- 
solved humus, stands at times for weeks on those places, recognizable be- 
cause of their lower position. The same working of the soil which gives 
good soil the consistency of loose ashes makes the alkaline land a mass of 
rounded clods varying in size from a pea to that of a billard ball. 

After evaporation, heating and saturation with carbon dioxid, the 
blackish brown solution, leached from alkaline soil, gives 0.251 per cent, in- 
combustible residue. Of this 0.158 per cent, was redissolved in water and 
this soluble part consisted of 52.74 per cent, sodium carbonate, 33.08 per 
cent, sodium chlorid, 13.26 per cent, sodium sulfate, 1.83 per cent, sodium 
triphosphate. 

The 0.093 PC cent, insoluble residue from the heated water extract con- 
tained 14.02 per cent, calcium carbonate, 5.37 per cent, calcium triphosphate, 
5.77 per cent, magnesium triphosphate, 24.37 P^^ cent, silica soluble in 
NaoCo.,, 50.47 per cent, of ferric oxid, aluminium oxid and some clay. 

In this case, as well as in many other alkaline soils in California, the ad- 
dition of a sufificient amount of gypsum (land plaster) produces a striking 
effect. The caustic action of the alkaline carbonates on seeds and plants 
stopped at once so that where previously only "alkali grass" (Brizopyrum) 
and Chenopodiaceae grew, maize and wheat were produced without difficult}'. 
The gypsum naturally requires a longer time for the mechanical change of 
the soil surface and its greater loosening. 

Inundations. 

In opposition to the frequently widespread anxiety when volumes of 
water break over cultivated land, it might be emphasized that, naturally, 
aside from the washing away of nutritive substances and the mechanical 
injury due to the pressure of the waves, vegetation is not extremely sensi- 
tive to a water cover over the soil for some time. A\^oody plants especially, 
as floods show, possess a great power of resistance, which continues as long 
as the water keeps moving. 

Stagnant water, remaining for a long time on the surface of the soil, 
works the greater harm ; for a shorter time, inundations in the form of 



1 Hilg-ard, Ueber die Flockung- kleiner Teilchen und die physikalischen und 
technischen Bezichunsen dieser Erscheinung. American Journal of Sciences and 
Arts. XVII, March 1879. For.sch, auf d. Gebiete d. Agrikulturphysik, 1879, p. 441. 



196 

dammed up water may come under the head of useful factors of cultivation. 
At any rate inundation will always' be more dangerous than those methods 
of irrigation where the soil always remains accessible to the air. The oxygen 
content of irrigation water increases oxidation in the meadow soils since 
water filtering ofif through the soil shows a lesser amount of oxygen and, at 
the same time, an increased amount of carbon dioxid and sulfuric acid in 
comparison with water in use for irrigation^. So long as sufficient oxygen 
is present the slow phenomena of oxidation of organic substances into 
carbon dioxid, ammonia and nitric acid, which we term decomposition, are 
accomplished chiefly by the action of micro-organisms. If a scarcity of 
oxygen occurs, however, due to continued retention of the water, that 
process of decomposition begins, partly of a purely chemical nature, partly 
with the co-operation of bacteria, which we call decay, whose final products 
are compounds which may still be oxidized. 

If the water accumulates in places where impervious layers of soil 
entirely prevent any vertical flowing away and all horizontal flowing away 
is also made difficult, the land becomes marshy. 

With the excessive wetting of the soil, the symptoms are again seen, 
which usually appear gradually with root decay. In deciduous trees, 
especially fruit trees, and with grapes a premature yellow leaf (chlorotic) 
condition becomes noticeable, which advances from below upward. This 
advancing death and falling of the leaves from the base of the branch to- 
ward its tip bear witness to the fact that the growing branches strip ofif their 
older leaves in order to mature their younger ones, which happens also in a 
gradual drying up. By this means, yellow leaves ma)^ be distinguished from 
the pale leaves resulting from the action of frost, in which the young leaf 
apparatus is disturbed and its normal chlorophyll action retarded. 

Conversion of Land Into Swamts. 

R. Hartig's- observations show that stagnant water is most injurious in 
forest plantations since the sensitiveness of the trees to frost is increased 
and freezing and heaving occur in the seed beds. Hartig'' observed decay 
of the roots to a devastating extent in the tracts of the young pines in 
Northern Germany. It begins between the 20th and 30th years when, after 
a short period of weak growth, the trees, still covered with perfectly green 
needles, topple over as soon as a weight of snow touches them or a high 
wind acts on them. It is found that the tap root (see Growth of Stilts, p. 92) 
is wet and rotted up to the base of the trunk while most of the lateral roots 
appear to be healthy. Such a decay of the roots may indeed be found in 
spruce plantations, but it is less noticeable because the superficially extended 



1 "Wollny, E., Die Zersetzung der organischen Stoffe und die Humusbildung'en. 
Heidelberg 1897, Carl Winter, p. 351. 

- Hartig, R., Lehrbuch der Pflanzenkrankheiten, 3rd. Ed. Berlin, Springer 1900, 
p. 263. 

3 Die "Wurzelfaule, Zersetzungserscbeinungen des Holzes, Berlin, Jul, Springer, 
J878, p, 75. 



197 

root system makes the tree less dependent on the few roots growing down 
deep into the soil. 

It may be observed, especially in the province of Brandenburg, that the 
healthy condition of pines ceases if the sand flats most suitable for this 
growth have depressions in the ground where the accumulated water forms 
marshy pools. Up to the edge of these marshy places the trees stand erect 
and are comparatively long needled. At the point where the black moor 
begins, the growth becomes weakened, the needles shorter and the tree 
shows very small annual rings which not infrequently cease entirely. 

In the increased planting of the very profitable pine trees, carrying 
them even on to damp soils, it is not surprising that root decay is found 
there to a very marked extent. It is advisable to limit the culture of pines 
to sandy, open positions and to choose for heavy, wet soils, such species of 
trees as are found by experience to best endure moisture. In places where 
no definite agricultural system regulates the tracts, the suitable kinds of 
trees make a natural appearance in the course of years, because of their 
greater power of resistance in the struggle for existence. It is approximately 
the same as the gfadual control of the position in frost holes by the kinds of 
trees which resist frost (hornbean, birch, aspen). The red alder can best 
endure the strain of stagnant water. Besides this, black and silver poplars, 
as well as most willows and the sweet birch, thrive on moist soils. The ash 
is often found also, but under these conditions the trunks are entirely 
covered with moss and canker-like swollen spots. 

In order to overcome the injury due to turning land into swamps, its 
cause must be determined exactly. At times the condition is due only to a 
lack of air circulation, and here the partial clearing of the land of its tree 
vegetation by the removal of the undergrowth and the lower branches of the 
trees, together with proper thinning, would be beneficial. Even when the 
land only becomes slightly swampy, especially in mountains, it may be re- 
stored by planting with conifers (Spruces). This holds good for the cases 
when increased evaporation of the upper surface is sufficient to overcome the 
accumulations of water in the soil. As the trees grow, and because of their 
close proximity, their evaporating surface not only increases but also less 
and less water can fall to the soil, because of the thick shelter of leaves. 

The very radical means of removing the water by drainage or ditches 
should be used in forest tracts only after careful consideration of all local 
conditions since this method is often attended by greater disadvantages than 
advantages. This is especially true in mountain forests where the lowering 
of the water level of one district may easily have wide spread effects on the 
surrounding region. In some cases, areas, especially slopes, with a strong 
tree growth, where there is no excess of water, become drier. Trees accus- 
tomed to the former amount of moisture deteriorate and may partially die. 
On plains such sharp changes due to drainage are less to be feared. 

It would not be necessary to further discuss the formation of marshes 
if, aside from the exhalation of gases, injuries to cultivated land did not 



I. 


11-75 


COo 


2.48 CH, 


2. 


12.62 




5.68 '' 


3- 


34-99 




29.03 " 


4- 


55-81 




42.54 " 


5- 


56.00 




42.70 " 


6. 


45-9 




54-1 " 


7- 


43-3 




56.6 " 



198 

follow attempts to drain the marshes and boggy places. The injury to 
meadows should be considered especially in this connection on account of 
the frequent use of injurious marsh and boggy water for irrigation. The 
conversion of irrigated meadows into marshes by overfilling the soil with 
sewage may be considered only in passing. 

The statements of Bischof and Popoff^ should be cited in connection 
with the exhalation of gases. The gases produced are often rich in hydro- 
carbons, especially methane or marsh gas (CH^). Popofif investigated the 
gas developed in a cylinder which contained a slimey mass consisting of 
kitchen refuse and substances of similar character. This slime was kept 
33^ weeks in the cylinder, at first at 17° C, later at 7 to io°C., and gave 
gas mixtures of the following percentages of composition in the successive 
investigations which took place usually at intervals of 2 to 4 days : — - 

4.71 O. 81.06 N. 

81.70 

0.0 O. 35-98 N. 
0.0 " 1.65 " 

0.0 " 1.30 " 

0.0 " 0.0 " 

0.0 " 0.1 " 

These figures show that at the beginning of the experiment part of the 
air found in the cylinder was driven out, and part used up, while the oxy- 
gen oxidized the organic fragments in the slime. So long as free oxygen 
was present, the formation of carbon dioxid exceeded that of marsh gas,- — ■ 
on the other hand, this proportion was reversed as Soon as the oxygen was 
exhausted. 

Proceeding with the hypothesis that it is the cellulose in the slime 
which is decomposed, assisted by the action of the lower organisms, Popoff 
put clean filter paper with a small quantity of slime into a flask. On investi- 
gating the gas formed after some little time, he found its composition to be 
34.07 per cent, carbon dioxid, 37.12 per cent, marsh gas, 1.06 per cent, hy- 
drogen and 27.75 per cent, nitrogen. 

Near marshes, however, we also frequently detect the odor of hydrogen 
sulfid. This comes partly from the decay of protein bodies which form 
leucin, tyrosin and other substances by their decomposition and finally car- 
bon dioxid, marsh gas, ammonia, etc. Erismann's- observations, cited by 
Detmer, make possible the determination of the quantitative composition of 
the gas given off in 24 hours from 18 cubic m. of excrement placed in a 
poorly ventilated cess pool. 

The whole mass gave 11. 144 kg. carbon dioxid, 2.040 kg. ammonia, 
0.033 ^S- hydrogen sulfid and 7.464 kg. marsh gas. In this decomposition 
oxygen and nitrogen were also set free. 13.85 kg. of oxygen are said to have 
been taken up by the 18 cubic m. in 24 hours. 



1 Bischof's Lehrbuch der chemischen und physikulischen Geolcgie, 2nd. Ed. 
Popoff in Pfliiger's Archiv f. Physiologic, Vol. X., p. 113. 

2 Zeitschr. f. Biologie, Vol. XI, pp. 233 ff. 



199 

Thus a comparatively very slight development of HoS is found and it 
must be assumed therefore that, if large amounts of HoS are formed in 
marshes and other places, they must owe their origin to a reduction of sul- 
fates in the soil, conditioned by the organic substances present. 

PageP and Oswald summarized the results of their investigations on 
such reduction processes in the substances of marshes and found that, in 
the absence of air, sulfur metals occur, as well as hydrogen sulfid, and 
that, together with this reduction of the sulfates, ammonia is set free from 
the marsh substances containing nitrogen. The authors do not state defi- 
nitely whether these substances are produced only in the absence of air, but 
in their production may lie the harmful quality of stagnant water. 

The Burning of Plants in Moist Soil. 

In summers, remarkable because of great temperature extremes, it has 
been observed that on hot, clear windy days, plants of rapidly growing, large 
leaved crops, such as hops, wilt greatly, particularly when grown in damp 
places. The lower and middle leaves of plants growing in damp hollows 
are sometimes seen to turn yellow and brown at the edges and partially to 
dry up so that they can be rubbed to a powder in the hand. These specimens 
have been partly burned by the sun. The noticeable feature is that the 
burning takes place directly on those places in the field, in which, through- 
out the whole year, sufficient moisture is present, while in higher, drier 
portions, still more exposed to the wind, the plants usually suflier less. My 
comparative experiments- throw sufficient light on such cases. They prove 
that plants, which from the beginning produce their roots in a soil contain- 
ing much water or even in water cultures, evaporate much more water per 
square centimetre than do plants of the same strain grown under conditions 
exactlv similar except with a lesser water supply. It is an interesting but 
not very well-known phenomenon that many of our cultivated plants from 
very different families grown under optimum conditions, in producing one 
gram of mature, dry substances, evaporate approximately equal quantities 
of water,, — indeed the transpired water varies from 300 to 400 g. in amount. 
If the plants grow in localities which, like soils with an impervious subsoil, 
constantly have a great deal of water at their disposal, a constant nutrient 
solution will be present in the interstices of the soil, more or less highly con- 
centrated according to the soluble materials present. If the concentration 
exceeds the amount favorable for the plant species, the plant grows less 
vigorously, remains short-limbed, small-leaved, but usually dark green. If 
the concentration is exactly right, the growth is very rich and luxuriant 
and the absolute water requirement is very great, but is small if reckoned per 
gram of dry material produced. Under such conditions the plant finds the 
soil water of great value. In excessively damp places, however, it often 
happens that the soil solution is poor in different nutritive substances. 



1 Landwirtsch. Jahrb., Vol. VI, Supplement, p. 351. 

2 Sorauer, Studien iiber Verdunstung. Forsehung-en auf dem Gebiete dei" 
Agrikulturphy.sik, Vol. Ill, Parts 4 and 5, pp. 43 ff. 



:2o6 

The weather requirement is greatest under such conditions just as if 
the plant made the greatest struggle to produce as much as possible from 
the very scarce nutrient substances present. The leaves, then formed, are 
very large and well spread, but are very little resistent to cold as well as to 
heat. They react unfavorably to influences which pass over other plants 
without leaving any ill effect. 

Such disturbances occur earlier in plants in moist localities. On hot 
and especially windy days, evaporation is enormously increased, the amount 
of water transpired is then considerably greater than that supplied by the 
axial organs. Consecjuently the leaves on many plants wilt. The smaller the 
normal transpiration per square centimeter surface, the longer the amount 
of water brought by the stem, even on extremely hot days, will compensate 
for the loss of transpiration. The plants of damp localities which, as ex- 
perimentally determined, evaporate much more water in the same unit of 
time than do plants from dry places, have thereby first of all reached the 
limit when lack of moisture in the cell acts injuriously. In these plants the 
leaves dry up first and not the very youngest nor the very oldest but, as a 
rule, those working most actively and in part still elongating.. 

Proper drainage to remove the water from those particular tracts of 
ground is the surest method of overcoming the trouble. 

Delayed Seeding. 

As a result of damp soil the time for planting is frequently delayed. 
The following are the results of experiments by Fr. Haberlandt^ and H. 
ThieP. The most detailed experiments were made by Haberlandt in 1876 
with four kinds of summer grain in which, on the ist and 15th of the months 
April, May and June, the seed was sown on a bed 3 sq. m. in size. The 
results may be summarized as follows : The amount of harvest in all sum- 
mer grains decreased more and more as the seeding was delayed. This was 
based first of all on the considerably weaker growth of the grain planted 
late and was most evident in the smaller number of fertile stems. A de- 
crease not only in the quantity, but also in the quality was very noticeable. 
The weight in straw increased with delayed sowing. In general the chafif 
and roots of the crop increased disproportionately to the weight of the grain. 
The quality of the grain itself also decreased greatly. Barley and oats from 
later sowings had a greater amount of chaff by weight; the smaller the in- 
dividual grains were, the greater this disproportion became. 

The later sowings were attacked to a greater extent by ergot, mildew, 
rust and especially by leaf lice. Besides this, up to the time of forming the 
blades, as well as blossoming and ripening, they required a greater amount 
of heat than did earlier sowings. Even the germinative power of the har- 
vested grain was affected and of a lowered quality in seed from plants of 



1 Haberlandt, Pr., Die Beziehungen zwischen dem Zeitpunkt der Aussaat und 
der Ernte beim Sommergetreide. Oesterr. landw. Wochenbl. 1876, No. 3; 1877, No. 2. 

2 Thiel, H., Ueber den Einfluss der Zeit der Aussaat auf die Entwicklung des 
Getreides. Ref. in Biederm. Centralbl. f. Agrikulturchemie. 1873, p. 47. 



20 1 



late sowings. In the first place, the percentage of germination was lower; 
in the second place, the grain from late sown and late harvested seed also 
recjuired a longer time for germination. From Haberlandt's earlier investi- 
gations in this line, showing a lesser development of grain in bulk as well 
as in absolute and specific weight, it is further seen that the amount of soil 
moisture alone is not the only cause of the difiference between late and early- 
sowing. In these experiments the plants had a sufficient water supply, from 
the beginning, and yet showed these different proportions. 

Thiel's experiments with late sowings were made at various times in the 
autumn. The time of harvesting for all the plants, even of widely different 
periods of sowing, was approximately the same, but very late sown seed 
had a very small yield so far as it remained alive at all. Indeed Thiel rightly 
calls attention here to the fact that late sown seed sprouted simultaneously 
with that sown earlier with corresponding spring weather, without, however, 
having had time to collect sufficient material for an abundant development 
as did the plants grown from seed sown earlier. Naturally the constitution 
of the seed plays a considerable role here. The older the seed, the more 
slowly the reserve substances are mobilized. With ripening and subsecjuent 
maturing, the amounts of sugar and amido nitrogen compounds decrease^ 
and do not become prominent again until germination. The more or less 
favorable sprouting of the seed depends on its age and the soil constitution. 
At this point we will insert the warning that no reliance should be placed on 
the results of other germinative tests, but one's own soil must be tested di- 
rectly as to its behavior with dift'erent seeds. Seed which keeps well, accord- 
ing to common germinating tests, may give poor results, especially in heavy 
soils and, conversely, a light soil may often help seed to make a good growth, 
which developed only a moderate quality in the germinating bed. Hiltner's" 
report, for example, on newly harvested rye, which had suffered from a 
thunder storm, showed that it grew well in some fields, but absolutely would 
not grow in heavy soil. In another case, rye, developing 97 per cent, seed- 
lings in a germinating test, molded almost entirely on one field, while in an 
adjacent one it gave normal growth. 

Souring of Seed. 

In the section on too deep sowing (p. 106) we have already considered 
the disadvantages to which seed is often exposed in heavy or in incrusted soils 
with a large water content. Even germinated seed has to struggle against 
difficulties due to physical constitution of the soil; viz., from an excess of 
water in heavy soils. Here is found also souring of seed, which, to be sure, 
can occur also in light soils, but has been obserx^ed usually only in heavy, 
tough soils. 

The souring is due to a decay of the roots which have been longer 
in contact with standing water, charged with organic substances. Most roots 



1 Johannsen, W., Studier over Planternes periodiske Livs vttringer, I; cit. Bot. 
Jahresb. 1897, I, p. 143. 

2 Hiltner, L., in Prakt. Blatter f. Pflanzenbau u. Pflanzenchutz, 1903, Part I. 



202 

withstand very well a continued contact wuth running or standing water, 
which is free from organic substances, as can be seen in the different water 
cultures. Here, however, all living or dead vegetable particles in the culture 
vessels are avoided, for the decomposing organic substances take up all the 
oxygen which is present in a small supply. The roots of the growing plant 
must be killed because of a scarcity of oxygen and excess of carbon dioxid. 
Also, under ordinary conditions, seeds can survive contact with water, 
lasting for weeks, if the temperature is low. Thus Feige^ states that wheat 
which had stood for 5 weeks under cold water at 5°C. still lived. On the 
other hand, wheat kept 8 weeks under water, the temperature of which in- 
creased to 7°C. had disappeared without leaving a trace. Corn, which had 
previously been healthy, withstood water at 3°C. for 4 or 5 weeks, but was 
injured somewhat more than the wheat mentioned above. In the same way, 
alfalfa and clover withstood standing in water better than did com. 

According to Kiihn, rye suffers especially from souring, while under 
the same conditions brome grass and others develop very luxuriantly. To 
this circumstance is due the erroneous belief, which even now occasionally 
appears, that rye can change into brome grass. According to our view, 
"Arrabbiaticcio" of wheat in Marengo and on the Roman Campagna be- 
longs under this head. Peglion'- explains the disease as a general deteriora- 
tion of the plants due to being overrun by the luxuriant growth of weeds, 
w^hich thrive better than the wheat on unsuitable soil. In Southern Italy the 
disease is called "calda fredda" and "secca moUa." 

The souring of the winter oil seeds, especially rape, is the most serious 
of all. From standing continually in water the roots decay from the tips 
backward so that in spring only the crown of the root and the leaf rosette 
remain. These appear to be healthy as long as the moist spring weather 
prevents their dr}'ing out, yet, as the season becomes dry, the plants turn 
brown very soon and may be drawn from the soil by one leaf. 

An investigation by E. Freiberg and A. Mayer" serves to explain the 
fact that under continued wet conditions the character of the vegetation 
changes, so that phenomena appear like the above mentioned predominance 
of brome grass when rye had been sown. This experiment proved that the 
roots of marsh plants need much less oxygen than those of cultivated plants. 
This proves, as might have been supposed from the ver}^ beginning, that the 
individual plant species make different demands on the oxygen of the soil 
and, accordingly, must adjust their habitat to existing conditions. From the 
result of the experiments, however, another conclusion may be drawn 
which may serve in general when judging the demands made by different 
plants on soil; viz., the amount of air needed by their root systems. It 
is found that the more oxygen the plant needs for respiration, the greater is 
its nitrogen content. Marsh plants show a strikingly low nitrogen content and 

1 From Oesterr. landw. Wochenbl. cit. in Biedermann's Centralbl. 1877, p. 76. 

- Peglion, v., SuU' arrabbiaticcio e calda freddo. Annuar. d. R. Stazione di 
Patol. veget. Roma. Vol. I, 1901, p. 37. 

3 Freiberg, E, und Mayer, A., Ueber die Atmungsgrofse bei Sumpf- und Wasser- 
pflanzen. Landwirtsch. Versuchsstationen 1879, p. 463. 



203 

have an open inner structure, permitting the storing of larger quantities of 
air within the body and suggesting the facihtation of internal respiration. 
Real water plants respire with a lesser intensity than land plants, as Bohm^ 
found in his experiments, by measuring in a hydrogen atmosphere the car- 
bon dioxid given off during internal combustion. Since it may be assumed 
that the amount of respiration is determined by the amount of protein 
burned in the plant's body, the oxygen needed by the root system will be 
greatest in cultivated plants, rich in nitrogen, and the most suitable soils 
will be those which most completely satisfy this need together with the 
other demands of the plant, i. e., rich field soil, which is loose or has been 
loosened. 

Those lands, therefore, which are repeatedly subjected to an oxygen 
scarcity, through the formation of crusts from rain action and the deposition 
of silt by floods, will have to be improved by corresponding changes in their 
physical structure. In the cases of souring, on the other hand, in which the 
air supply is not necessarily cut oft' by the physical constitution of the soil 
and in which only an excessive supply of water can fill the large interstices 
in the soil, we will have to turn to the removal of the water.. Here deep 
drainage or at least drainage canals 120 cm. deep, lowering the ground 
water level by this amount, are the most advisable precautionary regulations. 
The development of so deep a pervious layer is necessary because many 
Leguminoseae, like alfalfa, and sainfoin, with their deep growing main 
roots and fewer fibrous roots, are apt to die when they reach the ground 
water. 

Souring of Potted Plants. 

The souring of potted plants occurs chiefly when loamy or peaty soils 
are used. If the drainage hole of the flower pot is stopped up and excessive 
amounts of water given by some inexperienced laborer, the roots of the 
potted plants die completely, since they become brown and soft. 

The sour soil can be recognized at once by its characteristic odor. In 
this the process of decomposition of the abundantly present organic frag- 
ments, always contained in nutritive pot soils, takes place very differently. 
Probably acid compounds and also free acids are produced from the but 
imperfectly understood humus elements. If iron is present in the soil the 
tminjurious ferric salts can be reduced to the injurious ferrous ones, since, 
when the soil spaces are enlarged with water, a perceptible scarcity of 
oxygen must occur. 

The water is saturated with carbon dioxid from the secretions of the 
roots and also from the decomposition of the organic matters in the soil, 
and, with continued action, the carbon dioxid is sufficient to kill the plants. 
W. Wolf- proved experimentally that healthy plants, set in water contain- 
ing carbon dioxid, at once began to eliminate it in very greatly reduced 
quantities. The result is a wilting of the leaves which die later. 

1 Bohm, Ueber die Respiration von Wasserpflanzen, Sitzungsber d. Kais. Akad. 
d. Wiss. zu Wien. 1875, May Number. 

2 Tagebl. d. Naturf. Vers, zu Leipzig 1872, p. 209. 



^o4 

£ven if we cannot yet explain with certainty the mechanics of wilting 
which take place here (the explanation given by W. Wolf^ does not 
seem to be sufficient) we will, however, scarcely go astray in assuming 
that, as the result of the excessive accumulation of carbon dioxid in the soil 
water, the normal elimination by the roots of carbon dioxid, which is con- 
siderable in vigorously growing plants, is at once arrested. An unusually 
high gas pressure must therefore be produced within the plant, increasing 
to a positive pressure in the ducts and reducing their ability to conduct 
water to the aerial parts. The power of the ducts to conduct water will be 
decreased by the amount taken up by the negative pressure in the ducts. If 
thereby this conduction of water is weakened without corresponding re- 
duction of the use of water in the leaves, wilting results immediately. If 
the plants are placed in distilled water, as in Wolf's experiments, a normal 
appearance and normal functions again set in. The distilled water in this 
case is like a sponge, absorbing the carbon dioxid and other excretory pro- 
ducts of the roots. 

Finally the result is the same for the root, whether the carbon dioxid 
appears dissolved in water, or as a gas resulting from an insufficient soil 
absorption. For the aerial parts of the plant, however, conditions are differ- 
ent and it is very important whether they come in contact with water rich 
in carbon dioxid or in air containing the gas. At least Bohm's experiments- 
on the leaves of green land plants have emphasized this. He immersed 
leaves of different land plants under water containing carbon dioxid and 
found that the plant no longer gave oft' oxygen if the part concerned was 
prevented from surrounding itself with an atmosphere containing carbon 
dioxid which would cut it off from direct contact with the water. 

The results of excessive watering in pots with the drainage stopped 
and the consequent cessation of plant and soil activity are best determined 
by a microscopic comparison with the soil in a pot containing a healthy 
growing plant. What intense activity is found in the soil ! From the upper 
surface down to the bottom of the pot (in leaf and heath earth) are found 
fragments of leaves and stems, on which many kinds of the so-called mold 
forms with sterile mycelia, or with mature conidia, exercise their power of 
decomposition. According to the nature of the vegetable matter, Sepedon- 
ium (chrysospermumf), V erticillium ruherrimum, or P enicillium glaucum, 
Acremonium, Acrocylindrium, Cladosporium penicillioides, dift'erent kinds 
of Fusiarium and many others are found. On the upper surface often still 
other genera occur, especially the aerobic ones together with living diatoms 
and other forms of algae. The schizomycetes go deepest of all. Starch 
granules and bits of cytoplasm are found surrounded by colonies of rod 
bacteria radially arranged; colonies of bacteria have often been established 
also on fragments of crystals. All this active life is engaged in reducing 
the plant substance and favors the processes requiring oxygen, which we 



1 Jahresber. f. Agrik.-Chemie, 1870-72, II, p. 134. 

2 Anzeigen der Wien. Akad. d. Wiss., 1872, Nos. 24-25, p. 163. 



205 

term decomposition. All this active life will either be stopped, by closing 
the soil interstices with water, or be turned to those destructive phenomena 
of decay, decomposition in the absence of oxygen. Every soil has its my- 
cological as well as its bacterial flora, which decomposes the organic sub- 
stances. According to Oudemans and Koning^, these are approximately 
typical for definite kinds of soil. 

In potted plants it is safe to assume the beginning of stagnation when 
the upper surface of the soil is covered with a hard white or reddish colored 
lime crust, firmly attached to the edge of the pot. From the uncommonly 
large amount of carbon dioxid developed by the addition of acetic acid, 
it is evident that the incrustation of the uppermost soil layers in the pot, 
and at the edges, results especially from calcium carbonate. 

Magnesium carbonate is met with and also ferrous carbonate, which 
later through oxidation, produces as ferric hydrate dififerent colors in the 
crust. According to the microscopic examination, the characteristic 
swallow-tailed crs^stals of gypsum and the octahedrons of calcium oxalate, 
as well as the rhombic forms of calcium phosphate, soluble in acetic acid, 
occur. The presence of the last named salt can not always be demonstrated 
and never in large amounts. On the other hand, calcium carbonate and 
probably magnesium carbonate, together with very fine particles of quartz 
sand, make up the usual substances of the crusts, between which is per- 
ceptible at first an abundant fungous growth with a formation of conidia on 
the humus. The production of these crusts may be explained by the fact 
that the water, given in large quantities in watering, becomes charged with 
the carbon dioxid, abundantly produced by the process of decomposition 
within the soil interstices. Hence water is a splendid medium for dissolving 
the calcium carbonate present in the soil, the magnesia, the ferric phosphate, 
the ferric silicate, etc. 

The more quickly the superfluous water is drawn away by good drain- 
age in the pot, the less will the minerals be dissolved and washed away. On 
the other hand, if the water stands in the pot and once becomes charged 
with calcium, which is soluble in the form of calcium bi-carbonate, it can 
only be removed by evaporation from the saturated upper surface of the 
pot and, w^hen the pores of the pot are not closed by a green, slimy algal 
growth, this excessive water also evaporates slowly through its sides ; it 
leaves behind the dissolved substances. The pots "become coated." The 
calcium remains behind as calcium carbonate just as on the edge of a kettle 
in which water containing lime has been boiled. 

Thus the usefulness of the two processes, the frequent washing of the 
flower pots and the breaking up of the upper surface of the soil, is dem- 
onstrated. 

In the increasing desire to attain our ends by fertilization, different 
fertilizers are added to water soaked plants, but the main need, — sufficient 

1 Oudemans, C. A. J., et Koning-, C. ,T., Prodrome d'une flora mycolog-ique obtenue 
de la terre humeuse du Spanderswoud etc. Extr. Archiv. neerland. ; cit. Z. f. Pflan- 
zenkr. 1903, p. 60. 



206 

aeration of the soil, — is overlooked. The plants have not improved with this 
treatment. The best results are obtained by transplanting when growth 
starts and the application of heat to the roots to stimulate growth. 

Eichhorn's^ investigations prove that fertilizing may be injurious rather 
than advantageous with acid soil, in the presence of free humus acid. He 
states that earths, rich in humus, which contained free humus acid, liberate 
the acids from solutions of neutral salts. The acidification thus produced 
is stronger than it would be without these salts and, therefore, fertilization 
with neutral salts will increase the acid in such soils. This happens with 
calcium phosphate or any phosphate where the phosphoric acid, or calcium 
phosphate, passes over into solution. The addition of neutral potassium 
salts, especially alkaline sulfates, favors decomposition. If tlie humus 
acid is combined with a base, such acidification does not take place. The 
addition of manure, liquid manure, etc., will act only disadvantageously 
with such chemical decomposition and is to be avoided as are marly earths. 

Injudicious Watering. 

The frequent dying of house plants makes necessary a reference to in- 
judicious watering. Excessive watering may be due to the fact that in- 
experienced people assume a lack of moisture in the soil as soon as the plant 
wilts. The fact that frequently, after watering, the plant becomes turgid 
during the course of the day gives weight to this assumption. If wilting 
follows this second turgidity, water is added until the plant is permanently 
wilted and the roots decay. Such conditions arise especially in the autumn 
when the more tender plants are put in conservatories with but little heat. 
The coldness of the soil then causes the wilting. We know from a number of 
cases cited by Sachs- that dififerent plants require definite temperatures for 
their roots to keep them working, i. e., taking up water. Tobacco and 
pumpkins wilt in a soil at 3° to 5°C. ; but if the same soil is warmed to 
12° to i8°C., the root activity is re-established. In the examples cited above, 
when the previously watered, wilted plants become turgid during the day, 
this result is attributed to the influence of the watering. The real cause, 
however, was the diurnal rise in temperature of the air and of the soil, 
caused by the sun, whereby the roots were again stimulated to take up 
water. W^ith the coming of night and the corresponding fall in temperature 
below the limit at which the roots are still to take up water, the wilting is 
repeated. The plant can therefore die of thirst even when the soil is very 
moist, if the soil be too cold. On the other hand, in moist air, the plants 
can remain alive a long time with wholly decayed roots, as is shown by water 
cultures. This is also the reason wh)% in root diseases, symptoms of dis- 
turbance are noticeable in the aerial organs only at a late stage. 

Another cause of the wilting becomes noticeable in midsummer. If 
plants transpiring rapidly are exposed for some time to the hot sun and to 



1 Landwirtsch, .TahrbiJcher 1877, p. 957. 

2 Lehrbuch der Botanik, 1st. Ed., p. 559. 



20/ 

currents of air, they begin to wilt in spite of sufficient soil moisture, because 
the quantity of water evaporating through the leaves cannot be replaced 
quickly enough by the root. To be sure, the supply of water will be in- 
creased as the temperature rises simultaneously with the increased sunshine. 
According to De Vries\, imbibition of the cell walls is increased and thereby 
their ability to conduct water, but the increased supply, nevertheless, cannot 
make good the loss through evaporation and the leaves must droop. If the 
pots are then watered, w'ithout having been tested, the earth will become 
sour. 

The same result is found in the so-called New Holland and Cape plants 
belonging to the families of the Epacrideae, Ericaceae, Papilionaceae, 
Rutaceae, etc. The loose, fine, sandy, but little decomposed earth, such as 
heath mould, cannot be pressed very firm into the pots, because the unde- 
composed pieces of roots and leaves form a very loose consistency ; with too 
heavy watering, however, the fine grains of sand and clay are first stirred 
up and then washed down so that only the long, loose fibrous elements re- 
main at the upper surface of the pot. These naturally retain but very little 
water and let it run down very quickly to the bottom of the pot. On this 
account the upper surface of the pot is always almost half dry. If now the 
gardener lets himself be led astray and waters the pots under such con- 
ditions, and if the pots have no good drainage, the very fine roots will decay. 
(It should be remarked in passing, that the so-called soured pots quite fre- 
quently show an alkaline reaction. I found with potted plants, whose roots 
had decayed, that moist red litmus paper turned blue as far as it lay upon 
the surface of the pot). 

As a means of overcoming this, transplanting into very sandy earth and 
sinking the soured plants in beds with warm soil has already been recom- 
mended. As a matter of course the roots must be cut back to the healthy part 
when transplanted. As a precautionary measure, the pots may be plunged into 
the ground and similar methods may be recommended. In doing this, how- 
ever, a stick or a piece of wood, turned like a cone, should be used to make a 
deep, funnel-like hole, whose upper edge is exactly the size of the edge of 
the pot. The pot then hangs in the hole. Below the pot the lower part of 
the conical hole forms a cavity and prevents the earth worms from crawling 
into the drainage hole in the pot and stopping it up. In flower pots stand- 
ing in a room, or on flower racks, the soil will not sour if only some little 
care is taken. The water content of the soil may be judged easily and com- 
paratively accurately by tapping the pot. If the earth is full of moisture, 
the water lies between the individual particles of soil and the sides of the 
pot and the sound resembles that of a dense mass ; when the amount of water 
is scanty, however, the pot rings hollow. 

According to the above, therefore, one should consider not only how 
much to water, but in what way potted plants should be watered. In order 
to avoid washing away the finest particles of clay and sand and thereby 



I Bot. Zeitung-. 1872, p. 781. 



208 

forming crusts, or choking the drainage of the pot, the water should never 
he poured quickly through the spout of the watering pot. In plants set in 
pots and sunken, a hose should be used, or, in pots set on forms in con- 
servatories, a slender and long spout, giving only a gentle stream of water. 
One should avoid holding the stream of water at the base of the stem, 
which is often entirely white as a result of incrustations of lime. 

Use of Saucers Under Pots. 

In house plants the use of saucers under pots is general. This saucer 
is necessary for preserving cleanliness on the window sill and on the flower 
table, but is usually injurious for the plants themselves. No matter whether 
the pots be watered from above or by soaking up water from the saucers, 
the soil will almost always take up too much water. Many plant lovers con- 
sider this condition advantageous. The result, however, is a choking of the 
roots at the bottom of the flower pot. The decay of the roots continues 
gradually upward and finally shows itself in the dying of the edges of the 
leaves. If these symptoms appear, the plant is, as a rule, lost to the ama- 
teur, but the gardener can often cure it. For the amateur, who has no 
warm bed at his disposal, we would recommend setting the sick plant in pure 
sand and placing it in a warm, half shady place. 

The Running out of Potatoes. 

In discussing the disadvantages of heavy soils, we should consider the 
point of view, repeatedly brought forward in practical circles, that our 
potatoes "run out," i. e., gradually lose their good qualities and degenerate. 
Some people would explain this by holding that, in the customary method 
of propagation by planting tubers, one really propagates asexually, without 
interruption, an individual once produced from seed and that, thereby, an 
organism so long lived must at last .show the weakened condition of old 
age. A proof of this is found in the retrogression in the starch content of 
our favorite older varieties as, for example, in the Daber potato. 

According to our point of view, the cause of the supposed running out 
lies in the lack of foresight of the agriculturalist in growing varieties on 
heavy soil which have been produced on light soil. 

We refer in this connection to Ehrenberg's work^ on the results of 15 
years experiments at the "Deutsche Kartoffelkulturstation." The average 
yield of all the varieties grown seemed to increase constantly from 1889 to 
1903. In regard to the "Daber" potato, the yields decreased only on heavy 
soil which is easily explained since in Daber a very light, dry, sandy soil 
predominates. If newly grown seed of this variety was planted in heavy 
close soil, it gave better results than the form which had been cultivated there 
for some time. The same new seed, however, planted in sandy soil, usually 
gave a poorer result when compared with the naturalized plant. We find 



1 Ehrenberg, B., Der Abbau der Kartoffeln. Landw. Jahrb, Vol. XXXIII; cit. 
Centralbl. f. Agrikulturchemie, 1905, p. 235. 



PART III. 



MANUAL 



OF 



Plant Diseases 



BY 



PROF. DR. PAUL SORAUER 



Third Edition—Prof. Dr. Sorauer 

In Collaboration with 

Prof. Dr. G. Lindau And Dr. L. Reh 

Private Docent at the University Assistant in the Museum of Natural His'.ory 

of Berlin in Hamburg 



TRANSLATED BY FRANCES DORRANGE 



Volume I 
NON-PARASITIG DISEASES 

•BY 

PROF. DR. PAUL SORAUER 

BERLIN 



> WITH 208 ILLUSTRATIONS IN THE TEXT 



•i-e'-v 



9.^ 



Copyrighted, 1915 

By 

FRANCES DORRANCE 



©CI.A401.187 

THE RECORD PRESS 
Wilkes -Barre, Pa. 



MAY 29 1915 



209 

proof in these experiments that newly introduced seed retains at first the char- 
acter developed in the place where it has been bred. If, for instance, heavy 
soil reduces the starch content, the reduction does not take place in the first 
year with new seed and therefore this seed contains more starch than the 
native seed. On sandy soil, however, a variety has been bred which contained 
the largest amount of starch possible under the conditions. The newly intro- 
duced varieties with the peculiarities brought with them, however, had not 
as yet adjusted themselves sufficiently to these conditions and therefore gave 
a lesser yield. Exhaustion or degeneration will therefore take place only 
where a variety does not find the cultural conditions it requires. The cir- 
cumstances may be similar in all phenomena of supposed exhaustion or 
degeneration. Our cultural varieties are the products of breeding under 
very definite conditions of position, soil and weather, and are kept pure only 
if they again find conditions similar to those where they are grown. If it is 
desirable to make use of valuable peculiarities of any definite species in 
another locality, good results are obtained only by frequently renewing with 
seed from the native habitat or from habitats similarly situated. 

Sensitiveness of the Sweet Cherry. 

The complaint in different places that the sweet cherry every year suf- 
fers increasing injury from frost, the exudation of gum, attacks of fungi 
etc. is often due to the failure to observe the fact that the cherry does not 
like a heavy soil. This circumstance has been especially emphasized recently 
by Ewert^ and deserves to be repeatedly borne in mind by the fruit breeder. 
Naturally here also some cultural varieties are able to adapt themselves 
better to heavier soils, but in general the rule holds good that the sweet 
cherry likes a light, deep soil and flourishes especially well on alluvial sand 
and loose soils. The amount of nutrition in the soil is a far less decisive 
factor than its physical constitution, especially its granular condition. 

Often a scarcity of lime is given as the cause of poor growth, > which 
can be overcome by supplying lime. The improvement in growth, however, 
may not always be traced back to the nutritive action of the lime but to the 
change in the physical soil condition due to it, viz., greater friability and 
thereby increased aeration. Ewert's statements throw light on lime as a nutri- 
tive substance. He states that the sweet cherry flourishes even when the lime 
content is from 0.04 to 0.15 per cent. Soil with possibly 80 per cent, of 
easily washed away particles is not suited to the growth of cherries even 
with 40 to 45 per cent. CaCOg, if this is chiefly present in so fine a condition 
that it also can be washed away. The cherry is peculiarly sensitive to stand- 
ing water and it grows best in dry soil in open places. 

The Tan Disease. 
Trees standing on damp ground may show decreased growth, especially 
if their early growth was rapid. The older bark cracks or, after the outer- 

1 Ewert, Das Gedeihen der Stifskirschen auf einigen in Oberschlesien hauflgen 
Bodenarten. Landw. Jahrb. 1902, Vol. XXXI, p. 129. 



210 



most cork layers have fallen off, blister-like or flat, warty swellings put in an 
appearance and later these have a diseased wooly outer surface. If the 
place becomes somewhat dry, a reddish yellow to a brownish yellow powder 
may be brushed off which in color resembles fresh tan bark. This may have 
given rise to the term "Tan Disease." In introducing the subject of this dis- 
ease into scientific discussion I have re- 
tained the name used by practical growers. 

The same process takes place also in 
roots and young branches. Young bran- 
ches with knotty tan pustules may be 
found in cherries. Up to the present this 
disease of the bark of the older trunk and 
roots has been observed most frequently 
in apples. Plums seldom suffer. Similar 
processes, resulting in the falling off of 
larger pieces of bark, have been found in 
elms and will be treated under growth 
disturbance due to marshy soils. 

In figure 23 is seen a piece from an 
apple root, natural size. Its bark has been 
broken open by cross-tears varying in size, 
the edges of which have been forced back ; 
the open places are covered with an ochre 
powder or (when first taken from the soil) 
with soft, moist, brown masses. Figure 
24 represents a cross-section through such 
a callus place. We find the wood (c is the 
cambial zone) of a practically normal 
structure traversed by the medullary rays 
(m), most of which show no variation 
whatever. Only in some (m') it is notice- 
able that in the younger portions they be- 
gin to broaden, thereby causing a looser 
construction. This process of loosening, 
however, finds its evident expression only 
in the bark where the rows of medullary 
ray cells, beginning to separate from one 
another, form loops. While the younger 
inner bark, with its hard bast cords, still shows no change from a 
normal structure, the older layers (at left side of the illustration) display 
an impoverishment of the cell contents and some radial stretching (k'). 
This excessive elongation of the bark parenchyma becomes greater, the fur- 
ther toward the outside the cells lie, and it increases within the cork zone in 
such a way that the cells lying free on the outer surface take on a pouch- 
like form (s) and are only very loosely united with one another. 




Fig-. 23. Apple root with ruptured 
tan spots, natural size. (Orig.) 



^It 



If the outer surface of the root dries off, the cell pouches shrink and, 
in the outer layers, are entirely separated from one another. Then a tan- 
colored, powdery mass forms which may be wiped away with the finger. 
Even the lamellae of plate cork (t) which are present at the edge in thick 
layers (of equal size, under normal conditions) and, graduall}^ dying back 
from the outside, fall away at the place of the tan disease, are also drawn 
into the process of loosening. These split off because some of the middle 
layers round off their cells and show a tendency to assume the structure of 
cork as will be described more fully later under the cherry. 




Fig. 24. 



Cross-section through a diseased spot in an apple root. (Tan disease.) 

(Orig.) 



If the outgrowth of the bark at the edge of the tan canker and the emp- 
tying of the cell have reached maturity, the well-known hourglass arrange- 
ment of plate cork layers occurs (f) which cut off the hypertrophied bark 
parenchyma, finally becoming cork, and it becomes an element of the bark 
scales. The cell elongation meantime advances laterally and further toward 
the inside. Thus at w we see the beginnings of this since the bark cells, 
normally elongated tangentially, are becoming square in cross-section and in- 
crease in number by division in order to round off more toward the diseased 
side, to become more open by enlargement of the intercellular spaces (r) 
and finally to pass over into the radial elongation which increases to pouch- 



212 



like outgrowths. By this advance of the process of over-elongation 
into constantly younger bark parenchyma layers, the activity of the root is 
finally exhausted at the place of the tan disease. 

The injury is not so intensive in the aerial axes Sometimes in larger 
trunks the phenomenon is not noticed until the bark is closely examined. It 
is then found that some bark scales stand out raggedly. If these are re- 
moved, which may be done very easily, it is observed that the outermost 
layers of the succulent bark tissue form irregular blister-like swellings which 

rupture later and decompose into dust-like 
masses which may be wiped away in dry 
weather. Figure 25 shows the fresh bark sur- 
face of an apple tree which has been laid bare 
by the removal of the outer bark scales. 

On this greenish brown, juicy surface 
hemispherical or elongated warty excrescences 
(a) appear very clearly. Figure 26 shows a 
cross-section through such a boil-like swelling 
in which, however, the wood, cambium and 
youngest inner bark have not been drawn. 
We recognize at the first glance the corres- 
pondence in structure with that of the tan spot 
of the root. At the lower part of the figure 
we find the bark parenchyma with three hard 
bast bundles of a normal arrangement and 
position, but close above these hard bast bun- 
dles is noticeable a change in position since 
the tangentially elongated bark cells, rich in 
chlorophyll, begin to increase in length radially 
(r), to divide and to be arranged in parallel 
lines broken by large intercellular spaces (i). 
The fact that this change in tissue must have 
taken place very early, at the time of pushing 
out from the cambium, is evident because the 
permanent tissue of the coUenchyma (cl) has 
developed only one layer within the tissue of 
the excrescence. The chief part of the swelling has come from the peri- 
pheral layers which have developed into ctishions (zv) of elongated, finally 
pouched cells (s), which have raised the plate-cork cell layers and finally 
split them. 

In explaining this phenomenon we must not forget that these tan places 
arise underneath the old bark scales, and, with a formation of full cork, finally 
become bark scales by suberization. Thus we find that the organization of the 
bark into constricted and constricting cell layers, as they alternate in the 
bark, has taken place in the young bark tissue, for we find that, in young 
fresh bark tissue, cross bands of plate-like cells, varying in structure and the 




Fig. 25. Piece of the bark 
from the trunk of an apple 
tree with the tan disease. 

a the calluses of the tan disease, b frag- 
ments of the dry bark scales covering 
the whole. (Orig.) 



213 

constitution of their walls, transverse in curves (np) the hypertrophied tis- 
sue, which, at the beginning, contains starch. 

This formal and functional organization of the bark parenchyma which 
determines the formation of the bark may be found also in other tree barks, 
but first occurs, so far as I have observed, in the older axes in which the 
bark parenchyma has been influenced by the pressure of the bark scales 
lying above it. On this account I have called these bands of tangential cells 

s 




Fig-. 26. 



Spot on the trunk of an apple tree with the tan disease, 
the letters in the text. (Orig.) 



Explanation of 



(np) "Pressure bands," which later suberize, often also developing plate 
cork cells and cutting off the bark scales. 

I have had opportunity to study the tan disease in young cherry branches 
in a wet summer on very vigorous young trees in a nursery. Figure 2y 
shows that on these cherry branches the outer bark had split or been torn 
open in broad, irregular stripes (e). An intense yellow ochre colored mass' 
(/) could be recognized at the ruptured spot, which, when tapped vigorously, 
gave off a powdery dust. The whole impression given by these branches 
was as if they had been very thickly covered with rust fungus. 



214 



The first indication of the disease occurred in July, when, among nor- 
mally growing trunks, the leaves of some specimens turned yellow and fell 
off. Nevertheless the terminal buds of the branches developed a vigorous 
August growth which held most of its foliage until fall. In September the 

outer bark covering split and the 
surface appeared like yellow ochre 
velvet beginning at the lowest part 
of the branch and decreasing in in- 
tensity toward the tip. Further, 
the fact is worthy of notice that 
practically only the luxuriantly 
growing wild trees appeared to be 
diseased. The phenomena of the 
tan were only sparsely noticeable in 
grafted trees. It was seen at once 
that branches, where they had re- 
tained their leaves, had only a few 
really torn spots in the bark, indeed 
only closed, warty excrescences, i. e. 
the younger stages of the disease. 
In the axils of two year and much 
older diseased trees, ruptured places 
in the bark (r) occurred less fre- 
quently. Usually the individual 
■^ centres of disease appeared there 
in the form of ver}'- broad, very 
high yellow ochre cushions running 
crosswise. 

The investigation of these cus- 
hions and of the broad, ruptured, 
discolored surfaces on branches one 
year old showed at once marked 
correspondence with those on the 
older ones ; only it could not be 
seen that the lenticel cushions give 
off any dust. The discolored mas- 
ses were found to be light brown, 
cylindrical, wrinkled cork cells with 
rounded corners, which were broken 
off individually or in small groups. 
The branches, giving off this dust, seem with a few exceptions to be 
otherwise healthy, only their primary bark is very much broken by the 
considerable separation of the parenchyma cells. Places with loosened 
structure are found in the wood as well as in the bark. Cross bands of duct- 
less parenchyma wood may be noticed in the stages produced toward the 




Fig-. 27. One year old and two year 
old cherry branches with tan cushions 
between the split bark stripes. (Orig.) 



215 

middle of summer. These are filled full of starch, while the normally 
constructed wood, excepting the medullary rays, has none. Within these 
cross bands the medullary rays are broadened and have gummy spots. 

The beginnings of the tan formation are found close under the terminal 
buds of the topmost branches, where the epidermis is still uninjured, but is 
already underlaid with cork, possibly five layers thick. In places, this pro- 
tective layer, consisting of comparatively thick walled cells, corresponding 
to plate-cork, shows a change even in its first stages, so that the cells lying 
directly beneath the epidermis have developed into parallel rows of cylindri- 
cal, radially elongated; brown-walled, full-cork cells. There is present here, 
therefore, the character of lenticel growth which StahU has already de- 
scribed thoroughly for the cherry and which only differs from his descrip- 
tion in that here the full cork cushions are rarely produced under the 
stomata. 

It is seen that an extensive formation of full cork can take place in- 
dependently of the stomata in the development of a plate-cork layer, since 
several layers of lenticels are produced in which the cork formation ad- 
vances inward into the primary and, in fact, into the secondary bark. 

As the shoot of the current year becomes older, a second layer of plate- 
cork appears very normally, directly beneath the one first produced. It has 
been found just as thick (viz., 5 to 7 cells) as the first whose cells gradually 
collapse with the apparently lessened swelling and the browning of the walls. 
During this process the normal cork covering of the cherry trunk appears 
to be differentiated into two layers. The upper, older one is very dense, 
since the cells usually have so collapsed that their cavities are recognizable 
only as fine lines; this layer passes over gradually into the second, later 
formed cork layer. In the latter, the plate-like cells are very uniform and 
their wide lumina are filled wath a watery content or even with air. They 
border on a browned cell layer, with a clearly protoplasmic w^all lining, 
which, as cork cambium, assumes the continued formation of the cork layer 
occurring in places. When treated with sulfuric acid, the composition of 
the oldest, sunken, collapsed brown cork layer is easily recognizable, since 
the cells are often distended and show in places their original height and 
width, at times almost square in cross-section, while the full cork cells are 
not changed. With this treatment the layer, produced later, rounds out its 
youngest cork- cells into hemispheres after the cork cambium has been 
destroyed. 

In the formation of the many layers of lenticels, the development of 
such elements is repeated in the secondary cork layer underneath the first 
centres of full cork. 

The second case of lenticel formation, not connected with stomata, is 
illustrated in figure 28. This shows the cross-section of a new structure on 



1 Stahl, Entwicklungsgeschichte und Anatomie der Lenticelle. Bot. Z. 1873, 
No. 36. 



2l6 

the barked cherry trunk. We must imagine that all the tissue here shown 
in the form of a callus covered with bark rests upon the old wood cylinder 
from which the bark has been removed. 

Since reference to the anatomical processes, leading to the formation of 
this new tissue on the exposed wood, is made in the chapter "Wounds" 
(bark wounds), we will mention here only the fact that, if at any given time 
the bark is removed from a tree, the newest cambium, thus exposed, begins 
to grow again and covers the wounded surface with a parenchymatous tissue 
layer. This parenchymatous covering is increased by the later appearance 
of a constant meristematic layer. The inner surface of this layer forms 




-TSt 



Fig. 28. Newly formed wood and bark body on the bark wound of a cherry trunk. 
The bark shows a lenticel excrescence. (Orig'.) 

normal cambium, which gives rise to woody tissues toward the centre and 
back towards the periphery. 

Figure 28 is a new structure several months old which, in the form of a 
broad wrinkled callus, has grown on the cambium of an experimentally 
barked sweet cherry trunk. The old wood of the barked trunk has been 
omitted in the drawing; it would join on at hp. The cambial zone (c) 
has sharply differentiated this tissue into wood and bark. The wood, where 
it rests on the old trunk, has a parenchymatous structure (hp) ; which later 
passes over into a vascular new wood (nh) forming libriform fibres. The 
structure of the bark is at first irregular and corresponds to the formation 
of wood which only gradually obtains its normal structure, for the hard 



bast bodies begin in the form of individual, short elements {hh) with wide 
lumina and only later grow out from the cambium as connected groups of 
elements {hh^) elongated like fibres^. 

The bark of the new structure has formed a protective cork layer in 
its peripheral parenchymatous layers which has gradually grown very thick. 
At first only plate cork was formed ; but later, in different places, full-cork 
masses {Ik) developed instead of the plate cork cells, splitting the covering 
{k) composed of the latter cells and pressing the cork cambium inward {kk) 
by their increase which extends further and further backward. 

The full cork began to form when the whole peeled surface, for the 
purpose of further investigation, was enclosed in a glass cylinder, partly 
filled with water. While this lenticel out-growth, produced from the phello- 
gen, was only slightly noticeable in those parts of the bark which remained 
in the air, it had developed an unusual luxuriance below the surface of the 
water. 

The tan disease of the cherry is therefore an abnormal increase of the 
normal lenticel formation. So many and such extensive full-cork cushions 
are produced close to one another that they unite, pushing off the epidermis 
in large connected tatters and appearing as uniform velvety surfaces cover- 
ing a large part of the branch. The outermost layers of the full cork cush- 
ions are so loose that the connection between the peripheral cells is broken 
by a slight blow when the air is dry ; this explains the discoloration and the 
dust flying from places affected with the tan disease, if the spots be touched 
or shaken vigorously. This scattering of the dust increases with the num- 
ber of full cork cells lying above one another and cushions composed of 
parallel rows of full cork, 20 cells deep, have been observed. In this case 
the process of elongation has included the entire thickness of the primary 
phelloderm so that the later formed, secondary full cork lies directly under- 
neath this, i. e., no separating plate cork layer is left between the different 
generations. 

The appearance of the tan disease will have to be traced to the super- 
abundance of water in the hark body. This local excess of water may be 
due, on the one hand, to supplying the roots abundantly with water, especially 



1 Reference should be made in passing to the illustration of the beginnings of 
tuber gnarls not in any way whatever connected with the tan disease but shown 
in the drawing- at B. They are produced by a local accumulation of plastic material 
as, for example, the isolated wood in the bark of the new structures formed near 
the wounds of various trees (cherry, apple, pear and pine). At the centre of such 
wood formations with a spherical wart-like structure may be recognized one or 
more hard bast cells. 

The case in which hard bast cells (especially diseased ones) are overgrown by 
tissue is of very frequent occurrence in injuries of very different origin. This over- 
growth consists usually only of a covering of plate-like cork cells several layers 
thick. In some cases, however, instead of the rapidly transformed cork cambium, 
a persistently active cambial layer is formed which deposits wood elements toward 
the inside and bark elements toward the outside. Such a case is represented in the 
wart-like tissue excrescence (B) at (u') while at (u) in the left part of the figure 
(A) may be seen only a cork covering around one of the isolated hard bast cells 
first produced. The bark rays pass around these new structures on both sides as if 
around some foreign body. 



2l8 

those of vigorous individuals ; on the other, by the lessened transpiration of 
the bark because of greater humidity. Such conditions in the cherry lead 
to lenticel excrescences as is proved by experimentally producing an accum- 
ulation of full cork in parts of the bark kept under water and further by 
observing specimens naturally diseased. In this way it was discovered that 
the cork excrescences preferred the youngest, well-leaved internodes in 
which the bark formed folds. Such folds were produced, for example, in 
places where the vascular bundles of the leaf left the axial cylinder and 
pushed out the bark when passing into the petioles. 

Some other observations have been made showing that the decreased 
evaporation due to increased moisture favors lenticel formation. Thus 
Stapf ^, in his studies on the potato, mentions that stomata develop into lenti- 
cels if transpiration is arrested. Further, Haberlandt^ found that in the 
horizontal branches of different trees (the linden, elm, honey locust, etc.) 
the lenticels always occurred in greater numbers on the under side than on 
the upper side, although counting the stomata on both sides gave approxi- 
mately equal numbers. The under side of the branch, inclined toward the 
earth, will surely transpire less than the upper side, because of the greater 
proximity of the soil and the lesser supply of air. 

The tan cushions in plum trees are essentially similar to those observed 
in the cherry. As yet they have been observed only on old specimens with 
diseased roots. I have known of only the initial stages in apricots. In all 
varieties of stone fruits the cork excrescences were accompanied by marked 
processes of bark loosening which in part resulted in the shoving of the 
bast cords towards the outside. In young wood a weakly developed wood 
ring and a reduction of hard bast bundles to isolated wide bast cells, filled 
with a brownish-red gummy substance, w^as often noticed where the tan 
disease had not broken out. Traces of gummosis were present everywhere, 
and at times rich gum centres were found. In cherries, the especial sus- 
ceptibility of certain varieties to the tan disease may be recognized when 
different varieties are planted close to one another, as, for example, in the 
"black ox heart" and in "Winkler's white ox heart." 

All the cases which I have known originated on heavy soils or marshy 
meadows. The history of some cases showed that the diseased trees had 
been fertilized with stable manure or liquid manure. These statements in 
connection with the anatomical conditions lead me to explain the tan dis- 
ease as the result of an excessive w^ater supply from the soil. When trees 
are attacked during vigorous growth, they undergo such a disturbance that 
the evaporation from the top is not sufficient to remove the excess of water. 
The decreased leaf activity, or a partial loss of foliage due to atmospheric 
influences or to pruning, should receive especial consideration. These cork 



1 Stapf, Beitrage zur Kenntnis des Einflusses geanderter Vegetationsbedingun- 
gen etc. Verh. d. Zool-Bot. Ges. Wien; cit. Bot. Jahresb., VI. Jahrg., Section I, p. 214. 

2 Haberlandt, Beitrage zur Kenntnis der Lenticellen. Sitzungsber. d. Akad. 
d. Wiss. in Wien, Vol. LXXII, Section I. July No. 1875. 



219 

excrescences and phenomena of loosening of bark and wood occur also in 
healthy trees, with corresponding conditions in the place of growth, but in- 
crease in the tan disease to an extreme manifestation. 

The remedies are apparent, and extensive aeration of the soil chiefly 
promises success. 

The Girdling of the Red Beech. 

According to the description given by Th. Hartig^ the disease named 
in this heading, which I have not known from my own observation, should 
be included here. Hartig found in a beech grove, 20 years old, that many 
trunks, beginning about one to two metres above the ground and extending 
to the top of the tree, were surrounded at intervals of 30 to 100 cm. with an 
almost circular, somewhat spirally running roll as thick as a quill. These 
rolls were proved to be overgrowth phenomena in wounds caused originally 
by lenticel excrescences. The formation of cork had extended further and 
further backward into the bark until it reached the wood and for a year or 
two years the formation of wood was arrested at this point. No appreciable 
injury due to the disease, which occurs only in very well grown sapling 
groups and there especially on trunks of the first or second class, could be 
confirmed. 

Root Disease of the True Chestnut (Mai nero). 

This disease, very common in France, manifests itself, according to 
Delacroix-, most strikingly in damp, impenaous soil and in grafted trees. 
The leaves lose their dark green color and the branches begin to dry up at 
the tips. The nuts only partially ripen and remain in the burrs. Delacroix 
found that the mycorrhiza of the fine roots had changed, as if diseased, and 
had assumed, as he thinks, a parasitic character because the amount of 
humus was deficient. The mycelium then grows into the larger roots up to 
the base of the trunk and then, in the trunk, upward to the branches. A 
secretion containing tannic acid results from the injuries to the roots and 
trunk. In this weakened condition, the trees offer a suitable centre for in- 
fection by other parasites, as, for example, Polyporus sulfur eus and Armil- 
laria mellea as well as Sphaerella macidiformis. 

I include this disease at this point because of the results of a thorough 
investigation which I had an opportunity to make with material from Ren- 
nes. The explanatory letter sent by M. Crie stated that the dying branch- 
wood had an odor indicating fermentation if broken, or the bark removed, 
and he suspected a conversion of the tannin, whereby glucose and alcoholic 
fermentation took place. The pieces of branches sent were thickly covered 
with lichens and the leaves showed a browning which extended from the 
edge deep into the intercostal fields. 



1 Hartig, Th., Vollstandige Naturgeschichte der forstlichen Kulturpflanzen, p. 
211. Berlin 1852. 

2 Delacroix, G., La maladie des chataigniers en France. Bull soc. mycol. de 
France XIII, 1897, p. 242. 



220 

The roots decided the matter. They had a rough appearance due to a 
great many black, hard cushions, differing in size and flattened into hemi- 
spheres, which covered the upper surface. If treated with a solution of caustic 
potash, when the tannin, occurring as a flocculent precipitate, turned a wine 
red to hrown, cross-sections show that the bark excrescences were covered by 
a normal cork layer. The primary bark had developed parenchymatous ex- 
crescences the cells of which, arranged in radiating rows, had polorless walls, 
apparently dissolving with difficulty in sulfuric acid, and had a very firm 
brown content. These bark excrescences were later cut off by an hourglass- 
like, plate cork lamella, distending the outer cork layer, and were forced out 
over the upper surface of the root as calluses by the subsequent growth of 
the inner bark. The healthy bark was filled with starch. 

In the material sent me the branches had only very sHghtly raised bark 
excresences, possibly ^ to >^ mm. broad, flattened and hemispherical. In 
them was found the beginning of a many layered lenticel excrescence such 
as had been observed in great numbers in the cherry with the tan disease. 
The constitution of the leaves, still remaining on the branches, had already 
indicated the diseased condition of the roots. They showed a browning and 
drying up of the parenchyma in the intercostal fields, extending from the 
edge toward the mid-rib. Finally, the parenchyma was green only in the 
immediate proximity of the ribs. The black, yellow-edged, roundish spots, 
scattered over the sick leaves and containing various fungi colonies, must 
be considered as secondary phenomena. The condition found in the 
branches in connection with the excrescences on the roots brings the disease, 
which has been termed "Mai nero," into the group of the tan diseases. Ac- 
cordingly, the choice of fibrous or good friable land which has a constant, 
abundant soil ventilation will be the best precaution against the disease. 

The Rootblight of Sugar and Fodder Beets. 

As rootblight we designate a disease of the tissues which can set in 
even when the young seedlings unfold their cotyledons or begin to open the 
first leaflets. A black spot appears on the stem below the seed leaves which 
spreads further toward the root end (less toward the cotyledons) and be- 
comes depressed. Even if the young seedling has not reached the upper 
surace of the soil, the first stages of the disease can be recognized. Vanha 
observed that the tissue becomes glassy before turning brown. The little 
plants begin to wilt and usually break at the diseased point. Death results 
at once. If the disease is limited to a small area on the hypocotyledon stem 
and the plant does not succumb, the depressed place will heal and a normal, 
later growth follows. Because the diseased place blackens and often 
shrinks to the size of a thread below the seed leaves the practical grower 
also calls the appearance "black leg" or the "threads." The same term is 
used as well in the blackening and softening of the hypocotyledons of cab- 
bage plants, which arise, however, from other conditions. 



221 

It is noteworthy that often great numbers of beet seedlings are diseased, 
and yet frequently perfectly healthy plants may be formed close to the dis- 
eased ones. It should be emphasized further that, when the disease develops at 
all it is found simultaneously in all parts of the field, and that, as a rule, iso- 
lated spots are not attacked in the middle of diseased fields. As the plants be- 
come older, the rootblight ceases. The healed plants usually, however, remain 
below the healthy ones in size and sugar content and show a tendency to- 
ward root splitting and other deformities. Stoklasa^ emphasizes the fact 
that all varieties are not equally susceptible to rootblight. 

The disease has been known since the increase in beet culture in the 
30's of the last century and, according to Stift^, the discussion as to the 
cause of the phenomenon began in 1858 at the meeting of the beet sugar 
manufacturers of the Zollverein. At that time the opinion was expressed 
by practical growers that the trouble was due to the physical condition of 
the soil, i. e., a too great solidity of the soil. It was emphasized that root- 
blight was found only where the upper surface of the soil was hard and had 
not been loosened on which account a thorough cultivation and stirring were 
advisable. 

At the time scientists took up the question, the parasitic theory was 
already at the crest of its development. At first Julius Kiihn in 1859 gave 
expression to the opinion that the moss button beetle (Atomaria linearis 
Stephn.) attacked the plants, and, where it had eaten, the rootblight made its 
appearance. I have observed something similar^. The centipede and such 
animals were also cited as causes. This theory which prevailed for many 
years was first upset when Hellriegel found that the disease could be pro- 
duced without animal injury and in many cases came from the beet- 
seed. As a result he advised a soaking of the beet-seed for 20 hours in a 
one per cent, carbolic acid solution*. Karlson, at about the same time, 
ascribed the phenomenon to a special fungus and in this emphasized the fact 
that only weak specimens succumbed to rootblight. Seedlings from very 
good seed or those which were strengthened by an energetic growth, would 
not be overcome by the fungus carried in these seed balls (Scleranthus)^. 
The experiments in sterilizing with carbolic acid and with copper sulfate 
showed a decrease of the rootblight. In spite of the advantage due to ster- 
ilization, Karlson lays especial stress on the selection of especially strong 
seedlings and lays the responsibility for the spread of rootblight on our 
present cultural methods'', which aim only at obtaining large amounts of 
seed and neglect the quality. 

1 Stoklasa, Jul., Wurzelbrand der Ziickerriibe. Central bl. f. Bakteriologie. Sec- 
tion II, 1898, p. 687. 

2 Stift, Anton, Die Krankheiten der Zucl?:errube. Wien 1900. Verlag des Cen- 
tralver. f. Riibenzuckerindustrie. 

3 Zeitschr. f. Pflanzenkr., 1892, p. 278. 

4 Hellriegel, Ueber die Schadigung junger Riiben durch Wurzelbrand etc. 
Deutsche Zuckcrindustrie, Jahrg. XV, p. 745. Biedermann's Centralbl. 1S90. p. 647. 

5 HoUrung also found a lesser degree of disease in sowing large beet seed balls 
(Scleranthus). Dritt. Jahresb. d. Versuclis.stat. f. Nematodenvertilgung. 1892. 

6 Blatter fiir Zuckerriibenbau, 1900, No. 17. 



The theory of seed steriUzation was further developed by Wimmer, one 
of Hellriegel's collaborators. Of the different substances used in sterilizing, 
carbolic acid was proved to be the most advantageous and, in fact, when 
used in the one per cent, solution of "Aciduni carboHcum crudum lOO per 
cent. Pharm. Germ. II." To one part by weight of seed should be reckoned 
about 6 to 8 parts by weight of liquid. A warm water solution was proved 
favorable as well as a cold water solution^ 

While Wimmer left the question undecided as to the influence of the 
weather and the soil constitution Holdefleiss held to the theory that this 
and not parasitism caused rootblight. In soils favorable to the disease, he 
usually found an abundant amount of ferrous oxid, but comparatively little 
calcium. In this the tendency to choking with mud and incrustation of the 
soil are unmistakable and the discovery that rootblight was cured by abun- 
dant hoeing was in accordance with this. On this account Holdefleiss 
recommends, in addition to a continued, open condition of beet soils, a rich 
addition of burned (quick) lime (12 to 15 centner German per acre)- which 
is given with the best results to the first grown crops and not directly to the 
beet. Loges^ had good results from the addition of 7 cent, of quick-lime per 
acre. As a further contributory factor, Hollrung emphasizes a lower temper- 
ature and the fact that rootblight never extends above the surface of the soil 
to the aerial parts of the axis which are exposed to air currents. He asserts 
definitely that rootblight is brought about by physical and chemical causes 
making themselves felt in cold soil, impermeable to air currents. The theory 
that the soils, in which black leg of the beet occurs, are easily choked with 
mud and become hard is substantiated by Marek and Krawczynski. Ac- 
cording to Stift's statement (loc. cit. 10 to 20) in such a soil 77.25 per cent, 
fine sand was found. 

Opposed to these theories, shared by many other investigators, the par- 
asitic theory was still maintained and found its most active defender in 
Frank. Frank, with Kriiger, from 1892 on, made various experiments and 
determined that, besides the Pythium de Baryanum found by Lohde, and oc- 
curring in many diseases of seedling plants from very different genera, be- 
sides the Rhisoctonia violacea mentioned by Eidam, there was a specific 
beet fungus, Phoma Betae Frank, "which not only causes heart and dry rot 
of the mature beet, but also the rootblight of the young beet roots."'* Re- 
peated discoveries in field experiments, however, soon showed even this 
investigator that weather and soil conditions exert a decisive influence. "It 
is still undecided whether the seedling thereby becomes more susceptible to 
the fungus attack or whether this is not sufficiently explained by the fact 
that cold weather delays the growth and the plant remains unusually long 



1 Hollrung, in Zeitschr. f. Riibenzuckerindustrie i. D. R. Vol. 46. Part 482. 

2 1 Centner in German weights equals 50 kg-, or approximately 112 English 
pounds. 

3 Bericht. d. Landw. Versuchsstation Posen. 1891. 

4 Frank, A. B. Kampfbuch gegen die Schadlinge unserer Feldfriichte. Berlin, 
Paul Parey, 1897, p. 117. 



223 

in an immature condition which is especially susceptible to the disease, while 
seedlings forced by heat pass rapidly through the susceptible stage and thus 
escape the danger." 

In this explanation, after many modifications of Frank's original state- 
ment, is expressed the theory that besides this specific excitor of disease, 
Phoma, a definite degree of susceptibility of the beet seedling must exist for 
the production of rootblight. Sorauer held this point of view earlier since 
he proved that rootblight can exist without the presence of Phoma and that, 
instead of this, bacterial growth accompanies the disease. We owe the most 
thorough investigations of the bacteria of rootblight to Hiltner, whose recent 
studies we will consider with great thoroughness after sketching Stoklasa's 
theory. According to Stiff's statements (loc. cit. p. 17) Stoklasa admits that 
bacteria can produce rootblight in beets, and he considers the following 
species capable of doing so: — Bacillus subtilis, B. liquefaciens, B. fluore- 
scens liquefaciens, B. mesentericus vulgatus and B. mycoides; Linhardt de- 
clares the latter to be the essential cause of injury. Recently Pseudomonas 
campestris has been added to these. Stoklasa considers that the above men- 
tioned atmospheric and soil conditions produce a predisposition in the beet 
seedlings. He turned his attention especially to oxalic acid, normally formed 
by the life process of the plant as potassium oxalate. Soluble oxalates, 
which act as poisons, are transformed into an insoluble calcium oxalate, if 
calcium oxide can be taken from the soil by the root hairs. By thus neut- 
ralizing the oxalic acid its retarding action on the process of assimilation 
ceases and the plant recovers. If much nitric acid is present in the soil or is 
added in excess (strong fertilisation with nitrate of soda), an hastened de- 
velopment takes place at any rate, but at the same time the oxalic acid con- 
tent increases. In such a case, if the young beet plant cannot take up suf- 
ficient calcium, it becomes predisposed to rootblight. 

As already said, we owe the most thorough study of the relation of bac- 
teria to this disease to Hiltner and Peters^ These investigators made a 
number of experiments and found that there are soils which almost never 
show any rootblight and, conversely, there are others in which the disease al- 
most always appears. They concluded from this, that many soils are in a con- 
dition to lend a certain protective power and they perceive that this pro- 
tective peculiarity is the ability of the immunizing soil to provide the outer- 
most cell layers of the roots of the beet seedling with such micro-organisms 
as can prevent the penetration of fungi and bacteria producing rootblight. 
Hiltner and Peters call this protective sheath, which they had observed 
similarly in peas, "Bacteriorhiza." If its formation be prevented by steri- 
lizing the soil and killing the protective soil organisms, in case the seed had 
not been previously sterilized, the fungi and bacteria causing rootblight 
could enter the young seedlings and destroy them. 



1 Hiltner, L,., and Peters, L., Untersuchungen liber die Keimling-sl^ranlcheiten 
der Zuelzer- und Runkelriiben. Arb. d. Biolog. Abt. f. Land-und Forstwirtsch. am 
Kais. G-esundheitsamt, Vol. IV, Part 3, 1D04, p. 207. 



224 

The words of Hiltner and Peters themselves best show how little the 
organisms per se are to be feared and how the chief cause of the disease is to 
be sought in the conditions making the plants susceptible. In speaking of 
the results of their experiments, they say (loc. cit. p. 249) "this result, how- 
ever, shows that the production of diseased seedlings in the seed bed presents 
a rather complicated phenomenon. This cannot be laid exclusively to the face 
(heretofore almost universally accepted) that parasitic fungi or bacteria ac- 
cumulate on the seed balls, then passing over to the roots, for these organ- 
isms in themselves cannot cause the diseased conditions of the beet. Only 
after the resistance of the roots has been weakened by the influence of cer- 
tain substances, viz., oxalates, can otherwise harmless parasites attack them." 

According to Hiltner's theory, the substances or circumstances predis- 
posing a plant to disease are produced by the decomposition of the tissue in 
the seed balls, either on the field as a result of unfavorable weather, or later 
in storage because of too great warmth. 

A work by Sigmund^ reports upon the advance given to the occurrence 
of rootblight by the fact that the micro-organisms especially concerned in 
it (Phoma and Bacillus mycoides) find certain organic compounds in the 
nutrient solution of the host. After he had emphasized the fact that the 
parasites are not able alone to increase the disease, he mentions that the 
number of diseased beet seedlings can be increased if glycocol, uric acid, 
asparagin, hippuric acid, leucin, etc., are found in the nutrient solutions of the 
micro-organisms named and the beet balls are soaked in this nutrient so- 
lution. 



In this important disease we have simply listed, first of all, the various 
theories and results of investigations as they have appeared from time to 
time, in order to show that with all observers, in spite of their very different 
points of view, one statement is found running through all their discussions 
like a red line, viz., the influence of the soil^ This influence shows itself 
most distinctly in heavy,. binding soils. It can make itself felt also on other 
soils if they are encrusted for any reason whatever. The prime factor under 
such conditions is the scarcity of oxygen. At present we cannot say defi- 
nitely what processes are started in the soil, seeds and the young plants. In 
the same way, no definite decision can be made as to whether rootblight is a 
constitutional disease, i. e. a deflection of the normal life functions leading 
to tissue decomposition, or a parasitic process, i. e. a process producing the 
same result but caused by the co-operation of micro-organisms. If, as we 
beUeve, in the majority of cases the latter should be granted, we must bear 
in mind emphatically the fact that these organisms, no matter whether fungi 



1 Sigmund, Wilh. Beitrage zur Kenntnis des Wurzelbrandes der Riibe. Natur- 
wissensch, Zeitschr. f. Land- und Forstwirtschaft, 1905, p. 212. 

2 Further material from practical sources may be found in the annual reports 
of the Special Committee for Plant Protection. (Jahresberichte des Sonderaus- 
schusses fiir Pflanzenschutz. Deutsch. Lnndw.- Gesellsch. 1892-1905). 



225 

or bacteria, can only destroy the seedlings where they have some predis- 
position to take up such organisms. This predisposition is the product of 
the soil in which they are grown under definite atmospheric conditions. 

Therefore, the soil condition is always the first cause affecting the as- 
similatory process and inducing rootblight. The question whether this affec- 
tion always takes place with an excess of free oxalic acid and whether the 
abundance of the acid acting poisonously is due to the formation of more 
acid by the plant body or that less acid is oxidized because of a scarcity of 
oxygen, may be left for later investigation. It is enough for our purpose to 
know that the disease is a result of a binding consistency of the soil under 
unfavorable atmospheric conditions, i. e. cold, wet weather. 

We will now return to the statements of practical workers, who, from 
the beginning, have insisted that the cause of rootblight lies in the condition 
of the soil. 

When citing these expressions, we come to the self-evident regulations 
for fighting it. Briem reports a case from the years 1904-1905^. On a newly 
broken field near Prague in 1904, with cold, wet weather, and a consequent 
slow growth, beets were extensively root blighted although until that time 
the phenomenon had been rare. Also, the beets did not revive completely 
until later. The same field in the following year, after a rich fertilizing with 
potassium, nitrates and phosphates, was again planted with commercial beets. 
As a result of the very wet, cold weather, the seed sprouted only at the end 
of two weeks (on the 24th. of April). It was. feared that, with the weakened 
growth resulting from the cold nights, rootblight would again set in. Fort- 
unately this did not happen and the warm days, coming at the beginning of 
May, soon caused the rapid, vigorous unfolding of the first pair of leaves. 
However, when, on the 20th of May, a violent rain had beaten the field 
down unusually hard so that water could only soak in very slowly, many 
seedlings showed the beginning of rootblight after five days. This example 
of the result of a sudden exclusion of the air from soil, beaten hard by rain, 
shows therefore that it is primarily advisable to'> keep the upper surface of 
the soil constantly open by cultivation. Secondarily, even if the soil contains 
lime, a further supply of quick lime must be given. The effect of the lime 
must not always be considered as a nutritive means, but as a mechanical one 
for improving the soil since it increases its friability. Superphosphate has 
given good results-. In fields liable to these conditions, increased attention 
should be given to the use of as vigorous seed as possible. 

If one wishes to sterihze the seed which, according to our theory, is of 
very little advantage^, a carbolic acid solution should be used. For the 
sterilization of one hundred and twelve pounds of beet seeds 1.5 k. carbolic 



1 Briem, H., Wurzelbrandentdeckung und kein Ende. Blatter f. Zuckerriibenbau 
V. June 15, 1905. 

2 Zeitschr. f. Pflanzenkrankh., 1896. p. 54 and p. 340. Landwirt, 1896, Nos. 15, 17, 
21. Jahresber. d. Sonderausschusses f. Pflanzenschutz, 1902. 

3 Hiltner in Mitteil. d. pflanzenphysiolog-. Versuchsstat. Tharand. Sachs, landw. 
Zeit. 1904, Nos. 16-18. 



226 

acid (Acidum carbolicum liquidum crudum loo %) or the more expensive, 
pure crystallized acid in 3 hi. water. To test the acid's desired solubiUty, 0.5 
grams should be shaken thoroughly in one litre of water; this should dis- 
solve in from 5 to 10 minutes. When the sterilizing solution is ready, 
the seeds are poured into it and stirred about repeatedly and vigor- 
ously in the course of the next few hours. Then the seed is pressed down 
with weighted boards so that it remains entirely covered by the solution. 
After about 20 hours it is taken out and spread in a thin layer in an airy 
place and stirred often with a rake. As soon as it is sufficiently dry it can 
be planted with a drill, but it may lie for some time, when completely dry, 
without being injured. 

If it is desirable to use the sterilizing solution several times, it is neces- 
sary only to replace the liquid lost by pouring in the needed quantity of a 
stock solution. However, considering the cheapness of the material, it is 
well not to use the solution too often^. 

Instead of sterilization, the coating of the seed with calcium carbonate 
seems to us to be advantageous. 

But the main thing is to work the soil, for even the most carefully 
handled seed, found to be faultless in the germinating tests, can become dis- 
eased. Hiltner, in his above-mentioned work, gives some suggestions in this 
connection which are well worth consideration. Up to the present in trade, 
the quality of the seed has been tested according to its behavior in the seed 
bed, by means of a suitable method. It is now seen, that the number of 
diseased seedlings increases, the longer the seed is left in the seed bed. Ex- 
periments show tliat if, for example, the seedlings are taken from the sand 
seed bed on the 9th day, often more than ten times as many are found to be 
diseased as when taken out on the 6th day. To this it should be added that 
if the seeds lie close to each other the mutual infection is considerable. Be- 
sides this, the number of diseased seedUngs differs greatly, depending upon 
whether the seed was soaked or not and whether distilled water, water 
free from calcium, or water containing calcium, was used for the soaking. 
If finally it is taken into consideration that the constitution of the soil de- 
cides the subsequent behavior of the seedlings, it will be concluded that the 
methods at present used for judging of the quality of the seed give no pro- 
tection and no standard for beet seed. In order to obtain an insight into the 
germinating power, the best seeds will have to be tested in as many germi- 
nating seed beds as possible and with different methods-. The best germinat- 
ing results, however, in no way give a guarantee as to rootblight. This depends 
upon whether the micro-organisms present in the dried blossoms, containing 
the seeds, find an opportunity of so developing in the soil that they can attack 
the young seedlings. 

1 Wilfarth, H., and Wimmer, G., Die Bekampfung' des Wurzelbrandes der Riiben 
durch Samenbeizung. Zeitschr. d. Vereins d. Deutschen Zuckerindustrie, Vol. 50, 
Part 529. 

2 For the difference in germination of the seed treated in the same way but 
sown in sand and in soil, compare the reports by Marek in tlie year Book of the 
German Agricultural Society. (Jahrb. d. Deutsch. Landwirtsch. Ges. 1892.) 



^27 

Tropical Plants. 

In consideration of my standpoint, that in much of our cuhivation too 
little account is taken of the soil conditions, especially of its physical consti- 
tution, I think it necessary to refer also to the demands of tropical plants on 
the physical peculiarities of the cultivated land. In regard to tropical plants, 
I base my theory on the statements of Fesca^ who has often given his own 
experiences, and further, on the recent publications of the Biological Agri- 
cultural Institute at Amani-. 

As we shall see, in these injuries, as in those in temperate cHmates, 
phenomena are often involved which are due to scarcit)^ of oxygen mani- 
fested in heavy soil or in soils which have become compacted through culti- 
vation. Many plants in the tropics can develop accessory organs with a scar- 
city of oxygen, like the adventitious roots from the trunks of trees buried or 
covered with slime. The palms (Phoenix, Kentia, Chamaerops etc.) can 
develop root branches growing perpendicularly out of the soil which have a 
peculiar respiratory arrangement (Pneumathodes) ; this appears as a mealy 
coating extending backward for a certain distance from the tip of the root. 
This mealy condition is produced by the increase, enlargement and breaking 
up of the outer layers of the rootbark with a rupturing of the epidermis and 
an almost complete suppression of the schlerenchymatic ring. Jost^ deter- 
mined experimentally with Phoenix that these pneumathodes remain in the 
soil when it is well aerated, but, on the other hand, are raised above the sur- 
face of the pot if it is submerged in water. Similar arrangements were 
found also in Pandanus, Saccharum and Cyperus. 

Root-Rot of the Sugar Cane. 

Among the numerous diseases of sugar cane, root-rot plays a prominent 
part. In Java it is considered the worst enemy of sugar cane culture. Nat- 
urally growers have not failed to cite the micro-organisms (Vertlcillium. 
(Hypocrea) Sacchari, Cladosporium javanicum Wakker. Allentospora rad- 
icle ola, Wakker, Pythium etc.) colonizing on the diseased roots as its cause. 
Nevertheless Kamerling's'' recent experiments have now confirmed beyond 
all doubt the supposition that a constitutional disease is concerned here, 



1 Fesca, Der Pflanzenbau in den Tropen und Subtropen. Berlin Siisserott. Vol. 
I, 1904. 

2 As said above, the statements on the phenomena of disease in cultivated 
tropcal plants serve chiefly as proof of the necessary consideration of soil and at- 
mospheric conditions as a cause of disease. In the descriptions we can sum up the 
material more briefly since abundant literature easily makes possible special 
studies. Besides the magazines already mentioned, pp. 65 to 67, the recent publica- 
tions of the Usambara-Post furnish valuable material. "Der Pflanzer," Adviser for 
Tropial Agriculture" issued with the co-operation of the Biological Agricultural In- 
stitute, Amani, by the Usambara-Post, 1905. ("Der Pflanzer," Ratgeber fiir tropische 
Landwirtschaft unter Mitwirkung des Biologisch-Landwirtschaftlichen Institutes 
Amani, herausgageben durch die Usambara-Post, 1905.) 

3 Jost, Ein Beitrag, zur Kenntnis der Atmungsorgane der Pflanzen. Bot. Zeit 
1887, No. 37. 

* Kamerling, Z., Verslag van het Wortelrot-Oenderzoek, Soerabaia, 1903, 209 
pages, with 19 Plates. 



228 

resulting from compacting the soil. Raciborski with Suringar^ has expressed 
the theory, earlier proved, that by transplanting sugar cane, which had suf- 
fered from this root disease, known as Dongkellanziekte , to other soil, the 
plants would become healthy. The disease occurs especially on heavy clay 
soils and manifests itself in Java, when at the beginning of the spring mon- 
soon the plants die with alarming rapidity after they have already shown for 
some time an abnormal branching of roots and also deformed root hairs. He 
investigated the soils in which the disease occurred and found that they did 
not have sufficient friability and easily became compacted. The permeabil- 
ity of the soil can be increased by supplying humus, since this, as also ferric 
hydroxide, or silicate rich in iron, favors the formation of friable soils. Since 
the humus is gradually lost by oxidation, care must also be taken to retain the 
porosity of the soil by a renewed supply of stable manure, rice straw or 
green fertilizer (compost). 

According to Wakker's- studies, many leaf spot diseases seem either 
directly produced by moisture in the soil (if of a parasitic nature) or favored 
by this moisture. Wakker found in the vicinity of Malang "a yellow streak- 
ed, banded disease," "rust," "ring spot disease," as well as the red and yellow- 
spot disease. While he considers the first named as a parasitic phenomenon 
favored by moisture, he explains the yellow spot disease, in which the leaves 
acquire somewhat elongated, greenish yellow spots running into one another, 
as a hereditary constitutional disease. 

Diseases of Cotton. 

The majority of the cotton diseases may be considered at present to be 
of parasitic origin, but I doubt if this will always remain the case. With the 
conviction that many of the micro-organisms already found are to be con- 
sidered parasites of weakness, naturally the first existing factor must be 
considered as decisive, viz., the disturbance in nutrition causing the weak- 
ness which first offers the possibility of infection by the fungus. This will 
have to be sought primarily in weather and soil conditions. 

Examples of disease, in which only the soil is considered as the cause 
in the rainy season, are reported by Vosseler^ from our East African col- 
onies. In 1904, in the district of Kelwa, there occurred a "browning of the 
stems," which produced greater damage in that region than all the other 
diseases which had appeared up to that time. Brownish black spots were 
produced in the bark below the tip of the main shoot, as a result of which 
followed the dying of this part as well as of the upper lateral shoots. The 
disease appeared, however, only on so-called sour soil. 



1 Kamerling, Z., en Suringar, H., Oenderzoeking-en over onvoidoenden groei en 
ontijdig Afsterven van het riet als gevolg van wortelziekten. Mededeelingen van 
het Proefstation vor Suikerriet en West- Java, No. 48; cit. Zeitschr. f. Pflanzenkr., 
1901, p. 274, and 1904, p. 88. 

2 Wakker, J. H., De Bladzeikten te Malang. Archiev voor de Java-Suikerindus- 
trie, 1894. Aflevering 1. 

3 Vossler, Zvs^ei Baunnvollkrankheiten. Immune Baumwollsorten. Mitteil. 
Biolog.-Landwirtsch. Institut Amani, 1904, No. 32. 



:229 

The red spot disease of the leaves, occurring to a devastating extent 
along the whole coast, was a second phenomenon. A pale border appeared 
along the edge of the leaves ; the zone was distinctly cut off from the inner 
portions by a zigzag line. Dark red spots, or a uniform red coloration with 
which a deforming of the leaf surface was often connected, then appeared. 
The disappearance of this trouble with the appearance of drought indicates 
that the soil during the prevailing wet weather had unfavorably affected the 
growth of the cotton. Vosseler seems to suspect that the dreaded "wilt dis- 
ease" should be included among the chmatic diseases and refers in this to 
the possibility of producing immune races by growing plants from seed of 
healthy stock in diseased fields. According to Schellmann^, cotton cannot 
grow on stiff clay soils and sour humus soils. 

Castor Bean Cultures. 

Although Ricinus thrives in subtropical and even in temperate zones, 
according to Zimmermann-, it is extensively cultivated only in the tropics 
where it grows from sea level up to possibly 1600 m. The oily seeds are the 
desired crop. At any rate an abundant supply of nutriment is needed for 
Ricinus, since it makes very great demands on the soil. The plant also re- 
quires large amounts of water while growing. Later, however, the physical 
constitution of the soil has a determining value in the matter, since the plants 
do not thrive in all soils which, not well drained, remain constantly 
wet. These observations in the tropics correspond with our experience in 
growing Ricinus as a decorative plant. Only the plants develop well which 
have plenty of room and a porous soil, rich in nutriment. When grown in 
pots, to which much nutriment is added by fertilizing salts, the earth becomes 
encrusted and the plants remain small and weak. 

Tobacco. 

Very instructive examples of the determinative influence of the soil are 
furnished by Hunger's^ observations on the development of the Delhi- 
tobacco and its different behavior toward the "Mosaic Disease," which will 
be reported more fully in the section on enzymatic diseases. 

Hunger says that a soil of white clay in which much sand has been 
mixed, is the best for thin-leaved tobacco if the amount of precipitation is 
favorable, but at the same time this also favors most the abundant appear- 
ance of the mosaic disease in the form of the so-called "gay-head." Here, 
after topping, the plant gives the impression of having made too rapid 
growth; long internodes, a yellowish-green foliage, a great many lateral 
shoots, all of which are sickly. 



1 Der Pflanzer, Usambara-Post, 1905, No. 1. Here also older literature. 

2 Zimmerman, A., Die Ricinus-Kultur. Der Pflanzer, Ratgeber fiir tropische 
Landwirtscliaft unter Mitwirkung- des Biolog-isch-Landwirtsch. Institutes Amani, 
herausg. durch d. Usambara-Post 

3 Zeitschr. f. Pflanzenkrankh. 1905, Part 5. Hunger, as Botanist at the experi- 
mental station for Dellii- Tobacco (VIII Abt. d. Bot. Gart. zu Buitenzorg) has had at 
his disposal most extensive material for observation. 



2T,0 

If the clay soil lacks sand, however, and becomes loamy, it is useless 
for tobacco culture. The roots of the plant develop scantily and are often 
deformed. The leaves are not of the right length and are of poor quality. 
The mosaic disease appears a week or two after transplanting. The red, 
atmospherically disintegrated soils of Ober-Langkat are pretty compact and 
here the plants are squatty ; the leaves standing close above one another are 
not especially thin while the mosaic disease occurs rarely. It only appears 
exceptionally on the shoots which, after topping, develop sparsely. 

On dark soils rich in humus, tobacco has an enormous, well-proportioned 
development ; the very large leaves are dark green and thin. The mosaic 
disease abounds. 

This disease scarcely, if ever, occurs on the peaty, porous, Paja soil, 
which has a high water-holding capacity. The enormous leaves almost 
never wilt in the soil containing much water, but are very thick and rich in 
oil; with fermentation they become dark colored and are therefore not very 
valuable. On fresh Paja soil the mosaic disease cannot be produced even 
by topping. 

Coffee. 

The tree, which of all our tropical plants deserves the most consider- 
ation, coffee, is extremely susceptible to soil conditions ; although droughts 
are not favorable and it likes best to grow in soil which even at a time of 
drought keeps fresh, yet it withstands drought much better than too much 
moisture. If, during the rainy season, it is covered with water for only a 
few days, it becomes irretrievably diseased. A sufficient capacity for water 
in the soil, combined with abundant aeration, is therefore its chief need. 
Freshly cleared forest soil is found to be especially favorable for its culti- 
vation. Black rust (swarte roest) and canker diseases (Natalkrebs and Java- 
krebs) (Djamoer oepas) with their diseased cambium are probably physiolo- 
gical disturbances introduced by unfavorable soil and atmospheric conditions 
and result later in fungus attack. The Liberian coffee is said to be less sus- 
ceptible to impervious soil than the Arabian, and flourishes where the latter 
fails^ 

The leaf disease described by Zimmermann as "Blorokziekte"- seems 
to me also to belong here. The leaves develop convex, yellow spots. Later, 
the epidermis ruptures on these spots and the cell contents turn brown. The 
trees in Java, to be sure, are not killed by this disease, but their fertility is 
greatly reduced. As the result of an excessive water supply, Zimmermann 
observed^ the so-called "little stars," occurring rarely in Coffea liberica and 
more frequently in C arahica; i.e. blossoms which open prematurely when 
incompletely developed and therefore remain sterile. The disease should 



1 Delacroix, G., Les maladies et les ennemis des cafeiers. II 6dit. Paris, Chala- 
mel, 1900, p. 8. 

2 Teysmannia 1901, p. 419. 

3 Eenige Pathologische en Physiologische Waarneminger over Koffle. Mededee- 
lingen uit S'Lands Plantentuin, LXVII. 



23t 

not be confused with the black discoloration of the blossom buds passing 
under the same name. These buds finally fall off unopened. Different kinds 
of root moulds have been described and considered as the cause of root-rof^. 
I think it will be necessary to study here the question whether parasitic 
fungous forms can attack the plant injuriously only when the roots have 
already been weakened by unfavorable nutritive conditions. 

Cocoa and Tea. 

Fesca says in regard to the cocoa tree "extremes of soil structure, poor 
sand, as well as tough clay, are not favorable to the cocoa tree. Rather it 
demands greater soil depth and freshness, without the necessity of enduring 
standing water, as well as greater humus and nutrition content, than does 
coffee." The same author, who himself has analyzed good tea soils in Japan, 
say of tea, that he found in a more compact soil, 30 to 40 per cent, of water 
as capillary water. Tea demands a sufficiently deep soil which is free from 
standing water, to which it is very sensitive. Here too a still little understood 
fungus is described as the cause of a root disease. It is said to result in the 
early death of the bushes, especially when growing on damp soil. Neverthe- 
less Fesca" assures us that he has never yet seen the disease on well aerated 
soils. We might also trace the diseases of young tea plants described by 
Zimmermann^ to an unfavorable place of growth, although a fungus bearing 
lobed haustoria has been observed at the disease centres. The leaves become 
flabby and discolored ; the stems turn brown at the base or higher up where 
the root seems healthy. Often only the leaves show brown spots, especially 
on the midrib. The fungi developed from the diseased parts of the stem 
(Nectrieae) could not produce the disease even in infection experiments. 
In dry weather the disease decreases considerably. Also transplanting the 
seedlings from the closely planted seed bed arrested the disease. If we have 
considered here with the greatest brevity the soil demands of our most impor- 
tant cultivated tropical plants, it must still be added that naturally the climate 
remains the decisive factor. Among these climatic factors especial attention 
must be given to humidity since the quality of the harvest often depends 
considerably upon this. In cocoa plantations in Kamerun, for instance, it 
may be observed that the quantitative production of the trees is unusually 
abundant, but the quality of the fruit is only mediocre as the result of great 
dampness. The trees also are short-lived here. 

Other Tropical Plants. 

Of grains. Maize requires, first of all, a deep, mellow soil free from 
standing water and cannot thrive on tough clay. Sorghum behaves similarly, 
but is still more sensitive to cold and dampness and, because of its deep root 



1 Bolletirii del Institto Fisico-Geographico de Costa Rica, 1901. 

2 Loc. cit., p. 273. 

3 Zimmermann, Untersuchungren iiber tropische Pflanzenkrankheiten. Sonder- 
berichte iiber Lan- und Porstwirtschaft in Deutsch-Ostafrika, Vol. II, Part 1, 1904. 



232 

system, is very resistant to drought. This accounts for its growth on tropi- 
cal and subtropical steppes. The Negro or brush millet (Pennisetum spica- 
tum) is entirely unsuitable for firm soil, but is excellent for porous soils in 
dry localities. The other millet varieties behave similarly. 

The Leguminoseae, which are suitable for growth as a second crop be- 
cause of their usually short vegetative period, may, in the tropics and sub- 
tropics, acquire great importance not only as collectors of nitrogen and as an 
excellent nutritive substance, but are also valuable on account of their close 
shading of the soil, preventing it from hardening and'as soil loosening, green 
manuring plants. The plants make good growth in dry soils ; — accordingly 
. heavy soils, in regions with abundant precipitation, are not suitable for them. 
Busse^ has given more detailed studies of sorghum diseases and their rela- 
tions to atmospheric conditions. 

Of tuberous plants, the sweet potato requires about the same cultural 
conditions as our potato. The cassavas (Manniok) require deep, loose, dry 
soils, but rich in humus. The moisture-loving Maranta species, furnishing 
arrowroot, also requires looseness of the soil, on which account virgin soil is 
found to be less suitable because of its compactness. P2ven Taro, the tubers 
of the different Colocasia species, which requires a great deal of moisture, 
flourishes only when the soil is pervious. The same is true of the Yam, 
which is derived from different species of the genus Dioscora. In regard to 
poppy culture and the harvesting of opium, reference should be made to 
Braun's^ work, and in regard to rubber plants and especially the Liana, 
root and herbaceous rubber plants, to studies by Zimmermann^. 

Means for Overcoming the Disadvantages of Heavy Soils. 

Drainage. In this we have to take into consideration not only soils 
rich in clay, but also those sandy ones whose graular structure is so fine 
that they can become as closely compacted as clay soils. 

Of the practical means used to increase soil aeration, drainage deserves 
to be named primarily. It facilitates the exchange of air in the soil inter- 
stices as well as removing stagnant water accumulations after every rain. 
The drainage pipe acts as an apparatus for sucking up air. When the rain 
fills the soil, it forces out the air which has a less oxygen content than the 
atmosphere, but is richer in carbon dioxid. But since the rain is quickly 
soaked through the drains, air rich in oxygen streams just as quickly from 
the surface down into the pores increasing, thereby, the processes of oxida- 
tion in the soil and the activity of the roots and micro-organisms needing 
oxygen. 

The fear that drainage will impoverish the fields has rarely any founda- 
tion, since the numerous analyses of drain water show only slight traces of 



1 Busse, Walter, Untersuchungen iiber die Krankheiten der Sorghum-Hirse. Arb. 
d. Biolog-. Abt. f. Land- u. Forstwirtschaft a. Kais. Gesundheitsamte, Vol. IV, Part 4. 
1904. 

2 Der Pflanzer, 1905, No. 11-12. 

3 Ibid, Nos, 8-10. 



233 

potassium and ammonia as well as phosphoric acid, which had been ab- 
sorbed by the friable soil. Nitrates, because of their easy solubility, at any 
rate, are lost in larger amounts, but they are also partially washed away 
from undrained soil into the subsoil. 

Further, the soil capacity for heat, increasing with drainage, should not 
be underestimated as well as the improvement of the crop produced, of 
which it may be said in general that damp, and therefore cold, soil produces 
crops poorer in nutriment. The reason why damp soil is cold is evidenL 
from considering the fact that if water has a specific heat equal to one, the 
highest specific warmth ever shown by soil is only equal to 0.5 ; i. e. at most 
lialf that of water. If this water which is the hardest to warm is removed 
by drainage, the soil must become warmer. Previous to drainage, the soil 
remained cold until late in the spring, thus causing a later awakening of 
vegetation and a later germination of the seed. A cold place of growth is 
especially disturbing to young plants, since it holds development back in a 
developing phase, which is determinative for the whole later plant. The 
root system becomes poor, the appearance sick, and later favorable temper- 
ature conditions are not able to overcome the bad condition. One of Stock- 
hardt's^ experiments with winter r^'e may serve as an example. The ex- 
perimental plots differed in drainage and soil porosity. One plot was 
traversed at a slight depth by a drain possibly 2.5 cm. wide and in such a 
way that the pipe, bent at right angles at one end of the drain, opened like 
a chimney toward the upper surface of the soil. The soil of this plot, as 
well as that of the undrained one, was broken up 50 cm. deep, while a third 
plot was dug only 25 cm. deep and not drained. In corroboration of earlier 
results obtained with lupin, oats and the like, the harvest showed an ap- 
preciable excess on the drained lot, although the young plants showed no 
difference before spring. 

Reckoned per acre this crop amounted as follows : 

Grain Straw Totals 

and Chaff 
kg. kg. kg. 

Part I, drained and dug 50 cm. deep 539 1470 2009 

Part II, undrained and dug 50 cm. deep 411 928.5 1339-5 

Part III, undrained and dug 25 cm. deep 338 859.5 1 197-5 

Grain content Nitrogen content 

per bu. of the grain 

Lot I. 40.80 kg. 2.18 per cent. 

Lot II. 39-85 kg. 1.83 " " 

Lot III. 37-70 kg. 1.83 " " 

Patz-, referring to the use of drainage for removing iron from newly 
broken soil, says, "usually iron is found directly under the surface of the 
soil and at the height of the usual ground water level. The ground water 



1 Chemische Ackersmann, 1859, p. 232; 1861, p. 100; 1864, p. 22. 

2 Hannoversche landw. Zeit. 1880, No. 45; cit. Biederm. Centralbl. f. Agrik.- 
Chemie, 1880, p. 911. 



234 

carries the iron upward and in many cases cements the sand grains in the 
soil at the usual height of the ground water level in such a way that often in 
laying a drain, a hard, stone-like, red soil is found. By laying drains cor- 
rectly and systematically, with the horizontal drains intersected at right 
angles by the absorbing drains, the latter having at least a depth of 1.2 m. 
and the distance between every two drains being kept 10 times the depth, 
the level of the ground water will be lowered to the depth of the drain and 
no more iron will be carried to the soil above the pipes. The iron already 
present in the soil will be dissolved by the atmospheric precipitation and led 
to the dainage pipes or it will remain in the soil as the non-injurious oxid." 

Working of the soil. Where there is no need of carrying away 
excessive water, furrowing and deep plowing, instead of drainage, will often 
serve the same end. In this care must be exercised if, with fertile, friable 
soil, there is a prospect of bringing a dead subsoil to the upper surface by 
the furrowing or plowing. In addition to fertilizing each time, the gradual 
deepening of the friable soil should take place at least over a period of 
several years. Since, with the deepening of the friable soil, the root surface 
becomes extended and, accordingly, an increased harvest. takes place with a 
greater utilization of the soil, an increased supply of manure is demanded 
with the increasing loosening of the soil. 

In soils inclined to crust, but otherwise not unfavorably constituted 
physically, hoeing and hilling suffice for increasing the soil aeration. This 
cultivation, which can scarcely be sufficiently recommended to the agricul- 
turist and the gardener, and which can be used in any soil, regulates the soil 
moisture. 

Some good, practical experiences as to the advantages of loosening the 
soil, may be found in the reports of the German Agricultural Society's 
special committee for the protection of plants (Landwirtschaft-Gesell- 
schaft). We will cite a single example which is supported by comparative 
experimental cultures. In Skollmen^ (East Prussia) Mentzel divided into 
two parts a field planted with mixed Swedish wheat, Epp wheat and Kas- 
tromer wheat, and kept one half of it loose by harrowing after every rain, — ^ 
i. e. by working with the narrow bladed cultivator, — but did not work the 
other half. Although its soil was better, the latter half yielded only 2160 
kg. per acre, the former, however, 2650 kg. 

A green manure fertihzer turned over deep in light soils and super- 
ficially in heavy soils, acts in the same way as this loosening of the soil sur- 
face. By means of this green manure the capillary raising of the water 
from the underlyng soil layers especially is interrupted". On the one hand, 
the moisture is thus retained in the deeper layers of the lighter soil; on the 
other hand, in heavy, wet soils, a well aerated, friable surface is formed so 



1 Jahresb. d. Sond.-Aussch. f. Pflanzenschutz. Arb. d. Deutsch. Landwirtsch.- 
Ges., Part 107, 1905, p. 64. 

2 King, F. H., Tenth Annual Report of the Agric. Exper. Stat, of Wisconsin, 1884. 
p. 194. 



235 

that the seeds can germinate normally. The stronger, more sturdy plants, 
which have passed through the most critical germinative stages, are then 
better able to combat the soil moisture, which rises capillarily higher and 
more rapidly after the green manure has decomposed. 

Freezing. The loosening of heavy soils in winter through a suitable 
freezing is of the greatest importance in their cultivation. If we take into 
consideration that water, when converted into ice, expands about one- 
eleventh of its volume, it is evident that the more closely lying soil particles 
are forced apart by the ice crystals. Also, since rocks are covered with a 
network of fine cracks, into which the water gradually soaks, the frost is 
constantly decomposing them and in fact the effects are greater as the 
freezing and thawing alternate during the winter. Naturally the rapidity of 
the action will depend upon the composition of the soil, i. e. on its water 
content. The smaller this is, the more quickly and deeply the frost can 
penetrate. Therefore, heavy and humus soils will freeze and thaw most 
slowly. WoUny's^ experiments show the advantage accruing to the soil 
from the loosening action of the frost. He had two plots of land loosened 
up in the fall and left lying in open furrozvs, while a third was not worked. 
This plot and one of the two others were turned over in the spring while the 
third was worked only superficially. It was then proved that for the various 
plants cultivated, the yield was smaller from the plot which had not been 
left fallow in the fall, while the largest harvest was given by the one in 
which the open furrows froze during the winter and were broken up once 
more in the spring. 

Mulching. We now come to the advantage derived in heavy soils from 
the covering of the friable surface with litter, after having considered earlier 
the protection given light soils by such a covering. The greatest advantage 
is that the covering substance prevents the compacting of the soil particles 
since it takes up the force of the rain drops and, conducting the water slowly, 
spreads it over the surface of the soil, thereby keeping the friable surface 
more porous. In nurseries the seed also germinates more uniformly in 
covered beds. The weeds do not grow so vigorously and can be more easily 
and completely removed, since they root more superficially in the looser 
soils. 

The great air variations between day and night produce a heavy for- 
mation of dew in the porous covering material. This runs ofl: to the benefit 
of the underlying soil and increases its fertility. If bark is used to a depth 
of I to I ^ inches, it furnishes a covering for the seed beds in winter and, 
in the spring, a protection against the penetration of frost and the cracking of 
the soil. 

Seed and seedling beds should have water given them in June or July. In 
August the ground is harrowed and, in case the bark should then be covered 
too deeply, the exposed soil is covered with new bark. Snares for the control 

1 Wollny, E., Ueber den Einfluss des Winterfrostes auf die Fruchtbarkeit der 
Ackererden. Biedei-mann's Centralbl. 1902, p. 301. 



236 

of the unevitable June bug are made of heaps of scattered, moist bark which 
heats itself. The June bugs lay their eggs in these heaps which later, with 
a part of the underlying earth, are put in a wagon and worked up with peat, 
or lignite, ashes, lime, plaster and organic refuse to a compost pile, which, 
after a year or two, kills the grubs. 

Harrowing. 

Harrowing is a process which should find mention here. Anderegg^ 
has published very noteworthy results of harrowing meadozvs. A meadow 
of uniform soil composition and mould was divided into four equally large 
lots. These yielded, — 

(i). Unharrowed and unfertilized 377 kg. hay 

(2). Unharrowed but fertilized 833 kg. hay 

(3). Harrowed but unfertilized 770 kg. hay 

(4). Harrowed and fertilized 1563 kg. hay 

Harrowing winter sown grains not only re-opens the encrusted soil, but 
also increase considerably the formation of young shoots. Director Con- 
radi^, however, justly points out the fact that the harrow is usuable only if 
the crust is not too thick and the soil not too binding. Also, if an encrusta- 
tion in spring may be foreseen, the seed must be more thickly sown since 
harrowing destroys plants and the sand is thinned. For that reason har- 
rowing is very useful occasionally in thinning the plants. The increased 
standing room for the plants left in place gives a greater supply of light to 
the basal nodes and starts the lateral shoots into a rapid growth and pre- 
vents their too rapid lignification when these buds obtain moisture from the 
earth heaped up by the harrowing. H the earth is not pulverized sufficiently 
by the harrow, the roller, and preferably a wheel roller, must be used in ad- 
dition. In the majority of cases the roller will have to follow the harrow, 
because binding soils are not made absolutely fine by the harrow, and also 
because it is desirable that the earth torn away from the base of the plants 
may be pressed back again. The best time for harrowing depends on the 
development of the plant and the water content of the soil. If the plants 
have grown too far or continuous dry weather prevails, the harrowing 
should be omitted or, in the latter case, should never be carried out without 
a subsquent rolling. 

A few words also might be pertinent here as to the significance of stones 
in the soil. In this connection, Wollny's^ experiments have shown that 
with a high, constant air temperature (during the warmer seasons) soil 
covered with stones and mixed with them is slightly warmer than is that 
free from stones. With a falhng temperature comes the reverse. During 
the daily minimum soil temperature, soil containing stones is for the most 



1 Illustr. landw. Vereinsblatt, 1880; No. 8; cit. in Biederm. Centralbl. f. Agrik.- 
Chemie. 1880, p. 693. 

- From "Der Praktische Landwirt" in Fiihling-'s landw. Zeit., 1880, p. 151. 
3 Wollny, Fuhling's landw. Zeit, 1880, p. 314. 



part colder than that free from stones, while during its maximum it is 
warmer. In regard to conditions of moisture, field soil covered with stones 
is found to be wetter during the warmer seasons than uncovered soil of 
otherwise similar composition. Soil covered with stones lets more water 
slip through than does one not so covered. 

The Use of Lime, Marl and Plaster. 

The importance of lime arises from its chemical action as a direct 
nutritive substance as well as from its properties, which change the mechan- 
ical constitution of the soil. Aside from favoring friability, it should be 
emphasized that the lime attacks the silicate in clay soils and sets free sol- 
uble potassium compounds. By its more rapid destruction of the organic 
substances, it causes a better decomposition of humus. 

In regard to the technique in using lime, it is advisable to keep burnt 
(quick) lime in baskets under water until no more air bubbles arise (possibly 
3 to minutes) and then to heap up the pieces in layers. They decompose 
(slake) of themselves and the lime stone, which lost its carbon dioxid in the 
previous burning, now becomes the white powdery calcium hydroxid 
(Ca(OH)^,) and as such represents slaked lime, which is soluble in 730 
parts of cold water, and only in 1300 parts of boiling water (lime water). 
100 parts of quick lime correspond to 132 parts of slaked lime. The lime 
should be uniformly spread over the field in quiet weather by hand, or with 
a suitable shovel. It is well to spread it in the fall on the stubble and then 
to work it under the surface. If it is necessary to wait until spring, it must 
be spread as early as possible before seeding, as soon as the soil has dried. 
Smaller doses (750 kg. to 1500 kg. per hectare) repeated about every five 
years, are more advisable than a single heavy liming, because, in the latter, the 
decomposition of the humus is so violent that the subsequent increase in the 
harvest is at the cost of a later production. It is said in practice that fer- 
tility is difficult to maintain on a lime-stone soil, because organic matter dis- 
appears rapidly. 

Naturally the amount of lime depends upon the soil. Tough clay soil 
will bear most, while great care must be used with poor sandy soil. Soils 
which are lacking in organic matter or have water standing on them, may 
not be limed at all. The results which become evident most quickly are 
given by a humus soil poor in lime ; — Sorrel (Rumex acetosella) indicates 
a scarcity of lime. Lime will act here splendidly as a fertilizer. 

If local lime deposits be used, such as possibly meadow-lime or marl, or 
the so-called waste lime (gas lime, lime ooze, lime ash), it is distinctly ad- 
visable, before using it, to let the air pass through in order to decom- 
pose it, or still better, to let it freeze. When using waste lime one should 
convince oneself first of all, by a simple experiment, that no injurious sec- 
ondary action can take place. According to Hoffman's experiments^, it 



1 Mitteilungen der Deutsch. Landwirstchafts-Ges. 1905, p. 367. 



238 

should also be taken into consideration that the more lime used, the less should 
fertilizing with potassium be neglected. In using stable manure, it is well 
to put the lime in the soil sometime before the manure is added. Bone meal 
should be avoided on soils containing lime. In the same way, it is not ad- 
visable to use ammonia and ammonia superphosphates together with lime. 
Pulverized quick lime should be used on binding, clayey soils ; lump or slaked 
lime on better loam soils. 

In regard to the need of lime by the different plants, IIofl"mann states 
that the Leguminoseae in general are distinguished as the most responsive 
to applications of lime, but that the Lupines and Serradella may be con- 
sidered as hostile to lime and sweet peas also do not like the direct use of 
lime or marl. 

In the use of marl also, the lime is the most active principle and hence 
it follows that a clayey soil, rich in humus, bears marling better than a poor 
sandy soil which in turn can be more benefited by a clay marl than by a 
lime or sand marl. The sometimes dreaded "impoverishment" from the use 
of marl will take place only if fertilizing with stable manure is delayed. The 
last is indispensable for all soils and especially for heavy ones in keeping the 
fields productive. No«mineral fertilizer can replace stable manure. 

The influence exerted by the lime contained in marl upon decomposition 
of the humus substances is illustrated very clearly by Petersen's^ experi- 
ments. He determined the amount of carbon dioxid produced in different 
soils by the process of decomposition with and without the addition of cal- 
cium carbonate. In using a heavy clay soil, known to be perfectly sterile, 
with 1.98 per cent, humus and 36 per cent, of its water holding capacity in 
water content, he obtained in 16 days 0.07 per cent, of the weight of the dry 
soil in carbon dioxid. On the other hand, the same soil under the same con- 
ditions with the addition of }^ per cent, of calcium carbonate, mixed in the 
clay as marl, yielded 0.20 per cent, carbon dioxid, or per liter of dry soil, 
without addition of lime, 0.9153 g. ; per liter of dry soil, with addition of ;^2 
per cent, lime, 2.6167 g. 

A leaf mould with strongly acid reaction consisting of 58 per cent, 
humus and 30 per cent, of the absorptive capacity in temporary water con- 
tent, yielded after 16 days, without and with the addition of t per cent, cal- 
cium carbonate (when the earth still gave an acid reaction) : per liter of dry 
soil, without the lime addition, 0.891 1 g. COo ; per liter of dry soil, with the 
addition of i per cent, calcium carbonate, 3.386 g. COo. 

With the addition of 3 per cent, calcium carbonate, the soil yielded 
5.3476 g. carbon dioxid, while the series of check experiments, free from 
lime, produced only 0.9664 g. COo. The addition of the lime, therefore, had 
caused 3 to 4 times as great a production of carbon dioxid, i. e., humus de- 
composition, as in the soil in an unmarled condition. 

Heiden, in Pommritz, summarizes thus the effect from the use of marl: 
The chemical action arises primarily from its content of calcium carbonate 

1 Jahresbericht f. Agrik. 1870-72. Landwirtsch. Versuchsstationen, Vol. 13, p. 155. 



239 

and consists in the hastened decomposition of the organic elements of the 
soil, in the combining of the free acids so injurious to plant growth, in the 
conversion of ferrous oxid into ferric oxid, and in bringing about the ab- 
sorption of the basic nutritive substances by the soil. The bases are held in 
the soil as hydrated silicates and as the salts of humic acid. In the absorp- 
tion of the bases by the humus body, these must be present combined with 
carbon dioxid. The lime promotes the formation of carbonates. Further, 
the mineral elements of the soil are decomposed, whereby the basic nutritive 
substances are freed and made accessible to the- plant. Every marl does not 
suit every soil, — clay soils, where possible, must have a lime or sand marl. 

Aside from these indirect advantages, the direct effect of the use of 
marl is shown in the addition of potassium, soluble silicic acid, magnesia 
and phosphoric acid, which, together with lime, are present in every marl. 

A few words should be added here as to the use of plaster or gypsum. 
Franklin's words, — "This has been plastered," are well-known. He wrote 
this in plaster on a clover field in order to recommend to his countrymen 
the process which had been known with great advantage by the Romans 
(Knop, Kreislauf des Stofifes) and the Greeks. According to Knop's experi- 
ments and those of Deherain and Liebig, a solution of plaster in soils con- 
taining absorbed potassium, frees it in the form of sulfate, while the lime it- 
self is precipitated. The method of spreading the plaster on clover plants 
freshly covered with dew or rain, recommended by experience, is found to be 
advantageous, since a solution of plaster is formed on the moist plants; 
dripping from them, it acts at once in the immediate vicinity of the roots. 
It thus rapidly becomes of advantage to the bacterial flora, for Pichard's^ 
researches and those of others show that plaster and other sulfates (potas- 
sium and sodium) exercise a most favorable influence on the process of 
nitrification. Plaster should be used in an unburned state and indeed for 
clover and lupines from 2 to 5 centner per acre in the spring. 

Although the influence of calcium hydrate or carbonate, favoring de- 
composition, was discussed above, it must still be emphasized, that, as shown 
by Wollny's" work, this is only of value when the substance is already de- 
composed and contains humic acid, while the addition of calcium on unde- 
composed organic substances rather hinders decomposition. This is especially 
true for calcium sulfate (gypsum) which comes under consideration as a 
conservation material for animal manure. In a mixture of quartz sand 
(300 g.), powdered peat (5 g.), and 60 ccm. water, Wollny^ found 

Volumes CO, in 1000 Volumes Soil air — 

without the addition of gypsum with the addition of gypsum 

■ 0.05 g. 0.1 g. 

CO. 3.194 3.029 2.713 



1 Annales agronomiques X, p. 302. 

- WoUny, E., Die Zersetzung der organischen Stoffe etc. Heidelberg-, Carl 
Winter, 1897, pp. 133 ff. 

3 Journal f. Landwirtschaft, 18S6, p. 263. 



240 

The addition of the plaster had accordingly reduced the loss in organic 
substances and also in nitrogen; i. e., had exercised an arresting influence on 
decomposition. The use of calcium compounds as a remedy against dis- 
eases, in which an excess of nitrogen comes under consideration, will be 
discussed under the individual cases of disease. 

3. THE DISADVANTAGES OF MOOR SOILS. 

The Acids in the Soil. 

Ramann^ explains as moors, — the formation of more moist regions in 
temperate zones, in which soils poor in nutritive substances, with an acid 
reaction, are covered with dwarfed bushes, grasses, mosses and peat-moss 
(sphagnum), and also lichens. 

The humic acids* act freely here, and cause the acid reaction of the 
soil. Acids are formed by the decomposition of the organic substances in 
the soil to which fungi as well as bacteria surely contribute a share (Cepha- 
losporium, Trichoderma, etc., according to Koning^). Formic acid, acetic 
acid, butyric acid, etc., are produced which decompose rapidly in well 
aerated soils. Besides these, however, the humic substances also form the 
still little known crenic acid with its salts (crenates) which, widely dis- 
tributed in soils and water, form a yellow, strongly acid solution, 
drying to an amorphous mass. While its salts with alkalis and alkaline 
earths are soluble, its ferric oxid remains insoluble. With the entrance of 
air aprocrenic acid is produced from it, the salts of which are either in- 
soluble or dissolve with difficulty. A great influence on the weathering and 
the transportation of the accessible mineral salts may be ascribed to these 
acids and their compounds^. Raw humus, peat and other soil substances 
with a strong acid reaction lose only a part of their acids even after lying 
sometime exposed to the air. Since even well aerated forest soil often 
shows an acid reaction, it may be concluded that scant oxidation either does 
not cause the production of the soil acids, or only at times produces them. 
We must consider here also the work of definite bacteria in this acid for- 
mation. Free acids are often absent in good soils, but poorer moor soils are 
frequently rich in them and become even poorer because extensive leaching 
and weathering processes constantly take place, due to the free acids. 



1 Ramann, Bodenkunde, 2nd. Edition. Jul. Springer. 1905. 

2 Koning-, Arch, neerland. sc. ex. et nat. 1902 II, 9, p. 34. 

3 Ramann, loc. cit. p. 144. 



* In the light of recent investigations on the nature of the organic matter 
of the soil it seems that we moist revise some of the older terminology. The term 
"humic acids" is rather to be regarded as a loose generic term applicable to a group 
of organic compounds found in the soil. — Vide: — 

Mulder, The Chemistry of Vegetable and Animal Physiology, trans, by From- 
berg, 1849. 

Schreiner, O. and Shorey, E. C, Bulletins 53, 74, and 88, Bureau of Soils, U. S. 
Department of Agriculture. 

Jodidi, S. L. .Tour. Amer. Chem. Soc. 34: 94. 1912; Jour. Franklin Inst. 175: 245. 
1913. 

(Translator's note) 



241 

In regard to the sensitiveness of our cultivated plants to free acids, 
Ramann cites Maxwell's^ experiments with i-io and 1-50 per cent, solutions 
of citric acid. He found that all the Cruciferae were quickly destroyed, the 
Papilionaceae more slowly. Grain suffered greatly, only the pearl millet 
and maize could withstand it. Tolf made discoveries in regard to humic 
acids, according to which seedlings suffer in acid moor soils. In the acid 
moor, the diffusion of the salt solutions is sharply arrested. According 
to Reinitzer and Nikitinsk, pure humic acids are unsuitable for the 
nutrition of bacteria and fungi. On the other hand, most of the higher 
plants can endure a moderate amount of these acids. We discover from our 
cultures of Ericas, Azaleas, Rhododendrons and other Ericaceae in moor soil 
that a number of plants indeed seem directly adapted to acid soils. 

The dark colored humus parts consist preponderately of Humin and 
humic acid (Ulmin, according to Mulder). The humus substance must be 
considered as a mixture of closely related bodies with and without nitrogen, 
which can be separated into two groups according to their behavior with al- 
kalis. The brown humin substances, insoluble in the most diverse solvents, 
swell up in alkaline liquids and pass gradually over into humic acids. The 
humic acids (their chemical composition is insufficiently known), containing 
possibly 59 to 63 per cent. C, 4.4 to 4.6 per cent. H. and 35 to 36 per cent. O, 
are easily dissolved in alkalis and are re-precipitated from their solutions 
by stronger mineral acids. If they are withdrawn from acid soils (moor 
soils) with alkalis or ammonia and precipitated with hydrochloric acid, a 
voluminous, jelly-like substance is obtain which, in drying, forms a brown 
or black amorphous mass. The humic acids are separated from their solution, 
by freezing, in the form of a dark colored powder, which gradually passes 
over again into solution. Ramann emphasizes the fact that humic acids are 
somewhat soluble in pure water, but not in water containing salts. The salts 
of the alkalis and of ammonia with humic acids are sokible in water, but 
not those of the alkaline earths (calcium and magnesium). Yet the latter 
also seems to become soluble with an excess of acids. Calcium humate will 
decompose quickly into calcium carbonate which will combine into new 
masses of humic acids. 

On an average, the nitrogen content of humus substances is greater in 
dry regions than in moist ones. By the advancing decomposition, the nitro- 
gen, which in organic combinations is accessible to plants with difficulty, is 
carried over into compounds easily absorbed. 

Raw Humus. 
Humus is beneficial and indispensible only wdiere, in pure deposits or 
mixed with the mineral skeleton of the soil, it is exposed to constant aeration 
and to sufficient moisture. Its chief action on plant growth does not lie in 
its nutrient content or in the carbon dioxid formed by its decomposition of 
minerals, but in its physical properties. 

1 Journ. Amer. Chem. Soc. 1898, 20, p. 103. 



242 

If humus is mixed with dense soils, they are loosened and made warmer 
and more easily worked. In sandy soils the humus acts as a hinder and in- 
creases the watef capacity, whereby the fluctuations in temperature become 
less marked. These favorable peculiarities, which arise from the mixing 
with mineral elements in the soil, disappear as soon as the humus is de- 
posited on the soil in impervious layers, i. e., is not broken up by abundant 
decomposition and the micro-organisms. In compact humus layers, the con- 
tent in free acids is almost always greater. The forest soils, which are most 
rapidly decomposed and worked up, are the best. In warm chmates the 
work progresses very quickly of itself. 

With a favorable humus decomposition, we find that in forest soils the 
porous forest debris, which forms the layers of litter, is not so thick and 
merges gradually into a friable, strongly decomposed, structureless humus 
layer. If in any region the factors contributing to decomposition are ab- 
sent, these layers of litter are retained, settle only gradually and become a 
firm, fibrous humus mass, which is deposited on the subsoil and remains 
more or less sharply separated from it. Such cases may be observed in poor 
sandy soils, especially those containing meadow ore. 

This process, in which therefore the organic substance acquires no 
earthy composition, will occur everywhere where conditions unfavorable to 
decomposition exist, — as, for example, when the air is excluded by water, or 
conversely, with too great drought in the hot seasons or in places exposed to 
constant strong winds. 

Our forest tracts, where heather (Calluna vulgaris), cranberries and 
huckleberries (Vaccinium) the pteris and aspidium brakes and the cushion- 
forming mosses grow, are most inclined to the formation of such fibrous and 
but shghtly earthy humus layers, the undecomposed elements of which are 
deposited in dense masses on the soil and in this way form the so-called 
"raw-humus." The upper layer of such raw-humus deposits still shows the 
interwoven structure of the plant debris, the lower layer, in which the plant 
parts are but slightly distinguishable from one another, has a fibrous dark 
humus substance interwoven with roots. In moist beech, pine and spruce 
tracts, such raw humus may become peat-like. 

Ramann (loc. cit. p. 162) states as his opinion of the change in the soil 
beneath a covering of raw humus, — that, besides the exclusion of air, the 
humic acids especially form the injurious factors. These act on the un- 
weathered silicate, decomposing it energetically, bringing into solution al- 
kalis and alkaline earths and, since at the same time the amount of acid 
solutions absorbed in the soil is slight, leaches the soil, i.e., the soluble sub- 
stances are carried down to greater depths. If raw humus lies on sandy 
soils, the grains of the uppermost layer appear to be strongly bleached and 
milk-white, the intermixed silicate rock is greatly weathered and usually 
transformed into white kaolin. The humus admixture still richly present on 
the upper surface decreases more and more from the top downwards so that 



243 

the soil becomes light gray in color and, because of this color, is called gray 
or lead sand. 

Below this Hght colored layer is found, sharply separated from it, a 
yellow to brownish looking soil, the deeper layers of which gradually be- 
come lighter. Here, the sand grains show mixtures of ferric-oxid or ferric 
hydrate. Then comes the white raw sand, still but little affected by weather- 
ing. The uppermost humus soil layer is found to be most weathered and the 
layer most impoverished by leaching. If the leaching of such an upper soil 
layer, under the influence of the raw humus deposited on it, be carried to a 
given stage, the action of the salts in the soil on the soluble humic acid must 
cease, the salts then remain in solution and can penetrate to the lower layers 
of the soil. If they come in contact here with soluble salts, they are precipi- 
tated and coat the separate soil grains with a structureless layer of organic 
substances. Under the microscope, I found the sand grains covered with 
brown, chart-like etchings. If this process keeps up, the precipitated or- 
ganic substances finally cement the separate sand grains into compacted 
layers below the lead sand, — meadozv-ore has been produced. 

'Meadov/-Ore. 

According to Ramann's explanation of the production of meadow-ore, 
given in the previous section, this is a humus sand stone. It occurs in var- 
ious forms and first of all as "Branderde" or "Orterde," which has a white 
easily pulverized form and shows a large content of organic substances. 
This is formed in rich soils which are but little changed unfavorably. The 
real swamp ore is a firm, stone-like, hard mass, deposited on easily pulver- 
ized or loose soil layers, with a medium content of organic substances 
and a brown to black color. This is the form most widely distributed in 
North Germany (Liineburger moor). Besides this, there is a lighter brown 
swamp-ore which is ver}^ firm and tough and holds but small amounts of 
organic substances. This is the hardest form, offering the greatest resistance 
to a working of the soil and frequently occurring in great thickness. 

In judging the processes of leaching, an analysis taken by Graebner^ 
from Ramann's- work may be useful. The swamp ore soil in the Main 
Forestry District Hohenbriick in Pomerania contained in its different 
layers : — • 

(a) Lead sand, which was 15 to 20 cm. thick and contained 1.05 per 
cent, of organic substances^. 

Soluble in Residue insoluble in 

Hydrochloric acid. Hydrochloric acid. 

Potassium 0.0076 per cent, of the soil 0.618 

(Sodium o.oiii " " " " " 0.167) 

Calcium o.oiio " " " " " 0.060 

Magnesia 0.0026 " " " " " 0.020 

(Manganous oxid 0.0032 " " " " " 0.060) 

Ferric oxid 0.0964 " " " " " 0.450 

Aluminum oxid 0.0268 " " " " " 0.650 

Phosphoric acid 0.0058 " " " " " 0.043 

Total content except silicic acid. 0.1645 2.068 

1 Paul Graebner, Handbuch der Heidekultur. Leipzig, Wilh. Engelmann. 1904, 
p. 194. 

2 Die Waldstreu, Berlin, 1890, p. 30. 

3 Ramann in his "Bodenkunde" 1905, p. 166, gives the same analysis without 
the elements enclosed in parantheses. 



244 

(b) Swamp ore, 5 to 8 cm. thick with 7.28 per cent, of organic sub- 
stances : 

Soluble in Residue insoluble in 

Hydrochloric acid. Hydrochloric acid. 

Potassium 0.0178 per cent, of the soil 0.754 

(Sodium 0.0033 " " " " " 0.360) 

Calcium 0.0194 " " " " " 0.170 

Magnesia 0.0137 " " " " " 0.028 

(Manganous oxid 0.0044 " " " " " 0.047) 

Ferric oxid O.1936 " " " " " 0.690 

Aluminum oxid 1.5266 " " " " " 2.320 

Phosphoric acid 0.2956 0.042 

Total mineral substances except 

silicic acid 2.0744 4-4^1 

(c) The yellowish brown sand underlying the swamp ore: 

Soluble in Residue insoluble in 

Hydrochloric acid. Hydrochloric acid. 

Potassium 0.0085 per cent, of the soil 1.103 

(Sodium 0.0213 " " " " " 0.528) 

Calcium 0.0254 " " " " " 0.225 

Magnesia 0.0401 " " " " " 0.064 

(Manganous oxid 0.0068 " " " " " 0.026) 

Ferric oxid 0.3448 " " " " " 0.760 

Aluminum oxid 0.4000 " " " " " 3-2IO 

Phosphoric acid 0.0281 " " " " " 0.043 

Total mineral substances except 

silicic acid 0.8750 5-959 

We perceive from the above figures that, by leaching, the lead sand has 
not only lost in soluble substances, but that the greatest part of all the 
rock debris containing nutritive substances has been decomposed by 
weathering and being washed deeper down. It is therefore a fact that cer- 
tain soil layers in forests and in open moors (usually formed from such soil 
layers) become impoverished. This is very significant agriculturally if the 
impoverishment exceeds the supply of nutriment furnished by weathering 
and the annual rain fall. 

Meadow ore must be distinguished from the real swamp ore ; the for- 
mer is insoluble in an acid solution, such as hydrochloric acid, while the 
swamp ore is abundantly dissolved. 

Especially in humus moor soils, where the deposition of raw humus 
leads to the formation of swamp ore, do two chief injurious factors come 
under consideration : — the lack of oxygen due to the density of the soil and 
the content in humic acids. The processes taking place, with an exclusion of 
oxygen, have been considered in another place (for example, p. 99). 
We have here to take only the humic acids under consideration. Graebner 
pays the desired attention to this point^. Continuing Wolf's^ investigations on 

1 Log. cit. p. 228. 

2 Tagebl. Naturf, Vers., Leipzig, 1872. 



245 

the wilting of the leaves and their ultimate death, resulting from the de- 
tention of the plant roots in water excessively charged with carbon dioxid, 
Graebner cites Maxwell's experiments^ with citric acid and those of Tolf 
and Blank with humic acids, all of which lead to similar results. This is the 
place to record Ramann's statement as to the cause of retarded diflfusion in 
acid soils. Either the colloidal composition of the moor-substances can re- 
duce the capacity for diffusion and the colloidal substances are precipitated 
by neutralization with lime, or some direct action of the humic acids is 
present. If one thinks of the discoveries showing the influence exerted by 
slight acid increases on the protoplasm", whereby its currents are arrested, 
one must consider the direct action of the acid to be of the chief importance. 
Special proof already exists of the retarding of transpiration by acids (tar- 
taric, oxaHc, nitric and carbonic acids, etc.) and its hastening by alkalis 
(potassium, sodium, ammonia) ^ It can therefore be said, with Schimper, 
that plants in a strongly acid soil will suffer from physiological drought even 
in the presence of abundant water. To this must be added that the great 
power of humus to retain water makes the mechanical withdrawal of the 
water from the soil particles much more difficult for the roots than if in 
sandy soil. Plants are found to wilt in peaty soil or loam with a percentage 
of water sufficient to keep them perfectly fresh in sandy soils, as Sachs'* 
experiment has already shown. 

All these injuries due to the soil find expression most of all in the culti- 
vation of pines, which subject Graebner^ has treated with especial thorough- 
ness. He found in young pine plantations, which had grown tolerably well 
for some years, that the shoots formed in May at first developed normally, 
but, with the appearance of the summer drought, became grayish green in 
color. If the dry period continued, the shoots begin to curl, the needles of 
the previous year became blunt and brown and in many cases the little trees 
dried up in a few weeks. By digging in the soil, it was found that swamp 
ore had been formed below the roots or even around the still rather slender 
ones. 

To supplement his description, Graebner pictures in the figures here 
reproduced root development on swamp ore soils. We see in figure 29, that 
the strongest and longest roots are spread out not far below the surface of 
the soil and parallel to it, so that its nutrition must take place through the 
raw humus and the lead sand, which is poor in nutritive substances. Since 
root development is greater in solutions poor in nutritive substances than in 
concentrated solutions, this results in a wide reaching out of the root 
branches, which, in the present case, according to Graebner, seem several 
meters long and but little branched. The aerial axis, however, is scarcely a 



1 Journ. Ann. Chem. Soc. XX (1898) p. 103. 

2 Pfeffer, Pflanzenphysiologie II Vol. 1904, p. 798. 

3 Pfeffer, Pflanzenphysiologie I Vol. p. 231. 

4 Sachs, Handb. d. Exp.-Physiol. Leipzig-, 1865, p. 173. 

5 Graebner, R., Handbuch der Heidekultur, Leipzig, 1904, W. Engelmann, p. 231. 



246 



meter high. Poverty in nutritive substances in combination with the lack of 
moisture, easily becoming great in lead sand, are the causes of an ultimate 
blighting at the tops. 

Figure 30 shows the root growth of an oak. The oak was planted after 
the layer of swamp ore had been broken through artificially. But this layer 
of swamp ore had later re-united and the portion of the root in g, nearly 
shut away from an air supply, had practically stopped growing. No mycor- 
rhiza, or scarcely any, could be found on this part of the root, 

Graebner attaches the fol- 
lowing significance to such 
phenomena. If the swamp 
ore is deposited below the 
roots, the earth lying above it 
is naturally exposed to great 
fluctuations in moisture, and 
in times of drought becomes 
so dry that the plants die from 
a lack of moisture. In cases 
of this kind, however, the 
plants forming their roots en- 
tirely in the lead sand, exhibit 
a very weak growth, grad- 
ually making itself evident by 
short, yellow needles. If the 
swamp ore, however, lies di- 
rectly around the roots, which 
are about as large as knitting 
needles, and have penetrated 
in to the better soil, it presses 
against them, causing knotty 
swellings. This takes place if 
the roots reach the better sub- 
soil through an" opening in the 
swamp ore layer. Such me- 
chanical constrictions disturb 
further root growth. The tree 
is therefore essentially dependent on the roots lying above the swamp ore 
layer. Growth and vital activity are normal during the spring dampness, but 
all activity stops if a hot summer dries out the soil. Graebner found the root 
lips shrivelling, turning to resin or dying entirely. In larger trees, with a 
renewal of moisture, time and material are necessary for new root growth. 
This loss in time and substance becomes evident in the growth of the aerial 
axis and, in combination with the results of the period of drought, causes in 
great part the weak growth of the moor pines. The plantations improve as 
soon as the fluctuations of moisture are less extreme. 




Fig 29. "A meadow ore pine" from the Lune- 
burger moor, grown after the formation of the 
meadow ore. 

r raw humus, b lead sand, o meadow ore. Below the meadow- 
ore the yellow sand begins. (After Graebner.) 



247 

Usually pines on high moor soil develop a very crooked form"^. Yet 
ihe seeds of these crippled pines, after the moor has been drained dry, grow 
into erect trunks. Schroter and Kirchner- also state that, on too wet places 
in the high moor, Pinus montana makes a reduced cripple growth 
("Kusseln"), but recovers after the water has been drained fi:om the soil. 
Our pines form such ("Kusseln") also on wet meadows. In the cases I 
have observed, this form of growth was produced by the resinification of the 
terminal bvid of the main shoot, because of insect and fungus injury; there 
then develops below this bud a number of shoots which remain short (and 
in part some rosette 
shoots). 

Plgure 31 shows a 
pine 48 years old which 
came from the Liinebur- 
ger moor and which Dr. 
Graebner most kindly 
placed at my disposal. 
The height of the whole 
tree, — including the tops 
and measured from the 
root neck up, amounted 
to 74 cm. ; the length of 
the trunk up to the first 
branch, 39 cm. ; the girth 
of the trunk below the 
lowermost branch, 8 :3 
cm. ; the average length 
of the needles, 2 cm. The 
foliage of the whole tree 
is very sparse. The 
needles have remained 
only on the latest shoots, 
all the older ones have 

fallen. The branches are greatly thickened in places and cracked open 
as a result of injury from frost. The perpendicularly growing tap 
root is 8 cm. long to its place of horizontal bending; the largest horizontal 
root branch, 18 cm. The branch growth is sparse and the branches have 
sharp angles (k) and often dead tips (a). These sharp angles or bow-like 
curves (k) arise because the branches and the main trunk have received one- 
sided, canker-like frost wounds to which correspond an increased wood for- 
mation and a stretching on the opposite side. Greater frost wounds, extend- 
ing over more than half the circumference of the axis, are found at / and /'. 




Fig-. 30. An oak from the Luneburgei- moor planted 
after the meadow ore had been broken through. 
The layer of meadow ore had closed later. 

r raw humus, b layer of sand 20 cm. thick, o meadow ore. 
g- yellow sand. (After Graebner.) 



1 V. Sievers, Ueber die Vererbung von Wucksfehlern bei Pinus silvestris. 
Porstl.-naturwiss. Zeitschr. 1898. Part 5. 

2 Lebengeschichte der Bliitenpfianzen Mitteleuropas, Part III, 1905. p. 222. 



24B 

In figure 32 f on the main trunk is reproduced in natural size, in order to 
show that, like "open canker," the wounded surface consists of many very 
small, over-growth edges of different years which recede like terraces. 

In accordance with the paltry branch growth in figure 31, the root is 
also small ; it cannot follow its natural tendency to send its tap root downward 




Fig. 31. A moor pine with flatly extended roots from the Luneburger moor. (Orig.) 
a dead tips of branches, k parts of the branch which have grown out at sharp angles, k' parts of the branch 
curved like bows, / frost wound where the branch leaves the trunk, f frost wound m the form ot an open 
canker with a distinctly limited wood body, h roots which had grown against the layer of meadow ore. 

perpendicularly (compare figures 5 and 6, p. 95), but must extend 
its root branches in the upper soil layers and moss cushions. Part of the lowest 
root branches are partially bent upwards at a sharp angle, probably because 
they have met with a layer of swamp ore or some similar impenetrable body. 



In his study of the high moor of Augstumal in the Memel delta, 
Weber^ gives very interesting illustrations of the crippled forms of pines, 
corresponding to the Finns sihesfris f. turfosa, Willk. Here he describes 
also the crippled birches, v^hose roots, like 
those of the Scotch fir, always showr splen- 
didly developed mycorrhiza. The trunk, 
usually only a few centimetres thick, is most- 
ly bent and knarled, and covered below with 
a seamed hark, a very striking feature in such 
small trees. To this it should be added that 
these small birches usually only about 1.5 
m, high form a well set top. On an average, 
the main root penetrates only 15 to 20 cm. in- 
to the soil, then bends to one side, to run 
parallel with the surface. The roots, spreading 
sidewards, attain to 3 to 4 times the length of 
the trunk. The vegetation on the high moor 
is best characterized by a specimen of Betula 
pubescens described by Weber". The upper 
trunk, which had white rot at the top, was 
1.8 m. high; the wood from which the bark 
had been removed was possibly 34 mm. in 
diameter above the root neck and had 51 
annual rings, the last eleven of which alto- 
gether were only 0.9 to 2.6 mm. wide. The 
little tree was just beginning to become 
blasted at the top and was overgrown for 30 
cm. above the root neck with Sphagnum 
medium and >S. acutifolium. 

In cultivation, it is not only necessary to 
break through the swamp ore layer, but also 
to bring it up to the surface of the soil. In 
the air, it decomposes to a brown sand, 
which gradually becomes lighter in color be- 
cause the organic elements have weathered. 
Freezing the swamp ore hastens this process 
greatly. The decomposition usually takes 
place more quickly when the content in or- 
ganic substances is higher. Brown colored 
swamp ore (rich in humus) is usually de- 
composed in a year; on the other hand, 
the light colored (which is poor in humus) 




Fig-. 32. Canker-like, wounded 
place on the moor pine. 

c the (deepest lyiiier) wood centre, 
/ edges of the wound rising like ter- 
races in which the most recent, j, are 
the most rolled back and the old bark, 
r, covering it, which is breaking loose 
in squarrous pieces, 7v dying, outer- 
most edge of the wound, / lichen 
growths. (Orig.) 



only after 2 to 4 years. 



1 C. A. Weber Ueber die Veg^etation und Entstehung- des Hochmoors von Aug- 
stumal im Memeldelta, etc. Berlin. Paul Parey, 1902, pp. 40 ff. 

2 Loc. cit. p. 47. 



2$0 

Poisoning of the Soil by Metallic Sulfur. 

In considering factors injurious to plant growth ferric sulfid as pyrites 
(and rhomboidally crystallized as markasit) must be noticed primarily since 
it is one of the most widespread precipitates produced in the formation of 
moors. Ferric sulfid is found less in moors themselves than in the imder- 
lying sand and on the line between the organic deposits and the subsoil. If 
pyrites weathers, there is produced by oxidation and absorption of water sul- 
furic ferrous oxid, — ferrous sulfate, copperas, and free sulfuric acid (FeS^-l- 
70+H,0=FeSo,4-H2SOJ . 

The ferrous sulfate oxidizes with the formation of basic salts to ferric 
oxid. In the presence of sufficient amounts of calcium carbonate, calcium 
sulfate (gypsum) is produced. If ferrous carbonate occurs, it passes over 
into ferric oxid or ferric hydrate with the loss of carbon dioxid and the 
taking up of oxygen. As is well known, the ferric hydrates cause the yellow 
to brown color of the soils and are able to absorb gases (carbon dioxid, nit- 
rogen, etc.) to a very marked degree. Among them is the brown clay iron 
ore (limonite Feo[OH](;) which cements together the surrounding sand^ In 
moor regions, however, the layers containing pyrites are often not oxidized 
at all ; because of the presence of water and the strongly reducing action of 
the moor substance they cannot obtain any oxygen. 

The most disasterous effect of the iron sulfid is its inhibition of the com- 
bining of the bases present in the soil and the free sulfuric acid formed by 
weathering. As a rule, calcium carbonate is present in the soil, so that gyp- 
sum can be formed, often alum or magnesium sulfate are also produced. An 
excess of the last can act injuriously. When experimenting with an exces- 
sive supply of alum, I found spotted necrosis appearing in barley. However, 
if the bases are absent, the free sulfuric acid will act directly as a plant 
poison. 

If, in improving the soil, the layer containing the pyrites is brought to 
the surface, the soil will at first remain infertile. 

Minssen- shows that at times the upper layers of the moor also contain 
iron sulfid. In a sample from Silesia he found 7.286 per "cent, of the dry 
substance of the surface soil to be sulfuric acid, soluble in water, 3.940 per 
cent, ferrous sulfate and 3.346 per cent, free sulfuric acid and approximately 
twice as much in the deeper layers, aside from great masses of still un- 
weathered iron bisulfid. The top of the sulfate here analyzed was later re- 
moved 62 cm. deep, so that the lower layers richly impregnated with iron sul- 
fid were laid bare. The oxidation of the pyrites gave such large amounts of 
compounds injurious to vegetation that any agricultural use of the moor 
within a conceivable time seemed impossible. Such a case shows the neces- 
sity for the use of foresight in opening up lowland moors. 



1 Ramann, Bodenkunde, 1905, p. 87. 

2 Mitteilung'en d. Ver. z. Forderung- der Moorkultur im Deutsch. Reich, 1904. 
No. 1. 



The question as to the nijuriousness of the black colored water floimng 
on to the meadozvs from the alder bogs of forests has been treated in detail 
by Klien^. In one especial case which gave rise to complaints against the 
forestry commission, the water coming from the forest was viscid, brown and 
at times smelled bad. In 100,000 parts, it contained 31.28 parts organic sub- 
stances (humic acids, etc.) and 17.59 parts mineral substances, among others 
7.81 parts calcareous earth, 3.07 parts ferric oxid, etc. The humic acids 
formed the injurious factor here. In similar cases it depends on the kind of 
soil overflowed by such bog water. It will be especially injurious if it flows 
over ferruginous soils or those with a clay subsoil, while a soil rich in lime 
can more easily withstand overflowing from the alder swamp, such as oc- 
curs in spring floods, because of the hastened decomposition of the hurhus, 
peculiar to such a soil. Nevertheless such water should be avoided for irri- 
gation and back water. 

The formation of ferruginous sand depends on the precipitation of fer- 
ric hydrate and iron silicates. Mixtures of ferric hydrates with varying 
amounts of ferric silicates and phosphates also give the so-called meado'di- 
ore. This combination occurs in moors, standing bodies of water and other 
places, where water containing iron comes in contact with the air, together 
with the co-operation of bacteria (iron bacteria according to Winogradski)-. 
One is inclined of late to lay stress on the co-operation of the micro-organ- 
isms'. 

Susceptibility to Frost of Moor Vegetation. 

In moor soils which have been brought under cultivation, their especial 
sensitiveness to frost as compared with other kinds of soil has been proved 
by repeated experiments. In this, important diflrerences are found if the 
moor soil has a sandy covering or if it is mixed with sand. Wollny* found 
in his experiments that the latter is more fertile than the former, in which 
the ground water was higher. Instead of the sand, a covering with clay has 
also been proved to be beneficial. In meadow cultivation when too much 
water has been removed, Fleischer"' recommends covering with sand, rich in 
feldspar, or loam, or clay to avoid too great drying out. Jungner" gives fur- 
ther examples from the province of Posen. In them moor fields which had 
not been covered with soil containing clay, showed also a second total freez- 



1 Klien, Die nachteilisre Einwirkung- des aus Eller-Bruchen und Torfmooren 
kommenden schwarzen Wassers auf die Wiesen. Konigsberger land- und forst- 
wirtschaftliche Zeitung 1879, No. 28; cit. in Biedermann's Centralbl. f. Agrik- 
Chemie, 1880, p. 568. 

2 Winogradski, Ueber Ei&enbakterien. Bot. Zeit. 1888, p. 260. 

3 E. Roth, Die Moore der Scliweiz, unter Beriicksichtigung der gesannten Moor- 
frage. Leopoldina, 1905, No. 3, p. 34. 

4 Wollny, Untersuchungen liber die Beeinflussung der physikalischen Eigen- 
schaften des Moorbodens durch Mischung und Bedecl<ung mit Sand. II. Mitteil. 
Porsch. a. d. Geb. d. Agrik.-Physik. 20, 1897-1898, p. 187. 

5 Fleischer, M., Ueber die zweckmafsige Behandlung von Moorwiesen; cit. 
Biederm. Centralbl. f. Agrik.-Chcmie, 1888, p. 137. 

6 Zweiter Jahresber. d. Sond.-Aussch. f. Pflanzenschutz fiir 1904. Arbeit, d. 
Deutsch. Landw.-Ges. Part 107, Berlin, 1905, p. 61. 



252 

ing back of potatoes and pasturage, while those which had been covered 
had suffered no especial injury. 

This discovery indicates that we have to look for the chief period of- 
injury in spring, so far as frost phenomena in moor soils are concerned. In 
cultivating trees this becomes clear, if we consider that the humus soils in 
cold seasons usually contain an excess of moisture. The fine pored humus, 
saturated with water, will cool more slowly in the fall than do soils less rich 
in water, but will warm up much more slowly in the spring. However, the 
longer the roots are in a warm location, the longer they remain active and 
the more water will be forced up into the aerial axes. Trees growing poorly 
on moor soil with its diluted nutrient solutions start the winter with a large 
water content in their tissues. The more water the tissues contain and the 
less cytoplasm, the more susceptible are they to frost, no matter whether the 
effects of winter or spring frosts are concerned. Hence the frequent and 
great injury from frost in moor pines, as is shown in the example from the 
Liineburger moor. 

For short-lived field plants the most disasterous are the spring frosts 
which are produced in rays of cold. This may be easily recognized from the 
fact that the phenomena of discoloration produced on the leaves and stems 
by the cold are abruptly cut off, if such a part of the plant is partially cover- 
ed by overlying leaves. 

It is now pertinent to ask when cold, due to radiation, will be greatest 
and how much of it is due to evaporation. If both factors become effective 
to a high degree, the air layers close above the surface of the soil will be 
noticeably colder than the average temperature. Polis^ has proved such a 
lowering of the temperature of the air layers above a covering of snow. This 
will be the greater, the less the movement of the air. Hence May frosts in 
still, clear nights. The moor soils and those bordering on moors with their 
wealth of water will evaporate strongly in the early spring when the soil and 
subsoil have not been warmed through, even if, as cultivated land, they have 
been mixed with sand and accordingly more cooled down. Evaporation will 
also be still more increased by the dark color of the soil, as WoUny's- experi- 
ments show. Covering with a layer of sand from 6 to lo cm. deep acts as a 
preventive. Then but little water can reach the sand from the humus layer 
and, correspondingly, only small amounts will.be evaporated. For the same 
reason the dead layer also acts as a protection against drought. One dis- 
advantage of the sand covering is found when fine, surface-rooting grasses, 
are sown which are easily stunted in sand, poor in nutrition^. 

If the cultivation of fruit trees on moor soils is involved, the following 
may be recommended for protection against frost: (i) The planting 
of trees on the west and southwest side of the orchard, in order to modify 
the temperature differences in spring. The bark cracks almost without ex- 

1 Meteorologische Zeitschr. 1896, Part I. 

2 Blatter fur Zuckerriibenbau, 1899, No. 9. 

3 Mitteil. d. Ver. z. Ford. d. Moorkultur, 1895, Nos. 5 and 6. 



253 

ception on the sides turned towards these pohits of the compass and the nor- 
mal phenomena of loosening bark scales (for example, on plane trees) also 
begin earlier and to a greater extent on those sides of the trees. (2) A 
strong liming and supply of Thomas slag with a sufficient provision of other 
nutritive substances. (3) Above all, however, those varieties of fruit should 
be chosen, which endure moor soil. Huntemann^ recommends the common 
bouse plum, from practical experience. Of apples, the following have stood 
the test : Bosbook's Beauty, Golden noble, Double pigeon. White winter 
apple, Orleans, Parkers Pippin, Purple red Cousinot. The winter Yellow 
Pearmain, Gravenstein, Prince and Alant apple should not be planted, since 
they are too susceptible to frost and also to canker. According 
to the experiences of Mr. Klitzing, a nurseryman, the following apple var- 
ieties are adapted to cultivation on moor soils,- — red Eiser apple, Burchardt's 
Reinette, and Cludius' Autumn apple. Of pears, he recommends Charneux 
Delicious, St. Germain and New Poiteau. If cherries are tried at all, 
sour varieties should be chosen rather than sweet ones. 

The Usefulness of the Spruce. 

In considering forest plantations on moist soil, we only reiterate our 
opinion that it is a mistake to plant pines so extensively as is now done. The 
example cited on p. 248 from the Lilneburger moor shows clearly enough 
what disadvantages arise. If they are not so distinctly noticeable in other 
places and especially if frost injuries do not appear so sharply, yet a weaken- 
ed growth is always induced, which sooner or later becom.es evident. 

For the plains in northern Germany we should return to the spruce. 
We use the term "return," for Conwentz- has actually proved that often, in 
moor regions, spruce was the original covering. Even now in Pomerania 
and Hanover, even on the Liineburger moor, original spruce woods are 
often still in existence, and the various cases especially studied by Conwentz 
give excellent indication that the spruce is still found in a developmental 
stage, resembling the primeval forests, on soils where wide stretches are 
covered with peat moss and the moisture in usual years makes access to the 
soil impossible. 

This opportunity should be taken to consider the layering formations of 
spruces, which at any rate may be found only in forests not touched by for- 
estration and it is advisable on this account to preserve accounts of especially 
good examples of increase by means of layering. Hence an illustration and 
description of a spruce family should be given here, which has been observed 
in the vicinity of the city Kragero on the south eastern coast of Norway 
(see Fig. 33). Schiibeler^ describes it as follows. The parent trunk, which 
stands at the foot of a hill, had a height of approximately 9.4 m. and, about 

1 Huntemann, Das Erkranken der Obstbaume auf Moorboden. Mitt. d. Ver. z. 
Ford. d. Moorkultur. 1898, No. 7. 

2 Con-wentz, H., Die Ficlite im norddeutschen Flachland. Berichte d. Deutsch. 
Bot. Gesellschaft 1905, Part 5, p. 220. 

3 Schiibeler, F. C, Die Pflanzenwelt Norwegens. Christiania 1873-75, p. 164. 



254 

6.6 cm. from the ground, a circumference of 94 cm. At a height of 31 to 36 
cm. three branches left the main trunk, and took root in several places. At 
a distance of 1.6 to 2.5 m. from the present trunk, six regular spruces have 
gradually developed with a height of 2.5 to 4.7 m. 




Pig. 33. A spruce family produced by natural layering-. Three of the branches at 

the base of the trunk have rooted again in several places and their buds 

have there developed into secondary trunks. (After Schiibeler.) 

The spruce stands by itself in its easy formation of adventitious buds, 
giving rise to gnarls, and in the ability of parts of its aerial axis to form 
roots quickly. To be sure Schiibeler (loc. cit. p. 163) has also observed 
rooting in low branches of Juniperus and also in Taxus haccata, v^hich have 
been bent to the earth, and certainly such conditions will occur also in other 
conifers which grow well from cuttings. But cases of this kind will always 
remain isolated. 



255 

The capacity for increase, explained here by means of the one example, 
has a greater significance in moor regions, where the spruce will have to be 
grown as the only possible means of forestration. 

Only very few varieties of conifers possess this facility for forming 
layers and developing new regular top growth from lateral sprouts. Gar- 
deners make abundant use of this peculiarity in propagating young individ- 
uals from cuttings. In other conifers, cuttings from the lateral branches 
retain the structure of laterals and do not form handsome trunks. The 



■X7 











Fig-. 34. Oak from Rogau (Upper Silesia) with a formation of sinliers. (Orig.) 

genus Araucaria also has a great tendency to form head shoots and this is 
often shown in individual lateral branches, which remain on the parent 
plant, when the top shoot has been lost. 

In connection with this layering formation of the spruce, occurring on 
damp soils, we give in figure 34 the sketch of a case of root formation from 
a branch of an oak, which has been observed only once. In the 8o's of the 
last century, I had an opportunity in the castle park at Rogau (Upper 
Silesia) of seeing the very hollow trunk of an old oak which stood on a low 
lying meadow, liable to be overflowed by the Oder at flood time. The tree 



256 

had already lost most of its leaves on the lower branches. The upper parts 
of the two lowest branches, probably at some time bent down intentionally, 
lay deep in the earth, but their tips had been turned upward. At the point 
where the branch was bent (at the right in the figure) a strong root was 
traceable which might have been produced when the still young branch tip 
was covered with silt by the first floods. The increased nutrition, produced 
by this root, showed itself in the development of a considerable number of 
younger shoots, resembling an independent bushy growth. I noticed noth- 
ing especial in the vigorous spruce plantations standing at some distance. 

Changes in Moor Soil Through Cultivation. 

One must determine finally how far the injurious factors of humus 
soil show in cultivation and what changes it undergoes with cultivation. 
"Sanding" has been discussed already. Fertilizing comes next under con- 
sideration, since the nutriment content especially in highland moors is so 
scanty that only plants needing little nutriment and highly resistant to humic 
acids thrive there (Sphagnum, Eriphorum, many Carex varieties, Calluna, 
etc.). All fertilizers must act, first of all, by increasing those micro- 
organisms which can decompose the soil, since in soils containing humic 
acid, the bacterial flora is very scanty, Fabricius and v. Feilitzen^ gained 
much information on the methods to be used in increasing the bacterial flora 
of moor soils. Stalstrom- had already determined that draining the water 
from moor soil, very poor in bacteria, naturally will increase the number of 
organisms. This is especially significant for highland moors, since they have 
not nearly as many bacteria as the lowland moors ; — a fact related to the 
scanty nitrogen content of the highlands. Moor soil mixed, with clay or im- 
proved by fertilizing, has a higher bacterial content. The bacterial flora re- 
mains almost exclusively in the upper soil layer, 15 to 25 cm. thick, Fab- 
ricius and V, Feilitzen also tested the moisture content in the upper soil layer 
and found that, in uncultivated highland moors, this fell only from 90 to 87 
per cent, by draining, while, on the other hand, it could fall to about 64 per 
cent, with other cultural measures. These consisted in mixing the friable 
soil with sand, with the result that vegetation of a difi:'erent character de- 
veloped. The soil temperature was lowest on the virgin moor. Simple 
draining exerted but little influence (-|-o.3°C.), but cultivation gave a per- 
manent increase of almost 2°C. In regard to the chemical composition, it 
was found, as was to be expected, that the calcium content was very small 
in natural highland moors and the nitrogen content equally scanty, while in 
the lowland moors the latter was found to be satisfactory. The disappear- 
ance of the humic acids through cultivation is very interesting. In the 



1 Fabricus, O., and Hjalmar von Feilitzen. Ueber den Gehalt an Balcterien in 
jungfrauhchem und liultiviertem Hochmoorboden auf dem Versuchsfelde des 
Schwedischen Moorliulturvereins bei Flaliult. CentralbL f. Bakteriologie etc. II 
Section, Vol. XIV, p. 161. 1905. 

2 Om lerslagningens betydelse. Finska Mosskulturforeningens irsbok. 189S. p. 44. 



257 

natural highland moor the content amounted to more than 2 per cent, and 
through sanding, liming, and fertilizing became reduced to possibly 0.3 per 
cent. 

These same investigators found the bacterial flora only sparsely de- 
veloped, as a result of the acid soil in the highland moor, and also but little 
increased by draining. On the other hand, a great increase was found after 
sanding, liming and fertilizing together with the necessary attendant work- 
ing of the soil. Sand introduced new bacteria, stable manure furnished rich 
nutriment of such a kind that the bacterial content become as great as in a 
lowland moor under the same cultural conditions. In both the bacterial con- 
tent increases and falls directly with the soil temperature. 

The experiences of practical workers disagree greatly as to the use of 
stable manure. In many places there has been failure. But, on the other 
hand, reports are found, which determine a very beneficial effect from stable 
manure even on moors with a large nitrogen content, as Count Schwerin 
reports^. 

This contradiction can be explained as follows. Even in moors, which 
contain nitrogen in excess, fertilizing with stable manure can act very bene- 
ficially if the moor is but little decomposed, the nitrogen in it therefore being 
probably still in a form not easily taken up (for example in organic com- 
pounds). On cultivated moors, however, the yields ^fter fertilization with 
manure are actually poor and the weeds grow in excessive quantities because 
an excess of nitrogen probably makes itself felt, due to the addition of ma- 
nure without the sufficient counterbalance of a phosphate and calcium supply. 

Potassium is a factor primarily involved in the cultivation of moors. 
This holds good also for moor-meadows, on which, however, a good hay 
harvest, according to M. Fleicher-, requires the addition of phosphoric acid 
(Thomas slag) besides potassium. (In this connection, he warns against 
over-fertilizing if the ground zvater level does not lie deeper than 20 to 40 
cm.). The form in which the potassium is given may also be determinative 
in the majority of cases, for Tacke^ obtained the best results for potatoes 
with potassium chlorid. While the tubers contained 17.67 per cent, starch 
without fertilizing and 17.02 per cent, when fertilized with kainit, and only 
16.48 per cent, with karnallite, they contained 18.02 per cent, with the ad- 
dition of potassium chlorid. The fertilizers were added in the fall ; spring 
fertilizing reduced the quantity and quality of the tubers. Hensele* 
found in his potato cultural experiments that kainit on meadow 
moor soils considerably repressed the starch content of the potatoes. 
In comparative cultures on mineral and moor soils, the yields from the for- 
mer were larger and the starch content of the moor potatoes never equaled 
that of the tubers from a mineral soil or that of the seed. 



1 Mitt. d. Ver. z. Ford. d. Moorkultur, 1895, Part 6. 

2 Milchzeitung 1887, No. 8. 

3 Mitt. d. Ver. z. Ford d. Moorkulture 1895, No. 6. 

4 Hensele, J. A., Bericht der Moorkulturstation, "Ei'dinger Moos," 1900-01. Cen- 
tralbl. f. Agrik.-Chemie, 1903, Part 3. 



258 

In regard to the injuriousness of spring fertilising, reference should be 
made to the reports of the General Assembly of the Society for the Advance- 
ment of the Cultivation of Moors^ Here it is especially emphasized, that 
kainit and Thomas slag must be scattered in the fall because spring fertiUz- 
ing reduces the sugar and starch content in vegetables which require hoeing. 
For Thomas slag, the fall fertilizing is said also to be more beneficial because 
the acid of the moor can then act as a solvent for a longer time. Chili saltpetre 
in cultural experiments had decreased the sugar content in edible roots about 
1.5 per cent. The preceding crop also seems to have an influence on moor 
cultures, as is shown by a case from the province of Posen-. There sugar 
and late grown fodder beets became diseased when grown after mustard. In 
regard to beet cultivation, Hollrung^ arrives at the conclusion that pure moor 
land should be avoided entirely and even that which has been sanded should 
be used only with care. 

Rotten Bark. 

Up to this point we have learned to recognize the characteristic starved 
types of growth on acid moor soil ; these are due not only to the scarcity of 
nutriment but to moisture conditions as well, either a lack of water 
arising from the fluctuations in the subsoil, or an excess. These manifest 
themselves in older trees by a greater formation of bark, when high cushions 
of heather and moss surround the base of the trunk. These dense cushions 
store up water, in part retaining that of the moor soil, in part collecting that 
of the atmosphere, and in this way forming a moist felt constantly growing 
up higher around the base of the trunk. Such damp cushions decrease the 
temperature variations necessary for the pushing off of the old bark scales. 
However, they hinder the supply of air especially and cause the decom- 
position of those cell layers in the bark scales, which are especially loosely 
constructed, into a deep brown mass, powdery in a dry condition and slimy 
when very damp, which is called "rotted bark." In these are found the 
brooding places of many animal and vegetable organisms which carry on 
and hasten decomposition. 

An investigation of the younger layers under the old bark scales throws 
light on the production of these rotted masses. One of the pieces of bark 
furnished by Dr. Graebner from the Liineburger moor was 3.5 cm. thick and 
differed from equally old, healthy bark in that it could be peeled with un- 
usual ease into separate layers varying in thickness. The upper surface of 
the different bark layers, as they fell apart, was rough like a relief map and 
covered in places with hard, woody processes in the form of broad cones up 
to 2.5 mm. high and often with crater-like depressions. Such processes, just 



1 Berichte der Generalversammlung des Vereins zur Forderung- der Moorkultur 
Jahrg. 1895, p. 123. 

2 Elfter Jahresiber. d. Sonderausschusses f. Pflanzenschutz. Arb. d. Deutsch. 
Landw. Ges. Part 71, p. 130. 

3 Hollrung-, Die verschiedenen Bodenarten und ihre Eig-nung fiir den Riibenbau. 
Blatter f. Zuckerrubenbau, 1905, No. 14, p. 217. 



259 

like the tissue cushions on the various deciduous bark layers, which are like 
warts and occur in lines, were found always on the inner side of the layer 
which was being raised up and had exactly the appearance pictured later 
under the section "Bark Refuse" in the elm. This section should be con- 
sulted. 

The greatest possibility of separation of the lamellae from one another 
was found where a rotted tissue layer, i. e., in a condition of humifaction, be- 
gan to disintegrate and formed a surface of separation. The rotted bark con- 
sisted of cork cells, as shown on the upper side B in the accompanying cross- 
section (Fig. 35), while H shows the bark which lay nearer the wood, and 



rp' 



Fig. 35. Mouldy bark scale of a pine from the Liineburg-er moor. (Orig-.) 

therefore was younger; rp is corked^ firm bark parenchyma while k is the 
full cork, loose bark parenchyma and t the plate cork. The bark scales were 
therefore composed of bark parenchyma elements, which advance further 
and further toward the fresh bark and the cambium. They are separated by 
layers of sheet cork and become suberized. Besides this, we also find clus- 
ters of loose cells, which are more abundant the deeper the base of the trunk 
has stood in the moss. The spongy constitution of the underside of the dif- 
ferent bark lamellae arises from the morbid luxuriousness of the parenchyma 
and full-cork masses. As a result of the moisture and the scanty supply of 
oxygen, these excrescence tissues become slimy and form the rotted bark, 
which facilitates the separation of the lamellae. 



26o 

The great part which the bark parenchyma, with its abnormal phenom- 
ena of stretching, plays in the formation of the bark shows that this de- 
velopment of rotten bark in the moor pine is related to the "hark refuse" of 
the elm and distinguishes both cases from the actual tan disease (see page 
215) in which the formation of full cork has the upper hand, as in the many- 
layered lenticels. 

Horticultural Moor Plants. 

The growers, probably because of their study of the natural habitat of 
our heather plants, have used for imported Ericaceae the soil in which our 
Calluna grows splendidly: — i. e., heath moor. The properties of Sphagnum 
peat, thus ascertained, have made this a desired article in trade. Its ad- 
vantages consist in its loosening properties. The results of experiments in 
cultivating Ericaceae led to the mixing of the so-called moor soil with 
heavier nutritious soils as a loosening substance. In this way, the moor soil 
has been introduced as a necessary element in soil mixtures for most of the 
hner horticultural plants. Since no standard was known, however, for a 
good moor soil, many kinds came into trade, with the growing demand. Some 
were either over rich in raw humus, or resembled the character of the 
meadow moor. The dark color of the meadow moor led to the incorrect 
opinion that a very nutritive earth was present. The results of this mis- 
conception were very evident. The complaints of gardeners about acid heath 
soils are almost universal and the degeneration of many favorite plants, such 
as the so-called new Holland, or "Cape plants," could not be arrested. 

Where meadow moor was used as an admixture in soils for potted 
plants, its properties quickly manifested themselves. In a dry condition, 
this moor soil seems to be easily pulverized, decomposing into a powder, or 
remaining crusty. When wet, however, it becomes smeary and cements the 
other particles of soil into dense masses with a poor air content. Since 
meadow moor heats greatly, the upper layers in the flower pot dry out easily, 
become lighter colored and suggest to the gardener that the whole ball 
of soil is dry and should be watered. Here is the danger, for meadow moor 
deceives as does no other soil. If such moors be investigated in nature, the 
smeary condition is found directly under the dusty surface, a few centi- 
metres deep, since the very binding substance retains the water unusually 
long. Potted plants are often killed by a lack of oxygen at the roots, even 
if the humic acids are not taken into consideration. These, however, play a 
disasterous role and often cause the injury arising in many cases from the 
use of loose, fibrous marsh soil. Sphagnum peat is the most beneficial be- 
cause the leaf is so constructed that it makes a very porous soil, giving rapid 
moistening and as rapid an aeration of the soil in the pot. The excellent re- 
sults obtained in growing orchids with sphagnum are well known. Good re- 
sults will only be had with fibrous moor soils, full of fragments of Vaccin- 
ium and other moor plants and taken from forest soils, if the raw humus is 



26l 

removed and the decomposed layers used ; even an admixture of lime, or still 
better, of calcium phosphate is advisable. 

I have mentioned the poor growth of plants in moor earth in a special 
section, because I am of the opinion that a very considerable number of phe- 
nomena of disease may be traced to the acids in the soil, — the gardener says 
that the soil smells sour. Even those specific plants, such as Rhododendron, 
Azalea, etc., only thrive when, as in their natural habitat, they stand in 
fibrous earth which is easily aerated. In the moment when a mixture of 
moor soil with more nutritive solid soils is used for potted plants, we find 
root-decay, which is indicated by the brown edges of the leaves. I consider 
the theor}^ of the necessity of an admixture of moor soil in cultivating the 
majority of our finer potted plants to be erroneous. As far as my experience 
goes, sand can give incomparably better results as a loosening material. The 
gardener should work with well decomposed leaf mould or compost earths 
and add large amounts of sand. If care also is taken to have good pot 
drainage, there will not be so many complaints about root diseases in the 
future. 

Specking of Orchids. 

A special illustration of the advantages of the use of sphagnum, de- 
scribed in the previous division, is found in the peculiar black spotted con- 
dition of the leaves of epiphytic orchids. In our green houses there are 
many leaf diseases which frequently arise from fungus infection (Gloeo- 
sporium and CoUetotrichum, Phoma, Phyllosticta, etc.). We find many cases 
however, in which fungi take no part or occur only secondarily and among 
these an infection should be emphasized especially which may be found in 
Cattleya, Laelia, Dendrobium and the members of the group of the Vandeae. 

The course of the disease is explained best by the description of a special 
case, which, occurring in Phalaenopsis amahilis var. Rimenstadiana^ , has re- 
cently been studied more closely. All except the youngest leaves of plants 
grown in leaf mould in pierced pots and watered with tap water were 
spotted yellow to black. The disease advanced apparently from the older to 
the younger leaves and manifested itself, in its early stages, by the appearance 
of irregularly round or oval, pale, translucent spots. These were scattered 
over the whole leaf, but usually appeared first and most abundantly at the 
tip. When such leaves were cut off and lost water by evaporation, the spots 
which became pale at the beginning of the attack,, could be felt like warts 
over the healthy leaf. These conditions changed, however, as the disease ad- 
vanced, since the yellow spots at once took on a whitish appearance and 
were depressed like saucers. In' this it was seen that different adjacent cen- 
tres of disease coalesced, forming connected, thin surfaces, which finally 
turned a deep blackish brown and were enclosed like a wall by the healthy 
tissue. After turning brown, however, the spots did not increase in size 



1 Sorauer, Erkrankung von Phalaenopsis amabilis. Zeitsohr. f. Pflanzenkrankh., 
1904, Part V. 



262 

There were also centres of disease, which remained restricted to definite 
groups of tissues. 

When one of the browned spots, covered with longitudinal bands due to 
ihe darker veining, was cut through, it was found that its paper-like consis- 
tency was not produced by a possible atrophy of the tissues, resulting from 
an injury due to insects, or from bacteriosis, but only by the drying 
together of the mesophyll cells, which have been almost entirely depleted of 
iheir contents. The boundary between the dead and the wall-like convex 
bordering healthy tissue was sharp, with no transitions. The collapsed brown 
or (mostly) light walled tissue when treated with iodine, showed only iso- 
lated flakes of cytoplasmic contents together with little drops of a colorless 
or golden-yellow substance. With the entrance of water, the cell walls, like 
the folds of an accordion, were raised somewhat from one another, without 
the cells having been brought to their previous size. In the absolutely dead 
tissue isolated, colorless, slender mycelial threads were found at times. 

If glycerine was allowed to act on the fresh sections, which, moreover, 
also gives a strong acid reaction at the diseased spots and shows no oxydases 
and peroxydases with guaiak and hydrogen peroxid, large, irregular or 
usually spherical masses were drawn together in the cell contents. This phe- 
nomenon was often found in especially sappy tissue, rich in sugar. At the 
periphery of these masses lay the chloroplasts. In the badly diseased parts 
these groups of substances could not be found at all, but only numerous very 
small or somewhat larger drops. Just as little can this contraction of the 
cell contents into strongly refractive drops be proved in the healthy part of 
the leaf. We might place it in the list of glucoses because, with the Trom- 
mer test, they show in places precipitates of cuprous oxid. 

Further anatomical investigations led to the discovery that, in the var- 
ious yellowish tissue centres, the cell content was used up too strongly, and 
the mesophyll cells had grown out wider. The diseased place thus became 
somewhat swollen up over the healthy surface, but at once the diseased tissue, 
which had lived out its life very rapidly, showed this by the appearance of 
carotin drops ; it collapsed, turned brown, and dried up. This process of 
drying, however, is limited, in all cases observed as yet, to the leaf region 
characterized in the beginning by the turning yellow. In this the phenome- 
non is distinguished from fungous infections. Since now enormously in- 
creased formation of sugar can be proved and the absence of parasites de- 
termined in the majority of spots, we have under consideration a constitu- 
tional disease which set in, where the orchids named were cultivated in leaf 
■mould. 

This cultural method has been especially recommended in the last few 
years by Belgian and EngHsh gardeners and introduced into Germany in 
part with the use of Flemish leaf mould. After the rapid spread of the dis- 
ease, the old process of growing the plants in a mixture of sphagnum with 
bits of moor soil was again followed and the eariier results were again ob- 



263 

talned. From this it is evident that leaf mould, an extremely favorable sub- 
stratum for most other plants and in which the orchids named at first grow 
very well, gradually becomes slimy when copiously watered (especially with 
water containing algae) and does not let the necessary supply of oxygen 
reach the roots of the orchids. 

Much better results have been obtained with the so-called Jadoo fibre, 
a very porous moss peat saturated with nutritive salts. Yet the result does 
not justify the increased expense and the old sphagnum culture always 
proves to be the most advantageous. The modern endeavor of growers to 
force the orchids to an earlier and more luxuriant development by abundant- 
ly supplying nutritive substances, high temperatures and great moisture, 
gives actual good results only for a limited time. Usually a reaction sets in 
in the over-stimulated plants, which can be prevented only by a dormant 
period in a relatively cooler, drier place. 

Cooler, drier sand is also in many cases the best protection against decay 
from fungus. Klitzing observed a very instructive example in a spot dis- 
ease of Vanda coerulea, called forth by Gloeosporium which is now pretty 
universal on the continent and in England, as well as even in our country. The 
statements of the collectors show that this Vanda is found in the Himalayas 
on Gordonia, which grows in moderately warm, windy habitats. Here, in 
(lur conservatories, the plants are cultivated, on an average, more than io°C. 
warmer and kept year in and year out in closed, moist greenhouse air. Nat- 
urally the plants become more tender on this account and succumb within a 
few days when artificially infected with Gloeosporium, while, in their native 
habitat, the fungus is restricted and the plants develop further and increase, 
despite its presence. 



CHAPTER III. 



UNFAVORABLE CHEMICAL SOIL CONSTITUTION. 



I. Relation of the Food Stuffs to the Soil Structure. 



A. Soil Absorption Resulting from Chemico-physical Processes. 

Injuries to vegetation can take place either because the capital of nu- 
tritive substances in the soil takes a form quantitatively or qualitatively un- 
favorable for the nutrition of the plants, or because, with an abundant sup- 
ply and normal composition of the nutritive substances, the plant's capacity 
for taking them up will be arrested by other factors of growth. Thus, either 
a lack or an excess of the nutritive substances can make itself felt, or, be- 
cause of modified conditions of absorption, one single nutritive substance 
can be present in amounts too scanty or too great for effectiveness, and thus 
disturb the equilibrium in the organism. This second form of nutritive 
disturbance will be treated in the following division under the headings, 
"Lack of moisture and nutritive substances" and "Excess of moisture and 
nutritive substances." 

The consideration of the supply of water in this connection, together 
with nutritive substances, is justified by the fact that the water not only 
furnishes these by its decomposition in the plant body, but also, as 
a transporting medium, causes weak or strong concentrations of the 
nutrient solutions according to the amount of water present, thus influencing 
beneficially or disadvantageously the process of nutrition. In view of the 
constantly changing concentrations, the influence of the water vvill therefore 
have to be taken into consideration, when studying the relation of the nutri- 
tive substances to the soil structure. 

The soluble salts produced by the decomposition of the minerals or in- 
troduced by fertilization, serve as a basis for soil absorption. The retention 
and giving up of the salts, as also their transformations continually taking 
place in the soil, were thought at first to be predominantly physical processes, 
while they now, in substance, are considered chemical processes^ In any 

1 See Ramann, Bodenkunde, 2nd. Edition, p. 21, Berlin, 1905, Jul. Springer. In the 
remainder of this section, if other authors are not cited, we rely chiefly on the work 
here named. 



265 

case, it is difficult to draw a line between physical combination (absorption) 
and chemical combination. 

Absorption becomes of importance, only where large absorptive sur- 
faces are offered, as in organic substances and certain inorganic ones, to 
which belong the colloidal siUcic acid and the colloidal ferric oxid of the 
tropical red soils. Those humus substances, capable of being swollen, seem 
of the greatest significance which are precipitated in soils rich in nutritive 
substances, such as salt-like compounds, but remain to a great part in solution 
in impoverished soils. In the absorption of humus substances the first role is 
played by their capacity to take up free bases and their carbonates. The 
acid humus substances are especially effective for the ammonia found in the 
soil and for ammonium carbonate and we take advantage of this fact 
especially when using a peat mulch. 

Besides colloidal substances, the finely distributed mineral elements 
should be kept in view as a means of absorption. Of the minerals, how- 
ever, quartz always and kaolin, when not combined with alkali silicates to 
form the absorptive double silicate, have no capacity for absorption. The 
chief bearers are the hydrated silicates, especially the double silicates of 
aluminum, which, crystallized as zolites, are found in rocks, and also those 
of ferric oxid. They make possible the exchange of bases observable in the 
soil. 

This becomes effective with the exhaustion of the soluble nutritive sub- 
stances in the soil as is made clear by the following experiment carried out 
by Lomberg\ A hydrated silicate was kept for three weeks in contact with 
water containing carbon dioxid, and, after some time, the following compo- 
sition was found : — 

I. II. 

Original silicate. After treatment with water 

containing carbon dioxid. 

Silicic acid 46.64 per cent. 54-03 per cent. 

Aluminum oxid 29.38 " " 39-65 " " 

Potassium 22.75 " " 5-34 " '* 

Sodium 1.83 " " 0.00 " " 

If this leached silicate II. was again treated with a solution of caustic 
potash, the following composition was found, — silicic acid, 46.60 per cent. ; 
aluminum oxid, 35.67 per cent. ; potassium, 17.73 P^r cent. Therefore, in the 
silicate skelton, the greatest part of the potassium had been taken up again, 
so that a new condition of chemical equilibrium had been set up. 

If ammonium chloride was added to the original silicate I, the reaction 
resulted in, — silicic acid, 56.17 per cent.; aluminum oxid, 34.59 per cent. ; 
potassium, 0.89 per cent.; ammonia (NH3) 8.37 per cent. If a very large 
excess of calcium salts had been present, instead of the ammonia, the cal- 
cium could have replaced the potassium entirely in the silicate, as has act- 

1 Zeitschr. d. Geol. Ges. 1876, p. 318.. 



266 

ually been shown by Riimpler's experiments and later those of Schloszing 
Such processes are constantly present and show how quickly a soil can be 
leached by continued abundant precipitation, or can be impoverished in the 
supply of its other valuable food stuffs by a one-sided supply of fertilizer. 

The addition of fertilizer and the consequent increase of nutriment does 
not always give the expected increase in the yield. This occurs especially in 
rich soils and is explained by the fact that such a soil is no longer in a con- 
dition to absorb, as a direct result of its wealth of nutriment. Soils poor in 
clay are especially able to cause such phenomena because of their small ab- 
sorptive power. 

A further painful surprise, connected with absorption, is the poisoning 
of the soil from metallic salts. All heavy metals combine actively and, on 
this account, for example, the failure of crops, observable near smelting 
works, may not always be ascribed to the sulfuric acid of the fuel alone, but 
often also to the larger accumulations of metallic compounds. The fact, as 
shown by experience, that plants will live in soil containing small quantities 
of copper, lead, zinc, etc., has, up to the present, prevented paying the neces- 
sary attention to this kind of soil poisoning. 

With potassium and ammonium, both of which combine actively, ab- 
sorption often takes place by exchange in equivalent amounts (3 parts K2O 
for I part NH3), whereby sodium, calcium and magnesia pass over into 
solution. The easily dissolved, salt-forming sodium is only weakly absorbed 
and, to a still lesser degree, the calcium, present in the form of its humate, 
carbonate or phosphate, which can easily be replaced in the silicates by other 
bases. Magnesium acts similarly. Acids are combined only when they form 
insoluble salts. This is especially the case with phosphoric acid, which 
forms insoluble compounds with calcium, magnesium, ferruginous earth and 
aluminum oxid. Sulfuric acid is very weakly absorbed, nitric acid and 
chlorin not at all. The latter case deserves consideration in the chlorin 
poisoning near hydrochloric acid factories. 

By the different absorptive capacity and the constant exchange of nu- 
tritive substances is explained the effect of many fertilisers which have a 
two-fold action,- — disintegrating and thereby increasing nutriment and ex- 
hausting the supplies. Thus an abundant supply of potassium salts and 
Chili saltpetre exhausts the calcium and magnesium in the soils. The ex- 
pression, "soil impoverished from marling" indicates that marl, as well as 
gypsum, can prematurely exhaust the nutritive stores in the soil by a disin- 
tegrating action. In this disintegration lies also the value of sodium chlorid 
(common salt). A greater source of poor production is found in the acid 
content, especially in the abundance of humic acids which greatly weaken 
the absorption and are in a condition to dissolve all the elements in the soil. 
This subject has been treated more thoroughly under the disadvantages of 
moor soils and under the formation of swamp ore. 



267 

The less the various nutritive substances are retained and the more 
soluble their compounds, the more easily they are leached out. At best, they 
reach the deeper soil layers, and in regions of strong sudden precipitation, 
rhey can be carried away. The chlorids present in small amounts in most 
soils are most easily removed, then the nitrates, later the sulfates. This 
takes place slowly with carbonates of calcium and magnesia and the phos- 
phates are the most persistent of all. Chlorids are dangerous for agricuUure 
in regions of very slight precipitation, where they accumulate in low lying 
places, and produce highly concentrated soil solutions. Under the same con- 
ditions, the so-called "alkali soils" are produced by carbonates and sulfates. 

The question of nitrogen is the most important. The nitrates are so 
very soluble that the upper soil layers, containing the superficial roots, can be 
leached of all their nitrates even if the subsoil contains abundant nitrogen. 
This can only be made available by means of deeply rooted plants. In the 
face of general practice, not enough emphasis can be laid on the great losses 
occurring with unsuitable fertilization of the fields. Of the calcium sahs, 
gypsum must be considered since it contains sulfuric acid. With calcium 
carbonates in damp climates, even on soils made from disintegrated lime 
stone, the calcium content may be poor because the carbonate is slowly 
leached out^. On the other hand, all the potassium phosphates as well as 
the phosphoric compounds (with the exception of the alkalis) belong among 
the most persistent minerals. An exception takes place only in soils with 
free humic acids. Here the phosphates and also the iron compounds be- 
come soluble and even the resistant silicates are decomposed and carried over 
in a soluble form. In this way moor soils are exhausted of all their mineral 
elements, excepting quartz. 

The natural process of enrichment of the soil by weathering and by the 
action of wind in moving soil masses, by the decay of organic substances, 
etc., which effectively counteract leaching, is of value only in long-lived 
plantations. Here the fact, that the deep growing roots get the nutritive sub- 
stances from the subsoil, again made available for the upper soil layers by the 
falling of the leaves, is surely of great importance. In our plantations of 
one and two-year old plants, we find this help only in the use of green 
manuring. 

Finally, soil impoverishment from draining must not be passed over. 
However useful this practice is, as already acknowledged under soil aeration, 
in places it can act most injuriously. This refers especially to the leaching 
of nitrates from the soil in localities, where the fertilizer cannot be exten- 
sively supplied. Naturally the loss reaches a significant amount where an 
abundant supply of nitrogen is present, as is shown, for example, in Levy's 
analyses of the drain water from tlie Parisian sewage fields-. In a liter of 



1 (If water containing- carbon dioxid comes in contact with calcium carbonate 
it forms calcium bicarbonate, which is much more soluble and passes off in the 
drainage waters. This always occurs in soils containing- organic matter. — H. S. R.) 

- Wollny, E., Die Zersetzung der organischen Stoffe, etc. Heidelberg 1897, p. 4. 



268 

the drainage liquid, as it flowed away, were contained 0.8 to 0.9 mg. of nitro- 
gen in the form of ammonia and between 19. i to 27.1 mg. of nitrogen in the 
form of saltpetre. The liquid sewage used for the irrigation contained 24.9 
mg. ammonia nitrogen and 0.9 mg. saltpetre. A comparison of these figures 
shows that the fertilizing nitrogen introduced in the form of ammonia is 
oxidized almost entirely to nitric acid by. bacterial action during its filtering 
through the soil. Way's investigations^ show that, on an average, no very 
large amounts of mineral elements may be detected in drain water. He 
found in 1000 parts only 0.003 parts of potassium, 0.186 of calcium, 0.138 
of sulfuric acid, 0.002 of phosphoric acid, etc. Nevertheless we should not 
forget that continued reductions are involved which are added to one an- 
other, in case there is abundant drainage. 

A comprehensive summary of lysimeter experiments in Rothamsted, 
which covered 35 years, and more recent investigations in Holland- show 
how rapidly, as a rule, the nitrification of the fertilizers, such as the ammonia 
salts, takes. place of itself. Even in the fall and winter the nitrification is so 
active, that great nitrogen losses may be expected. On this account it is ad- 
visable to use ammonia salts as a top fertilizing in the spring. 

When using sulfates and chlorids of ammonia, the calcium combined 
with the sulfuric and hydrochloric acids is washed away in large quantities 
in the drain water. This process is necessarily preliminary to the combi- 
nation of the ammonia in the soil and the subsequent nitrification. H the 
calcium carbonate does not suffice for this conversion, the ammonia salts 
easily become dangerous for the plants. Since the sulfates and chlorids of 
potassium, like those of ammonium, form gypsum and calcium chlorid, which 
are not absorbed by the soil, the necessity of a periodic liming is evident. 

B. The Work of the Soil Organisms. 

The activity of animal life in relation to the changes in the soil is men- 
tioned in the third volume of this work. In this is concerned primarily the 
work of the soil bacteria, the agricultural significance of which has been 
shown in a Very comprehensive short summary by Behrens^ and Hiltner*. 

According to the chief work performed by the bacteria, we could speak 
of those which set free the nitrogen and others which attack the carbon 
compounds (as, for example, the pectin and cellulose ferments) and finally 
those forming humus and those decomposing it. But not only the action of 
these organisms on their substratum is of importance here, but, especially, 
their influence on each other. Some genera or species disintegrate one an- 
other, others nourish each other. 



1 Further analyses by A. Mayer, Agrikulturchemie. 5th. Edition, 1902, Vol. 2, 
Section I, p. 118. 

2 Beleuchtung der Bodennitrifikation durch Drainwasseruntersuchungen. Mit- 
teil. d. D. Landw. Ges. 1906, Stiick 13. 

3 Behrens, Die durch Bakterien hervorgerufenen Vorgange im Boden und Dun- 
ger. Arb. d. Deutsch. Landwirtsch.-Ges. 1901, Part 64. 

4 Hiltner, L,., Ueber neuere Erfahrungen und Probleme auf dem Gebiete der 
Bodenbakteriologie etc. Arb. d. Deutsch. Landwirtsch.-Ges. 1904, Part 98. 



269 

The influence of carbon disulfid serves as an important example, for, 
besides a poisonous action, a stimulus directly beneficial to growth has been 
assumed for it. The latter is thought to be recognized in the fact that a 
clearly recognizable increase of fertility sets in after the disappearance of 
the carbon disulfid and its influences which arrest growth. Hiltner suc- 
ceeded in proving that the carbon disulfid chiefly conditions the changing 
phenomenon by disturbing the equilibrium of the bacterial flora of the soils. 
By means of its ability for dissolving fats, it suddenly forces back the bac- 
teria which had prevailed up to that time, just as it also stops entirely the 
increase of all species, so long as it is present unchanged in the soil. If the 
poison become diluted, or disappears through conversion, the long repressed 
numerical growth of the soil organisms increases in such a way, that, for 
example, an increase of 9 millions of the species growing on meat-pepton- 
gelatine to 50 millions in one gram of soil could be proved in one case. Thus 
an increase in the nitrogen production and with it of the potato harvest 
could be determined chemically by Moritz and Scherpe. 

With reference to the behavior of the nitrogen bacteria described in the 
second volume^ under soil bacteria, we will here only supplement 
the facts stated there. After Winogradski especially had proved the con- 
version of the ammoniacal nitrogen to nitric nitrogen to be the successive 
achievements of two different groups of bacteria (builders of nitrites and 
nitrates), it was determined by Omeliansky that the nitrogen of the organic 
substances must have been previously converted by other bacteria to am- 
monia. Disturbances can easily occur in this work, since these bacteria are 
most sensitive to dissolved substances. Thus, for example, the activity of 
the organism forming nitric acid stops absolutely if any traces of ammonia 
are present. 

In contrast to the above, numerous other species of bacteria (more than 
twenty have already been identified) possess the ability of denitrification, i. e.; 
the reduction of the saltpetre to free nitrogen which passes off into the air. 
People have wanted to trace to this process the fact that fresh stable manure, 
under certain circumstances, injures the saltpetre contained in the soil and 
that strazv fertilizing acts disadvantageously. This phenomenon is now 
chiefly explained by the fact that protein forming organisms have laid hold 
of the available nitrogen in the soil. (Pfeiffer and Lemmermann as well as 
Gerlach and Vogel). These bacteria transform the saltpetre first into the 
nitrite and then into protein-like compounds. That definite secondary con- 
ditions belong here is shown by Hiltner's experiment in which straw fertiliz- 
ing was proved to be very injurious for potted plants, while the same 
amounts on open land had a beneficial effect. This contradiction may prob- 
ably be traced to the fact that the protein thus produced can be transformed 
more quickly in open ground to products which can be utilized again. 



1 (Page 89 in the German edition.) 



2/0 

In studying the conversion of nutritive substances and their transfor- 
mation by soil bacteria, the process of the storage of nitrogen, i. e., the assim- 
ilation of free nitrogen by bacteria, is to be considered. Besides the anaerobic 
Clostridium Pastorianum (Pasteurianum), determined some time ago by 
Winogradski, which with sufficient amounts of carbo-hydrates can make 
use of the atmospheric nitrogen for its nutrition, — aerobic species have been 
found by Beijerinck such as Asotohacter chroococcum. This species, present 
in every field soil, consumes extremely large amounts of carbo-hydrates by its 
nitrogen assimilation (according to Gerlach and Vogel 8.9 mg. nitrogen in 
I gram grape sugar). 

The changes in forest litter should be included here. The nitrogen en- 
richment due to them has been caluculated by Henry^. He emphasizes that 
nitrogen is stored up with the decomposition of dead oak and beech 
leaves and spruce needles. This decomposition is very active on damp soil in 
summer, but scarcely noticeable in winter, or when mixed with soil. Ac- 
cording to his calculations, fallen oak leaves accumulate 20 kg. of nitrogen 
per hectare within a year. On dry soil the dead foliage either does not be- 
come enriched at all (in the red beech), or only very insignificantly (white 
beech, spruce). In no case, however, was any loss of nitrogen noticed. 

The active enrichment of the soil by the symbiotic tubercle-forming 
bacteria should also be mentioned here. Cultures of these bacteria have been 
introduced into commerce under the name "Nitragin"- and cultures of non- 
symbiotic nitrogen gatherers are sold under the name "Alinit.'* More recent 
investigations indicate that not only bacteria of the same species adapted to 
individual host plants may be assumed, but that even different species may 
be distinguished. Hiltner contrasts two species chiefly on account of their 
morphological and physiological differences ; viz., Rhizobium radicicola and 
Rh. Beijerinckii. The activity of these tubercle bacteria in their relation to the 
Leguminoseae begins only when the Leguminoseae have suffered for some- 
lime from nitrogen hunger and they are inactive when nitrates are present in 
the soil. This should be mentioned only in passing to illustrate further the 
dependence of bacterial life on various factors. The root secretion of each 
plant must also count as such a factor. Even the very healthy seeds which 
get into the soil and the green parts of healthy seedlings have a specific bac- 
terial flora, which can increase greatly and swarm out into the soil. Other 
micro-organisms can be pressed back by these^. From such inequalities of 
the growth conditions in the soil must arise necessarily significant fluctua- 
tions in the individual number of each species of bacteria and thereby in the 
whole achievement so far as the production of nutriment favorable for culti- 



1 Henry, E., Ueber die Zersetzung- der abgefallenen Blatter im Walde etc. (Annal. 
Sc. Ag-ron. franc. VIII). cit. Centralbl. Agrik. Chem. 1904, p. 793. 

2 In regard to soil inoculation, it should be taken into consideration that bac- 
teria, like all plants, will thrive only when the soil is so constituted that it favors 
their increase. As Remy has very characteristically expressed it, "they must find 
theip proper soil climate." 

3 Dliggeli, M., Die Bakterienflora gesunder Samen etc. Centralbl. f. Bakt. II. 
1904, Vol. XIII, p. 198. 



271 

vated plants is concerned. If now, for various reasons, as, for example, 
specific root secretions, certain species of bacteria, which are attracted to 
any definite plant variety and incited to great increase, carry over various 
nutritive substances, primarily, nitrogen, in a form unfavorable for the culti- 
vated plants, it can happen that chemically the supply of nutritive substances 
may be sufficient, perhaps even abundant, and yet the product may fall off. 
We then face the phenomena of soil exhaustion or "fatigue." Hiltner men- 
tions experiments in reference to this. He perceived definite indications of 
soil exhaustion in the third generation of peas, which during a period of 
three years were grown seven times in pots in the same soil, but differently 
fertilized. "The plants became sick, were easily susceptible to attack, turned 
yellow prematurely and gave poor seeds." In the later generations, the dis- 
eased conditions were overcome in this experiment. "The roots of the pea 
plants were now noticeably browned, but were perfectly white and healthy 
inside, and it could be proved that a regular bacteriorhiza was present, which, 
formed by well-adjusted, beneficial bacteria, prevented the further penetra- 
tion of the injurious organisms."^ 

In regard to the exhaustion of the grape, Behrens (loc. cit., p. no) cites 
the observations of A. Koch, according to which it could be produced by an 
accumulation of injurious micro-organisms. After sterilizing the diseased 
soil (not the healthy soil), the growth of the vines improved. 

If such a change in the composition of the bacterial flora takes place in 
a direction injurious to cultivation, it explains the increase of soil exhaustion 
due to the repeated growth of the same plant on any given piece of land, 
with short intermissions. And this accumulation of destructive elements is 
of importance not only for the bacteria, but also for other vegetable and 
animal enemies which can cause soil exhaustion. 

Among the bacteria which accumulate in the soil with repeated culti- 
vation of the Leguminoseae, Hiltner found that the pectin fermenting organ- 
isms became active. He found that in soil greatly exhausted by peas, per- 
fectly healthy pea seed rotted especially because of these bacteria known as 
acid formers. 

Another variation in the normal work of soil bacteria is the turning the 
fertilizer to peat. In heavy soils, often after some years, the fertilizer has 
been found pretty much undecomposed. In the same way green manure 
turned under too deep, turns to peat. As a result of the limited supply of 
air, the formation of raw humus is completed. The end and aim of working 
the soil, however, is the production of a suitable himius covering, for by 
the humus we obtain an equalization of the extremes of heat and cold, mois- 
ture and drought and the suitable nutritive soil which alone makes the exis- 
tence of most bacteria possible. If this is present, field soil can develop its 
actual life, which, to a certain degree, is measurable by the production of car- 
bon dioxid. How the bacteria co-operate in this, is shown by some statements 



1 Bodenpflege und Pflanzenbau. Arb. d. D. Landwirtsch.-Ges. Part 98, p. 74. 



2^2 

of Stoklasa and Ernst^, who reckoned the respiratory intensity from loo g. of 
dry substance of the Bacterium Hartlehi, a denitrifying bacterium, to be 2.5 
g. of carbon dioxid per hour; in the same amount of dry substance of Clost- 
ridium gelatinosum, an ammonia former, the ouhure gave 2.0 g. carbon 
dioxid. The fact that the carbon dioxid production of a held is actually de- 
pendent primarily, on bacterial life, is demonstrated by the circumstance that 
no carbon dioxid was produced in observ^able quantities after experimental 
earth had been sterilized. 

We find the following statements in the work of the above named 
authors on the influence of aeration. Forest soil taken from a deep position 
gavei 59 mg. per kilo, of carbon dioxid within 24 hours in aerobiosis o mg. 
in anaerobiosis, while peat soil yielded 41 mg. in aerobiosis and 7 mg. in 
anaerobiosis. Naturally, heat and moisture also act determinatively. The 
greater the production of carbon dioxid in a field, the more completely does 
the chemical process of the combination of the free ammonia take place, as 
Schneidewind- has observed. This question comes under consideration here 
in as much as the losses in nitrogen with an addition of animal manure rep- 
resent an impoverishment of the stores in the soil. If stable manure with 
ordinary treatment is left in a manure pit, it shows a nitrogen loss of 30.31 
per cent, after lying three months. If it lies, however, on an underlayer of 
old manure, producing a great deal of carbon dioxid, the loss amounts only 
to 16.94 per cent. Here the abundant carbon dioxid must have combined the 
free ammonia or have prevented the disassociation of the ammonium carbo- 
nate already formed. 

Among the most serious injuries, because the most frequent, be- 
longs the so-called "unripe soil." This is distinguished by its lack 
of elasticity from the ripe soil which, under the influence of the soluble 
salts in the soil and the micro-organisms, takes on the friable structure al- 
ready described. In consideration of the great work which the bacteria per- 
form in soil decomposition, we can assert that the ripeness of the soil is due 
to their work. If we do not know by far all the processes taking place in 
ripening soil, we do know that we may consider the ripening up to a certain 
stage as actual fermentation. Attention need be called here only to the special 
pectin fermenting organisms (Plectridia) which seem of importance in germ- 
inating seeds of the Leguminoseae and further to the cellulose fermenting 
organisms with the great formation of hydrogen and methane (marsh gas 
CH4). Further, the Streptothrix species come under consideration as humus 
fermenting organisms, but especially the granulose organisms forming acids^, 
which produce chiefly butyric acid and carbon dioxid. In this, the Plectri- 
dia take over the chief share in the mineralization of the organic substances. 



1 Stoklasa, J., and Ernst, A., Ueber den Ursprung-, die Menge und die Bedeutung 
dee Kohlendioxyds im Boden. Centralbl., fiir Bakteriologie etc. Section II,' 1905, Vol. 
XIV, Nos. 22 and 23, p; 725. 

- Schneidewind, Zur Frage der Stalldiingerkonservierung. Deutsche landw. 
Presse 1904, No. 73. 

3 Lohnis, F., Ueber die Zersetzung des Kalkstickstoffs. Centralbl. f. Bakt. II, 1905, 
No. 3-4, p. 87. 



273 

The nitrogen collectors (Bacillus radicicola and B. niegateriuni, Clostridium 
Pasteurianum, Azotobacter) as also the ones forming ammonia {Bacillus 
ureae, B. albuminis, B. proteus vulgaris'^, B. butyricus, B. mycoides, B. siib- 
filis, B. mesentericus vulgatus, B. foetidus, Bacterium coprophilum, etc.) the 
nitrifying Bacterium nitrobacter, etc., and the denitrifying genera 
{Bacillus mycoides, B. substilis, B. liquidus, B. nubilus, B. vulgaris, B. 
coli, B. prodigiosus, B. liquefaciens. Bacterium fuscum, Closteridium gel- 
atinosa, etc.), have been considered and attention should now be called to the 
specific organisms of decomposition. All these biological processes are 
enacted in ripe soils, supplementing or combatting one another, according to 
the climatic conditions of the soil at the time. 

Besides bacteria, green algae, the appearance of which counts as a sign 
of good ripening, have been considered to be nitrogen collectors. According 
to Koch", however, this is not the case, but their value lies in the fact that 
by their chlorophyll activity they furnish carbon for the soil bacteria, which 
combine nitrogen. Beijerinck, Sch losing and Laurent insist that the blue- 
green algae can assimilate free nitrogen and, according to Saida^^, a number 
of mold fungi should also have this ability. 

As Treboux* has recently emphasized, the activity of the nitrite and 
nitrate bacteria may frequently be lost, but the ammonia retained in the soil 
is always at the disposal of the plants and used up by them; this may still be 
taken for granted for many cases. Other investigators have also proved the 
usefulness of ammonia. Ultimately, however, the formation of the ammonia 
in the soil is based on the decomposition in which bacteria participate. 

The growth of the majority of micro-organisms affecting the fertilitv 
of the soil is connected with an abundant fluctuation in moisture, and the 
passage of heated air over the soil with its drying effect. These conditions 
are lacking in heavy soils in wet periods, — i. e., the soil remains unripe. 
Here the cultivation of useful soil bacteria succeeds only with a constant 
working of the soil. Acknowledged practical workers recommend the 
quickest possible turning over of the grain stubble on loamy soils in order 
to obtain a greater nitrogen gain by an earlier soil ripening. In the Lauch- 
stadt experiment station about the same results were obtained by early 
ploughing as by a green manuring. In spring planting on all heavy soils, a 
fall ploughing is the best precaution against unripe soils. 

Recently, letting the ground lie fallow-' has again come into use for 
heavy soils. In light soils it should be considered a wasteful process. The 
benefit of letting ground lie fallow is its disintegrating action; no final de- 

1 Stoklasa, J., Ueber die Schicksale des Chilisalpeters im Boden etc. Blatter f. 
Zuckerriibenbau 1904, No. 21. 

~ Koch, A., Bodenbakterlen- und Stickstofffrage. Verb. d. Gesellsch. deutcher 
Natur. zu Kerlsbad. 1903. Part I, p. 182. 

3 Vog-el, J., Die Assimilation des freien elementaren Stickstoffs durch Mikro- 
crganismen: Centralbl. f. Bakteriol. II, 1905. Vol. XV, p. 174. 

* Treboux, O., Zur Stickstoffernahrung der griinen Pflanzen. Ber. d. botan. 
Gesellsch. 1905. p. 570. 

5 Hillmann, Bedeutung der Agrikulturphysik etc. Nachrichten aus dem Klub 
der Landwirte, 1902, No. 453 and Mitteil d. D. Landw.-Ges. 



274 

cision has been reached as yet as to how this effect is produced. It is thought 
that in this, physical, chemical and soil bacteriological processes interact 
supplementarily. The frequent thawing and freezing in the winter serves 
to break and loosen the soil. Thus the action of the atmospheric processes 
is favored and the soil opened for the beneficial species of bacteria. It has 
not been determined with certainty to which genera these belong. Hiltner 
has proved first of all, that they are not the Alinit bacteria. In the end the 
usefulness will be decided by the greatest accomplishment of the nitrifying 
bacteria; for, according to Reitmair^ the nitrification in good mild soils with 
sufficient heat begins immediately after the fall harvest in such a way that 
the nitrate requirement of the subsequently planted grain will be met until 
the next spring. In this, however, a suitable friability and a definite calcium 
content is taken for granted". (See also the statements under Drain Water.) 
Naturally it must be emphasized with Stutzer^ that the land may be al- 
lowed to lie fallow only under certain fixed circumstances. It is thought 
that this may be done if it seems financially most advantageous for the agri- 
culturalist to do without the field for the long time while it is lying fallow, 
rather than to use the more quickly acting green manure and stable manure. 
When working with soils tending to unripeness, emphasis should be laid on 
this lying fallow only because it loosens the soil mechanically and does not 
affect the fertilizing salts. The nitrogen of the organic fertilizing masses 
seems, as Pfeiffer* especially emphasizes, to be held fast in the soil, capita- 
lized as it were, and then shows a long subsequent action. This author is, 
however, an opponent of the theory of letting ground lie fallow, which he 
characterizes as a robber cultivation, so far as the stock of nitrogen is con- 
cerned. He sees in this an incomplete restitution of the amounts of nutri- 
ment removed from the soil by the crops. In Pfeiffer's opinion, the soluble 
nitrogen compounds obtained by letting the land lie fallow are lost again in 
great part from uncultivated soils by the water which soaks through. Such 
considerations, in my opinion, are entirely justifiable for light soils, but do 
not hold good for heavy soils provided with an abundant absorptive power 
by the clay and weakened by the harvests. 

2. Relation of the Nutritive Substances to the Plants. 

The phenomena treated in this and the following division, are rarely the 
result of only a lack or an excess of the nutriment in the soil. They are 
usually the result of the co-operation of numerous factors, among which 
atmospheric humidity plays an especially decisive role. We will not forget 
that almost all diseases are produced by an unsuitable combination of the 



1 Reitmar, O., Die Stellung der Brache und der Griindiingung- in unsern moder- 
nen Fruchtfolgen. D. Landw. Presse. Sond. 1903. 

2 Wohltmann, F., Fischer, H., and Schneider, Ph., Bodenbakteriologische and 
bodenchemische Studien aus dem Poppelsdorfer Versuchsfelde. Journ. f. Landwirt- 
schaft 1904, p. 97. 

3 Stutzer, A., Die Nutzbarmachung des Stickstoffs der Luft fiir die Pflanzen. 
D. Landw. Presse 1904, Nos. 10-19. 

4 PfeifCer-Breslau Stickstoffsammelnde Baltterien. Brache und Raubbau. Berlin, 
P. Parey, 1904. cit. Centralbl. f. Agrik. Chem. 1905, p. 599. 



^75 

normal vegetative factors and are disturbances in the equilibrium of the 
interacting nutritive processes whereby certain ones are repressed while 
others predominate. 

If we now speak of diseases due to a lack, or an excess of moisture and 
nutritive substances we also involve in this the phenomena in which atrophies 
and hypertrophies occur in various parts of the plant body. These need not 
arise from an actual lack or excess of moisture and nutritive substances, but 
are simply produced by the unfitness of the plant, from the combination of 
the factors of growth, to nourish all its organs advantageously for the de- 
velopment of the whole. The absolute phenomena due to lack and excess 
are approximated on this account by the relative ones in the form of dis- 
turbances of the local equilibrium. 

A. Lack of Moisture and Nutritive Substances. 

a. Lack of Moisture. 

Influence of the Various Plant Coverings. 

After having considered the physical processes leading to a lack of 
moisture in the soil, and after having discussed a number of phenomena of 
diseases arising therefrom, we must consider supplementarily the influence 
which the covering of vegetation itself exercises on the water content of the 
soil. On the same soil, Avith the same atmospheric conditions, a cultivated 
plant will find a supply of moisture sufficient for its development on one 
part of a field, and not on another part, if on the former some species has 
been grown which makes a small demand on the water content. Therefore 
the preceding crop is of significance for each planting. 

As WoUny^ has determined, the water content is less in the root region 
of a planted field than in the corresponding layers of the naked soil. The 
more luxuriant the plant growth and the thicker and longer lived, the more 
water is lost from the soil. Experiments have not determined any fixed 
scale for the use of water, yet they indicate that, on an average, the ever- 
green conifers require the greatest quantities while deciduous trees and 
perennial fodder plants follow in a descending scale and the superficially 
rooting field plants make less demand on the whole supply of the water in 
the field. Of the latter group, the large, richly leaved, erect Papilionaceae, 
such as the field and bush beans, seem to require the most water at the time 
of their chief development, while the roots and tuberous plants cultivated in 
wide rows should be named last. In summer the perennial fodder plants 
use somewhat greater quantities than field plants and conifers. This is re- 
versed in the spring and fall. In winter the requirements of the different 
plants equalize, except the conifers, which in mild winter weather 
constantly withdraw definite amounts of water from the soil. 



1 "Wollny, E., Ueber den Einfluss der Pflanzendecken auf die Wasserfuhrung 
der Flusse. Vierteljahrsschr. d. Bayer, Landwirtschaftsrates 1900, p. 389. 



V. Seelhorst* treats the same subject and comes to the conclusion that 
so far as moisture is concerned, rye exhausts the field much less than wheat. 
This circumstance is very important when planting possible subsequent crops 
for green manuring, for, after wheat, which is cleared later from the field, 
this crop not only reaches the soil later, but also finds the soil much drier. 
Clover exhausts the water in the soil very greatly so that, aside from the fact 
that the soil easily becomes loosened by the clover stubble, in dry years, the 
winter crops following the clover can only develop slowly and unevenly be- 
cause of the lack of moisture. 

On the other hand, the potato, at least the variety ripening moderately 
early, seems to form a very good early crop, since it leaves the soil fairly 
moist. Peas also form a good early crop for winter grain. Oats are con- 
sidered by V. Seelhorst to be especially unfavorable, not so much 
because they exhaust the nutritive substances as because they remove water 
to so marked an extent. 

In connection with field plants, we should consider also the injurious 
influence of grass. It is easy to understand that a close turf keeps water 
from the roots of plants, especially fruit trees and impoverishes the friable 
soil, but recently a direct poisonous effect of grass- has been mentioned 
which may possibly be due to the fact that beneficial bacteria species are 
suppressed by it and injurious ones favored. In the case given, 
the roots of the apple trees were long, abnormally thin and browned, the 
leaves were very light in color and dropped 4 days earlier. The foliage was 
sparse, the wood growth scanty. As soon as the roots or even only a greater 
part of them reached soil not covered by grass the phenomena of disease dis- 
appeared. These phenomena agree essentially with those produced on heavy, 
impervious soils, with a scarcity of oxygen, so that it seems in no way neces- 
sary to assume any poisonous action. We find, in many cases, especially on 
light soils, that the turf does no injury, if care is taken to have nutritive sub- 
stances within reach of the roots. On close clay soils, the grass is kept green 
for a long time by the water rising by capillary action from the subsoil, 
thereby removing a great deal of moisture from the subsoil without return- 
ing it in quantities worth mentioning during the period of vegetation, since 
the grass uses the atmospheric precipitation itself. 

Wilting. 

In discussing "physiological wilting," mention was made of the fact 
that the phenomena of wilting can appear even with an abundance of mois- 
ture in the soil, since the roots function incompletely. In soils with a high 
content of soluble salts, the water, under certain circumstances, can be held 
so fast that the roots meet their need only with great difficulty. Phenomena 



1 V. Seelhorst, Untersuchungen iiber die Feuchteigkeitsverhaltnisse eines Lehm- 
bodens unter verschiedenen Friichten.* Journ. f. Landwirtsch. 1902. Vol. 50. cit. Cen- 
tralbl. f. Agr. Chemie 1903. Part 6. 

2 Bedford, Duke of, and Pickering, Spencer U., The effect of grass on trees. 
Third report of the Woburn exper. fruit farm. London, 1903. 



^77 

Then become evident, which can also be produced experimentally by the use 
of highly concentrated nutrient solutions : — short internodes, smaller leaves, 
short roots having a great tendency to decay, reduced production and trans- 
piration. A further cause of wilting is a lowered soil temperature. If a de- 
gree of heat is not reached wdiich is required by a certain plant so that the 
roots can begin absorbing the water, while the temperature of the air permits 
evaporation by the leaf apparatus, this disturbed equilibrium between water 
demand and supply makes itself felt by wilting. 

A special, not rare case, is the ivilting of hot bed plants when the pots 
are cooled during the re-working of the hot beds or during transplanting. 
Inexperienced gardeners then water the plants abundantly and the turgidity 
is restored if the water, previously warmed, awakens root activity. By a 
repetition of the cooling, the same experiment can be carried out until finally 
the pot is overloaded with water and the roots break down from a lack of 
oxygen. 

Another case of the wilting of potted plants was observed by Hellriegel. 
He found that plants wilted in large pots, which held three or four times as 
much water as small pots of plants of the same species, which did not wilt. 
This circumstance is explained by the relative water content of the soil, 
which in the small pots amounted to 14 to 20 per cent., while the absolute 
larger quantities of water in the larger amount of soil in the large pots was 
so disturbed that it represented only 11 to 15 per cent, of soil moisture. In 
this case, absorption was made more difficult for the roots in the larger pots, 
by the less easily transported water held more firmly in the capillaries of the 
soil, so that evaporation was in excess. 

In contrast to this physiological wilting we might term mechanical wilt- 
ing those phenomena due to an actual lack of soil moisture be- 
cause the mechanical transportation of water slackens in the ducts. Nat- 
urally with the great demand for moisture in the leaves and the scanty re- 
inforcement in the ducts, the air content increases and in this increase of the 
air content above a certain degree may be seen the arrest of the water cur- 
rent in the axial organs, as Strasburger^ emphasizes. In this, the air in the 
tracheal elements will be more dilute, as the transpiration and assimilation 
on warm days- are stronger, and the result is that a moistening of the soil 
becomes so much the more quickly effective. In general, watering exerts a 
lesser influence, the greater the turgidity of the plant '. The great tracheal air 
dilution shows itself also in the well-known fact, that field plants, wilting 
rapidly in hot weather, will stiffen from the dew on the soil at night, — 
especially since leaf evaporation is repressed at this time. 



1 Strasburger, Ed., Ueber den Bau und die Verrichtungen der Leitung-sbahnen in 
den Pflanzen. Jena 1891. cit. Bot. Zeit. 1892, p. 261. 

- Noll, Ueber die Luftverdiinnung in den Wasserleitungsbahnen der hoheren 
Pflanzen. Sitzungsber. d. Niederrheinischen Ges. f. Natur- und Heilkunde. Bonn 
1897, 11. p. 148. 

3 Chamberlain, Houston Stewart, Recherches sur la s6ve ascendante. cit. Bot. 
Jahresb. 1897, p. 73. 



278 

Change in Production Due to Lack of Moisture. 

The difference in the harvest yield, resulting from a lack of moisture, has 
also been considered in previous divisions, so that here we need cite supple- 
mentarily only a few other cases. Hellriegel's^ experiments are most de- 
cisive. Two tests of clover were taken from a field, in which, in places, the 
plants had begun to wilt. There was found : — 

In wilted plants Leaves 71.0 per cent, water, petioles 78.4 per cent. 

Leaves 71. i " " water, petioles 80.8 " " 
In turgid leaves among 

the wilted ones Leaves 82.5 " " water, petioles 90.0 " " 

The wilted leaves contained in the leaf-blades ca. 29 per cent, of dry 
substances; in the petioles, 19 to 21 per cent.; while the turgid leaves con- 
tained in their leaf-blades 17.5 per cent, and in the petioles 10 per cent., — i. e., 
only about half that of the wilted plants. 

An example of the influence of drought on grain is given by Prianisch- 
nikow's- investigations, according to which the nitrogen content increases in 
corn, if the moisture decreases. Stahl-Schroeder's^ studies give a more 
detailed representation of the influence exerted by the taking up of nutritive 
substances and their assimilation in dry years. After mentioning the well 
known fact, that phosphoric acid hastens ripening, while nitrogen and potas- 
sium delay it, he notes the importance of the months before blossoming for 
the taking up of the nutritive substances. If the soil moisture is deficient at 
this time, the organic substances will be in smaller quantity. But the nitric 
acid, which penetrates easily through the cell walls, will find its way into the 
plants and in its turn again incite the taking up of phosphoric acid, in order 
to effect the formation of the proteins. In this way, in dry years, scanty 
harvests are produced with a high nitrogen and phosphoric content. The 
nitrogen increase becomes the more evident, since, with drought, the grain 
stores up the starch with much greater difficulty. The reverse may be de- 
termined in the Norwegian corn tests, the high absolute weight of which is 
caused by an abundant starch deposit. This is explained by the growth of 
the grain with abundant moisture under the influence of the long days. 

In Hellriegel's experiments with barley, in pots filled with sand, we 
find, expressed in exact figures, the lowering of production, as the amount of 
moisture at the disposal of the plant is reduced. 

Soil moisture in percentages Dry Substance 

of saturation capacity. in Straw and Chaff in Grain 

80 — 60 7394 "^g- 4896 mg. ] averages 

60 — 40 5988 " 4133 " [ for 

40 — 20 4842 " 7942 " J 3 Plants 



1 Log. cit. p. 544. 

2 Prienischnikow, Ueber den Einfluss der Bodenfeuchtigkeit auf die Entwicklung 
der Pflanzen. Journ. f. experim. Landw. 1900. Vol. I, p. 19. 

3 Stahl-Schroeder, Kann die Pflanzenanalyse uns Aufschlufs iiber den Gehalt 
an assimilierenden Nahrstoffen geben? Journ. f. Landw. 1904. cit. Biedermann's 
Centralbl. f. Agr. Chem. 1905. Part 2. 



279 

The pots with a soil moisture under 20 per cent, of the saturation ca- 
pacity of the sand suffered so much from the summer heat, that the heads 
in the upper leaf sheaths stood still, without advancing to the formation of 
kernels. 

In apparent contradiction to such results stand the observations of 
practical agriculturalists that in perfectly dry, so-called dust-dry soils, the 
plants can keep on growing, although nutritive substances are entirely lack- 
ing in the subsoil (it is sterile). Such cases are explicable as soon as the 
sterile subsoil contains water and the roots remain in the moisture. Haber- 
iandt^ studied this case experimentally. He let the lower part of the roots 
of his experimental plants dip into distilled water, while the upper roots re- 
mained in soil layers, which, as shown by control experiments, were so dry 
that plants wilted in them. The plants of which the outermost roots dipped 
into distilled water showed a marked increase in dry substances ; from this it 
is evident that the roots found in the dry soil must have taken up the mineral 
substances. This division of labor by the roots explains the growth of our 
cultivated plants in spite of dry surface soil when their roots reach deep into 
a sterile, but moist, subsoil. 

According to Hellriegel, these changes in production, so well shown in 
grain, take place in the same sense in other cultivated plants. 

Discoloration of Woody Plants. 

The typical result of a lack of moisture and abundant illumination is 
the vigorous development of the mechanical tissues. We need refer only 
to the conditions found in dry climates. For example, Jonsson- reports that, 
among other characteristics of arid plants, the walls of the epidermal cells 
often become slimy. In Haloxylon, Eurotia, Calligonum, Halimodendron, 
layers of slime cork alternate with those of common cork. The slime cork 
is very capable of swelling and is laid bare after the protective cork splits, 
so that it can take up water and hold it. Cells containing slime are found 
also in the assimilatory tissues. In Halimodendron, the secondary bark 
often becomes thick and spongy, thereby modifying the temperature extremes 
and easily storing up water. In the peripheral parts, abundant secretions of 
salts form a protection. These characteristics vary in regions where the 
water supply is abundant in the soil and in the air. Thus, for example, no 
slime cork is found in Hahmodendron when grown in Copenhagen. 

Swanlund^ reports from new Amsterdam on the extremely thick outer 
walls of the epidermis, the frequent depression of the stomata, the rolling in 
of the leaves with the resulting restricted transpiration. We have touched 
upon this subject earlier in the divisions on differences in latitude and on 
the defects of sandy soils and at the same time have considered the nature of 



1 Cit. Biedermann's Centralbl. f. Agr. Chem. 1878, p. 314. 

2 Jonsson, B., Zur Kenntnis des anatomischen Baues der "Wiistenpflanzen. Lunds 
Univ.-Arsskrift XXXVIII. Bet. Jahresb. 1902, II, p. 292. 

3 Swanlund, J., Die Veg-etation Neu-Amsterdam's und St. Pauli's in ihren 
Bezieliungen zum Klima. Dissert. Basel 1901. 



28o 

the red coloration. By artificial interference, a localized lack of moisture 
and thereby a formation of anthocyanin is stimulated if the leaves of plants, 
of which a red autumnal coloration is characteristic, be nicked or the 
branches girdled. Then in the middle of summer a red color appears on the 
upper parts above the injury. 

In regard to the phenomena of discoloration produced by heat and 
drought, I will give some observations from 1892, in which year, in August, 
unusually high temperatures occurred together with hot winds. I found on 
the 19th of August a temperature of ^2.y°C on especially heavy loam soil. 
All the plants wilted and the majority gradually lost their foliage. Naturally 
great individual differences were also noticeable. 

The leaves became discolored and fell, the lowest leaves of the branches 
being the first affected. 

In the Alder, the leaves fell without losing their green color. 

Acer Pseudoplatanus var. Schwedleri, the under side of the leaf is red. 
From the tips backward the intercostal fields of the leaves turned a reddish 
brown to leather color. Besides this, deep brown, perfectly dry rust spots 
were scattered irregularly over the surface of the leaf. The injured leaves 
remained in place. 

Acer Negundo. The upper leaves were somewhat flabby. The edges 
of the leaflets were curled upward. The leaves next below were a pale yel- 
lowish green, the lowest light yellow, uniformly rolled up on the dry edges. 

Acer plantanoides. The leaves show on their under side oale yellow, 
irregular, small rust spots running into one another and extending ijetween 
the ribs. The dried tips bend upward like hooks. 

Fagus silvatica. On the various leaves, not always the lowest, but the 
most exposed, were irregular, dry places with yellow, faded edges in the in- 
tercostal fields. At times, the whole upper surface is equally lightly 
browned. There is never any outlining of the edges. 

Vitis vinifera. At the beginning of the drought, among the normal 
green leaves are found yellowish ones. The lemon yellow discoloration, red 
in other varieties, begins at one place on the edge and advances into the 
intercostal fields until only the veins seem green. In spite of the drought, I 
found on various lower leaves the dry, angular spots of Plasniopara viticola. 

Prunus Persica. All the leaves are somewhat languishing, some (but 
not always the lowest) turning yellow from the tips backward. On some 
trees, the discoloration advances more quickly along the veins so that at first 
the veining and then the rest of the surface of the leaf colors yellow-red to 
vvine-red. Then the leaves drop. (Peculiarity of the variety). 

Prunus domestic a. All the leaves are flabby. The majority, however, 
are still uniformly green with the exception of the lowest, which on many 
branches have become a whitish yellow and have slender, brown, reflexed, dry 
peripheral spots. Easily shaken off by the wind. 

Prunus avium. The lower leaves, especially on the short shoots 
(brachyblasts), turn a uniform lemon yellow and fall. 



28 1 

Prunus Cerasus. Only a few leaves turn yellow, otherwise the entire 
foliage is still fresh. A proof that the cherry loves drought. 

Pirns cotnniunis. According to the exposure rust spots are found in 
greater or less numbers showing, however, no yellowing. At times dry areas 
appear on the edges of the leaves, but more frequently the whole surface is a 
dark umber brown (the under side lighter in color with a still fresh green or 
lightly brownish mid-rib). The edges strongly rolled upward. Because the 
petioles remain green, the injured leaves do not fall at all or only much 
later. 

From these and numerous other observations it is evident that, on an 
average, the. parts of the leaves furthest from the veins discolor and dry first 
and most. When periods of heat follow one another rapidly with a strong 
sun action, the rust spots become very conspicuous ; with a lesser intensity of 
the sunshine, a general discoloration in the form of spots prevails. 

Here belongs also the especially strong development of anthocyanin in 
dry, poor localities, which becomes noticeable even in the arctic regions, 
where the red coloration with the strong illumination is a prevailing 
phenomenon. Wulff^ cites a very characteristic example. He found in 
places, fertilized by the excreta of birds, that the formation of anthocyanin 
disappeared in plants of which the xegetative organs seemed strongly redden- 
ed in arid regions. 

Finally, there must be considered the decrease in the power of move- 
ment of clover leaflets and related organs, with a continued lack of moisture 
In Mimosa piidica the periodic irritability is lost and the leaflets remain 
open, — -"drought cramp." 

The Red Coloration in Grain. 

The red coloration in grain in continued dry, hot summers has often 
called forth the theory that parasitic influences participated in it. Klebahn- 
tested more closely a special case, which was universally striking because of 
its wide distribution and intensity. He found that the red coloring matter 
appeared gradually in place of the cholorophyll. While the alcoholic ex- 
tract of normal leaves appears green, it is colored only slightly yellow in red 



1 Wulff, Thorild, Botanische Beobachtungen aus Spitzbergen, Lund. 1902. In 
regard to the theory at present generally held that anthocyanin is said to form a 
protection for the chlorophyll against an excess of light, Wuiff (p. 67) calls attention 
to Engelmann's investigations from which it is evident that the light absorption of 
the red anthocyanin is complementary to that of the chlorophyll and accordingly 
does not retard the decomposition of the carbon dioxid. "This fact has moreover 
proved most fully the untenability of the Pringsheim-Kny-Kerner theory of pro- 
tection from light." Wulff sees the advantage of the anthocyanin in its greater 
storage of heat. As I have mentioned already, I am unable to accept the above 
utility arrangements or the expi'essions of a "finality" in the organism and I per- 
ceive everywhere the necessary phenomena resulting from definite combinations of 
the factors of growth. The formation of anthocyanin seems to me to be the result 
of an excess of light on the cell content, rich in free acids, at the disposal of which 
there is no assimilate containing sufficient nitrogen. This condition can be pro- 
duced, as in plants of cold regions, by a lack of heat; in other cases by a scarcity 
of water, a decreased supply of nutriment, etc. 

- Klebahn, H., Einige Wirkungen der Diirre des Fruhiahrs 1893. Zeitschr. f. 
Pflanzenkrankh. 1894, p. 262. 



282 

leaves in which the cholorophyll has been destroyed. The red coloring mat- 
ter is soluble in water and glycerin, insoluble in alcohol and turpentine, 
turning blue with potassium and ammonia and again red with acids. It is in 
combination with the cell sap, partly in the epidermis, partly in the assimila- 
tary tissue. In oats, the development of the reddened plants and their grain 
production was proved to be less than that of green ones. We have just made 
a study of the reddening of grains^ and, in agreement with Klebahn, have 
come to the conclusion that in this redness only phenomena of a premature 
ripening are to be seen, together with a lack of moisture and great intensity 
of light. In our treatise will be found also anatomical details as to the 
blasting and the appearance of the so-called "drought spots." A yellow 
coloration of the walls of the bast fibres is worth noticing, which increases 
to a yellow brown, as is also the hardening of the cell contents in various 
groups of the assimilatory tissues. 

The death of leaves, due to sudden heat periods, should be distinguished 
from a normal death. The leaf does not shrivel up as completely as the nor- 
mally ripened one, — i. e., a leaf, the contents of which are nearly exhausted — ■ 
or it can do so only in places. In the normally ripened leaf, only the entirely 
impoverished cells of the leaf tissue, which therefore collapse to a waved 
folded layer, are found between the epidermis of the upper and of the lower 
sides, while in the former leaf just the remaining, more abundant contents 
stiffen the walls by drying, thereby more or less preventing the collapse. 

I also found the same discoloration phenomena in wild grasses (Arrhen- 
atherum) and expressed a warning against deceptions from anatomical in- 
vestigation. Especially angular or spherical masses appeared in. the contents 
which reacted with iodine like starch and thereby could give the appearance 
of a still existing, greater assimilatory activity. The other reactions prove, 
however, that "residue bodies" of the chlorophyll decomposition are here in- 
volved which belong to the carotin group. They could be compared with 
adipocere. 

"Reds" of Hops. 

The disease, called by practical growers "summer rust/' "Fox" or "red 
tan" consists in a spotting of the leaves, which advances from their bases. 
The spots attack the peripheral parts as well as the tissue groups lying 
between the different veins. By a partial destruction of the chlorophyll, the 
diseased places at first appear yellowish, then reddish and finally dry and 
browned. In the meantime the leaf continues longer in a wilted condition, 
finally, it shrivels and drops off, while the upper, younger parts of the vine 
are still fresh, green and developing. The new structures produced during 
this time are smaller in comparison with those of other plants which are un- 
affected and have not lost the lower leaves. If the disease remains restricted 
to the lower parts of the vine, the injury is not important; but, if it attacks 



1 Sorauer, P., Beitrag zur anatomischen Analyse rauchbeschadigter Pflanzen. 
Landw. Jahrb. 1904, p. 596, Plates XV to XVIII. 



283 

the upper portions with the blossoming catkins, the harvest will be very light 
and an immediate gathering is advisable. 

The disease may be confounded easily with the "copper rust," caused by 
the weaver moth, but is distinguished by its location since the copper rust 
colors the leaves on the upper part of the vines a reddish yellow and is 
recognizable from its finely spun threads on the underside of the leaf, while 
the summer rust causes a yellowing and drying of the leaves, beginning at 
Ihe base of the vine. It is a sapping of the older organs by the younger 
ones, which require the organic material there present for their further 
development. 

The so-called "Pole Red" seems to correspond to the "blast" of grain 
and to be the result of a sudden dry period when the catkins mature. 

In this and the related diseases of reddening the lack of atmospheric 
moisture plays an especially decisive role, because watering only the soil 
rarely proves a remedy. It is better, if possible, to water regularly in the 
evening. But for larger areas in practical cultivation the necessary number 
of laborers and the great quantities of water may rarely be had. Hence re- 
sort must be had to preventative measures, in which either the excessive 
evaporation is reduced by extensive shading, or the saturation capacity of the 
soil is increased by the supply of fertihzing salts (not animal manure). Fr. 
Wagner^ cites an example for the later case. He found in his cultivation 
that hop vines, without having been given nitrates, did not resist drought 
and vegetable or animal parasites so well as those fertihzed with chili salt- 
petre and also their lower leaves turned yellow earlier. In the same way it 
lias often been observed in practical agriculture that fodder and sugar beets 
withstand drought better when the soil has been fertilized with potassium 
salts or nitrates, or even with abundant stable manure-. 

Similar discoloration resulting from a lack of moisture has been ob- 
served in flax. This is described partly as the "Reds" (le rouge) and partly, — 
when the points of the stems turn yellow prematurely, — as the "yellows" 
(le jaune). 

"Leaf Scorch" — "Parching of Vines" — "Red Scorch." 

The above are collective names for a group of phenomena distinguished 
with difficulty from one another, in which the leaves are colored red. As a 
rule, the discoloration is followed by a partial or complete drying up of the 
foliage, which begins to fall prematurely. Recently Miiller-Thurgau^ has 
determined a parasitic cause for a definite form of reddening* and takes 
pains to emphasize the characteristics, apparent to the naked eye, distinguish 



1 Wagner, Fr., Salpeterdiingungsversuche des Deutschen Hopfenbau- Vereins 
Wochenbl. d. Landw. Ver. in Bayern 1904, p. 182. 

2 See, for example, .Tahresb, rt. S'M-idermi'^schu^Fes f. Tflanzenschutz flir das 
Jahr. 1904. Arb. d. Deutsch. Landw.-Ges. 1905, p. 91. 

3 Miiller-Thurgau, H., Der rote Brenner des Weinstocks. Centralbl. f. Bakt. II, 
1903. Parts 1-4. 

4 Another form of Red Scorch connected with Botrytis vegetation is described 
by Behrens (Untersuchungen iiber den Rotbrenner der Reben) in Ber. d. Grofsh. 
Bad. Versuchsanstalt zu Augustenborg 1902, p. 43. 



284 

ing this disease from others. With reference to the form of "Red vScorch," 
described in the second volume of this manual and caused by Pseudopeziza 
fracheiphila (see Vol. II.,, p. 278*) in which the discoloration often begins in 
the form of spots in the angles of the veins, it should be emphasized here 
that the leaf scorch, which is due to a lack of moisture together with strong 
sunshine, begins as a rule with a discoloration of the intercostal fields start- 
ing from the edge. The phenomena vary greatly, according to the variety 
and habitat, and at times only a shining yellow color is found instead of the 
reddening. The edges of the leaves often dry up. The kind of discoloratioji 
runs parallel with the progress of the summer blight in other woody plants, 
whereby it may usually be observed how the deficient moisture supply be- 
comes evident at first on the parts lying furthest away from the petioles and 
the mid-rib and then advances until finally only the immediate surroundings 
of the veins remain green. (See Changes due to place of growth.) 

In regard to the physiological activity, Miiller-Thurgau had proved 
earlier that the formation of starch and its solution took place the more 
slowly, the less the water content of the leaves^ ; irrigated ^•ines formed more 
sugar. 

A phenomenon manifesting itself like the parasitic scorch has been de- 
scribed by Sauvageau and Perraud- as the pectin disease (maladie pectique), 
the result of continued drought. In this, the leaf blades are loosened from 
the petiole. 

Yellowing Due to the Grafting Stock. 

In our species of fruit there is often a lack of water, because a rapidly 
growing variety grafted on a dwarf stock, in times of great evaporation, is 
not able to convey the necessary water to the graft. 

On good soils pears, grafted on quince stock, often turn yellow, while 
trees on wild stock thrive well. In dry summers I found with such dwarf 
trunks that well grown scions, inserted later in the bark, formed strong but 
yellowish shoots, while the older top was green. In this too I see phenomena 
of the lack of moisture due to the quince stock which (especially if planted 
shallow) cannot obtain the necessary water. Pears on shallow planted 
quinces ripen their foliiu/e more quickly and lose if earlier. 

Premature Drying of the Foliage. 

When the foliage dies as a result of the summer drought, in which it 
usually hangs on the branch, because the petiole has remained fresh, the 
injury suffered by the tree is far greater than is generally understood. 

It is thought that the injury consists primarily in the premature stopping 
of leaf activitv and the lessened formation of wood. Kraus'" investigations 



* Paging: in the German original. 

1 HI. Jahresber. d. ^'ersuchsstat. Wadensweil. Ziirich 1894. p. 56. 
- Sauvageau, C. et Perraud, .J.. La maladie pectique de la vigne. Revue de 
viticulture 1894, p. 9. 

3 Bot. Zeit. 1873, Nos. 26 and 27. 



285 

have proved, however, that, besides this lack of additional growth, a positive 
loss in substance takes place, which is much greater than in normal fall de- 
foliation. The leaves killed by blight do not behave as do those which drop 
off in the fall. These have gradually given up to the trunk most of the sub- 
stances still utilizable for the plant body and in the end have been loosened 
by a round-celled layer of separation. The dried leaves, in which no such 
layer has been formed, retain tlie elements which contain nitrogen together 
with phosphoric acid and only the starch with the potassium reaches the 
trunk before the death of the leaf. By the premature drying of the foliage 
approximately twice as much nitrogen and phosphoric acid are lost to the 
plant as by the autumn leaf-fall. This is proved by analysis of the leaves 
of a syringa carried through by Maerker. 

In percentages of dry substances, there vvas contained in 

Summer blighted leaves Autumn fallen leaves 

Nitrogen 1-947 i-37o 

Phosphoric acid 0.522 0.373 

Potassium 2.998 3-831 

Calcium 1.878 2.416 

All mineral substances 

(free from carbon dioxid) 8.028 9-636 

The above amounts, if expressed in percentages of the whole ash, would 
be as follows :- — • 

Summer blighted leaves Autumn fallen leaves 

Nitrogen 24.0 14.0 

Phosphoric acid 6.5 3.8 

Potassium 37.3 39.7 

The Burning Out of Grass. 

With the drying of the turf, as the result of hot periods in summer, the 
loss of nutritive substances must be considered especially in ■ meadows. 
Where there are no irrigating arrangements, there is no possibility of avoid- 
ing the injury. In ornamental planting, howe\'er, it may be avoided if the 
action of the light and thereby evaporation is repressed at the right time by 
mulching with hay or other light shading material. Sprinkling the grass 
surfaces is effective only when it can be carried out repeatedly during the 
day. In other cases, shading must be resorted to. 

Silver Leaf. 

The "Silver Leaf" belongs among the phenomena which have not yet 
been tested experimentally in regard to their causes and therefore can be 
classified only provisionally. 

The disease so manifests itself in fruit trees that the leaves, otherwise 
normally developed, lose their dark green appearance and give a silvery, 
whitish reflection. As a rule only individual branches suffer and possibly 



286 

after June or July. In the following year, or in the second, at the latest in 
the third year, after the appearance of the silver leaf, the branch dies. In 
the specimens which I could examine after the lapse of a year, the 
phenomenon appeared often on the other branches after the dead branch 
had been removed, so that, for the present, I have formed the hypothesis 
that the silver leaf is an absolutely certain precursor of the death of a branch. 
It is found most wide-spread among apricots. I found the phenomenon 
also in plums and apples. 

The change begins in the older leaves of the spring growth, the youngest 
more often escape ; likewise the late shoots developing suddenly in old wood 
from preventative eyes. First of all only a certain dullness of color is 
found, a loss of the gloss in places and, as it seems to me, an increased 
amount of air in the intercellular spaces between the various palisade cells 
or between them and the epidermal cells. Gradually the dull places become 
whitish, in fact because of a glandular breaking up of the epidermal cells 
between the finest ramifications of the veins which remain green. This 
loosening up consists of a dissolving, in places, of the connection between 
epidermis and palisade parenchyma. 

Aderhold^, who also observed the disease in cherries and found that the 
cells of the epidermis mutually separate from one another, could prove that 
the variations from the healthy leaf, in places displaying the silver leaf, were 
found in the solvability of the intercellular substances (middle lamellae). 
He surmised that the intercellular substance in the diseased organs consisted 
of more soluble pectin compounds than in the the healthy leaf and, since the 
calcium compounds of pectic acid represent insoluble conditions, the theory 
is pertinent, that the disease may be due to a lack of calcium. 

According to this theory, the disease would also belong in the group of 
phenomena, due to deficient moisture and nutritive substances ; only it must 
be emphasized in this, that the content of moisture and nutritive substances 
in the soil cannot come under consideration here, but that only in the plant 
itself can it be manifested locally. And this circumstance points to dis- 
turbances in the vascular system. This is favored also by the fact that the 
branches with silver leaf die prematurely. 

The apricots and plums which I observed showed gummosis and the 
apple trees suffered from the gnawing of bark beetles. It might be possible 
to strengthen the whole organism by rejuvenescence of the diseased trees 
and by supplying calcium. 

The Water Core of Apples. 

In the same way the phenomenon may be traced to the local vascular 
disturbances in which individual fruits of a tree in part, or as a whole, re- 
main hard and become glassy and transparent, — develop less color and are 
tasteless. 



1 Aderhold. R. Notizen iiber einige im vorigen Sommer beobachtete Pflanzen- 
krankheiten. Zeitschr. f. Pflanzenkrankh. 1895, p. 86. 



287 

In investigating an apple, which was only partially glassy, I found in 
longitudinal section, that the particles of the skin were most intensively 
glassy and that, inside the fruit, the white, normal flesh extended from the 
base pretty nearly to the bud end. The glassy zone had a whitish marbling 
due to wedged-in groups of normal flesh. The seeds were mostly deformed, 
not ripe and still white. The healthy part contained abundant starch and 
intercellular spaces strongly filled with air. These spaces were poorer in air 
in the glassy part and there was no starch except in isolated, wedged-in cell 
groups. The glassy part turned brown more quickly in the air ; some dex- 
trin could be found together with abundant grape sugar. In dry- substances 
there was found in 

The healthy half The glassy half 

With the skin 21.48 per cent. 19.43 per cent. 

Without the skin 20.24 " " 17.97 " 

Aderhold^ found in 

Healthy fruit flesh Glassy fruit flesh 

Specific gravity O.718 0.925 

Dry substances in percentages of the 

fresh weight 14-44 per cent. I2.6n per cent. 

Ash in percentages of the dry 

weight 2.093 pei" cent. 1.76 per cent. 

Malic acid in 100 ccm. juice 0.92 g. 0.53 g. 

The most recent determinations come from Behrens". He found in 

100 ccm. of Water Invert sugar Acid 

Pressed juice of the normal apple 87.38 g. S-^S g. 0.56 g. 

Pressed juice of the partially glassy 

apple 88.06 g. 4.40 g. 0.47 g. 

In agreement with my statements, the above figures show that the flesh 
of the glassy apple is considerably poorer in acid, dry substances and ash. 
The glassy appearance and the smaller size is explained by the fact that the 
intercellular spaces of the glassy part are filled with water and the cells are 
smaller. 

Practical growers believe they have observed that the following varie- 
ties tend especially to the production of glassy fruits : — Zurich Transparent 
apple, Gloria mundi, white Astrachan and Virginia summer Rose apple. On 
an average, in the first year of bearing, the little trees were more disposed to 
the production of such fruits than in later years. 

b. Changes in Productton Due to Lack of Nitrogen. 
Starvation Conditions in Cryptogams. 

In reference to the parallelism of phenomena in lower and in more high- 
ly organized plants, an example may be cited first of all from the fungi. 

1 Aclerhold, loc. cit.. p. 8. 

2 Behrens, J., Bericht d. Grofsh. Bad. Landes-Versuchsanstalt Augustenburg i. 
J. 1904, p. 53. Karlsruhe 1905. 



288 

Fliorow^ tested the effect of starvation on respiration in Mucor and Psalliota 
canipestris. In Mucor, respiration immediately falls to a great extent be- 
cause in this fungus there exists no storage of reserve stuffs in the mycel- 
iium. In the fruiting body of the basidiomycete, however, there is a great 
deal of reserve material and, for this reason, it is very independent of the 
nutritive substratum so that its respiration only falls very slowly with star- 
vation. In regard to the exchange of the proteins, Fliorow concludes from 
experiments with Amanita muse aria that the percentage of nitrogen as a 
whole increases during starvation chiefly because the substances free from 
nutritive substratum so that its respiration only falls very slowly with star- 
takes place, which is simultaneous with the periods of spore formation and 
ripening. A rapid decomposition of the protein follows at once. 

To be sure, the production of carbon dioxid and the taking up of oxy- 
gen gradually decrease in the starvation of fungi, but in unequal propor- 
tions, as was observed by Purjewicz-, with Aspergillus niger. 

PrantP has given very good experimental observations on the prothallia 
of ferns. His experience shows especially that, in the seeding of fern 
spores, the most diverse variations occur in the prothallia. Some of them 
have a tissue capable of developing further (meristem), while others lack 
it and therefore are "ameristic." Earlier investigations* had shown Prantl 
that the ameristic condition can occur with too small supply of air as with 
a scanty supply of water and indeed also of mineral substances^. The ob- 
servation, that under the most favorable conditions of illumination, ameristic 
individuals appear when the prothallia grow too close, led to the experiment 
of testing directly the influence of the nitrogen supply. Spores of the rapidly 
germinating Osmunda regalis and of Ceratopteris thalictroides were sown on 
different nutrient solutions. It was thus shown that the spores, germinated 
in distilled water, produced ameristic prothallia. They formed surfaces of 
15 to 25 cells of pretty uniform size and similar content. The chlorophyll 
grains were poor in starch. On the other hand, the prothallia grown in a 
nutrient solution, free from nitrogen, but otherwise normal, were dis- 
tinguished by an extremely large starch content, but otherwise resembled the 
individuals grown in distilled water. Only the specimens grown in a nutri- 
ent solution with a nitrogen admixture (0.64 per cent, ammonium nitrate) 
v/ere meristic. If specimens of meristic prothallia were transferred into a 
nutrient solution free from nitrogen, the meristem disappeared after 14 days, 
while the cells as a whole increased, had divided here and there and had been 
filled with starch. If, on the other hand, ameristic prothallia were placed in 



1 Fliorow, A., Der Einflufs der Ernahrung auf die Atmung der Pilze. Bot. Cen- 
tralbl. 1901. Vol. 87, p. 274. 

2 Purjewicz, K., Physiolog-. Untersuch. iiber die Atmung der Pflanzen. cit. Bie- 
derm. Centralbl. 1902, p. 180. 

3 Prantl, Beobachtungen iiber die Ernahrung der Farnprothallien und die Ver- 
teilung der Sexualorgane. Bot. Zeit.. 1881, p. 753. 

4 Flora 1878, p. 499. 

5 Reed has shown (Annals of Bot. 21; 501, 1907) that prothallia of G. sulphures 
were unable to form archegonia where calcium was absent. Translatoi*. 



289 

a complete nutrient solution, they at once formed a meristem on their outer 
edges by a repeated cell-division, while the starch supply decreased. 

The distribution of the sexual organs varies according to the nutritive 
conditions. Ameristic prothallia bear only antheridia, never archegonia, 
which are associated with the presence of a meristem. Of especial impor- 
tance at this point is Prantl's observation that ameristic prothallia of Os- 
munda, which had borne isolated antheridia, developed abundant archegonia 
after nitrogen had been supplied; besides the archegonia, antheridia also 
appeared. 



PART IV. 



MANUAL 



OF 



PLANT DISEASES 



BY 



PROF. DR. PAUL SORAUER 



Third Edition—Prof. Dr. Sorauer 

In Collaboration with 

Prof. Dr. G. Lindau And Dr. L. Reh 

Private Docent at the University Assistant in the Museum of Natural History 

of Berlin in Hamburg 



TRANSLATED BY FRANCES DORRANGE 



Volume I 
NON-PARASITIC DISEASES 

BY 

PROF. DR. PAUL SORAUER 

BERLIN 



WITH 208 ILLUSTRATIONS IN THE TEXT 



Copyrighted, 1915 

By 
FRANCES DORRANCE 



1^,^- 



SEP II 1916 



<e)CI.A43.S315 

THE RECORD PRESS 
Wilkes -Barre, Pa. 



"Vvt? 



.^1 



3' 



289 

a complete nutrient solution, they at once formed a meristem on their outer 
edges by repeated cell-division, while the starch supply decreased. 

The distribution of the sexual organs varies according to the nutritive 
conditions. Ameristic prothallia bear only antheridia, never archegonia, 
which are associated with the presence of a meristem. Of special impor- 
tance at this point is Prantl's observation that ameristic prothallia of Os- 
munda, which had borne isolated antheridia, developed abundant archegonia 
after nitrogen had been supplied; besides the archegonia, antheridia also 
appeared. 

From these changes produced by the nutritive substances is explained 
without forcing the tendency to "dioecia" ascribed to some ferns by 
various authors ; by Millardet^ for Osmunda, by Bauke- for the Cyatheaceae 
and for Platycerium, and by Jonkmann" for the Marattiaceae. 

H. Hofifman* cites further notes pertinent here ; first of all, Von Ilof- 
meister, who assumes that in Equisetum the prothallia produce decidedly 
more antheridia in the light and in a dry locality, i. e.. bear more male plants 
since the prothallia are almost entirely dioecious. 

Borodin found that germinating spores of Allosurus Sagittatus de- 
veloped antheridia when placed in the dark. 

The Production of Sterile Blossoms. (Sterility.) 

Sterile blossoms in phanerogams are due primarily to a lack of nitro- 
gen. This may manifest itself in very different ways ; as already mentioned 
in the blasting of grain, a sufficient supply of nitrogen may be present in 
the soil but as result of a prolonged, intense drought there is lacking the 
carrier, the water, to bring to a further normal development the already 
differentiated stamens and pistils. On the other hand there may be in heavy 
seeding a struggle for nitrogen in which the plants that earliest attain most 
vigorous vegetative development take the nutriment from the less vigorous 
ones. In a consideration of sterility there must further be taken into ac- 
count the cases where the existing nutritive material is used up in some 
other way, so that a one-sided increase or decrease of a growth factor favors 
the vegetative utilization of the elaborated organic material to such an ex- 
tent that nitrogen sufficient to mature the sexual organs is lacking. Finally 
it not infrequently happens that the material is abundantly used in the de- 
velopment of the lesser nitrogen requiring male organs and no longer 
suffices for the development of the ovary. The cases among phanerogams 
where starvation conditions induce blossom development are not in opposi- 
tion to this view. Examples of this are found in our fruit trees, where dis- 
eased specimens with a pronounced decrease of shoot development "bloom 
themselves to death." In horticultural practice plants are purposely starved 
in order to attain flower production {Kantua de pendens, Correa, etc.) 



1 Pring-sheim's Jahrbiicher, X, p. 97. 

2 Bot. Zeit. 1878, p. 757. 

3 Extrait des Actes du CongrSs international. Amsterdam, 1877. 

4 Hoffmann, H.. Zur Geschlechtsbestimmung, Bot, Zeit. 1871. Nos. 6 and 7. 



290 

Lovers of cacti sometimes pull their plants from the pots in winter and let 
them shrivel, so that they may bloom more freely. In this case nitrogen is 
not lacking but the scarcity of water causes the plants to make use of the 
elaborated food in flower production. 

In treating of the bearing of sterile blossoms, due to insufficient water, 
Oberdieck^ reports that, as a result of drought, the blossoms of large- 
flowered pansies drop prematurely while, with sufficient moisture, they 
develop the seed capsules. Double zinnias behave in the same way, like- 
wise the red flax and often, indeed. Phlox Drummondii. Garden beans do 
not set so well in dry years. Raspberries and strawberries give small, poorly 
seeded fruits. In the case of the ever-flowering wood strawberry there is 
a degeneration with continued drought, making the plants resemble the 
"Vierlander strawberries," since they no longer develop fertile blossoms. 
Zacharias- states that the latter variety of strawberries is one which is 
usually either staminate or pistillate, but rarely monoecious. He is of the 
opinion that pollination is incomplete where only a few staminate, so called 
"wild" plants, distinguished by their weaker growth, weaker runners and 
lower growing inflorescences with larger blossoms, are present on the fields. 
He emphasizes the fact that invariably few pistils develop, so that only a 
portion of the swollen receptacal is covered. We would lay the chief weight 
on the latter point and advise remedially a change of soil and variety. 
Zacharias recommends putting more staminate plants among the pistillate 
ones. 

Phenomena similar to those in the Vierlander strawberry have been 
observed in the black currant^. The sterility is said to be caused neither by 
dryness nor by a shady position, but is ascribed by practical workers to a 
varietal peculiarity. Likewise complaints are made as to the scanty setting 
of fruit in the Schattenmorelle (shadow Amorelle cherry). The "Praktische 
Ratgeber" (Practical Adviser) advises in grafting the taking of scions only 
from the trees of that variety which experience has proved to bear well. 
We often meet with such indications of the inheritance of undesirable 
peculiarities. 

Numerous statements may be found in regard to the increasing pre- 
dominance of staminate over pistillate blossoms. One of the earliest is 
the statement by Knight, that melons and cucumbers at higher temperatures 
without sufficient light almost always produce only stamens. Manz*, in his 
experiments, comes to the conclusion that in monoecious as well as in 
dioecious plants drought favors the development of male plants, while 
moisture and good fertilization favor female plants. It is said that male 
plants can be made to bear perfect blossoms by removing whole branches. 
This might then indicate that the nitrogen taken up by the roots is now dis- 
tributed among a lesser number of blossoms and thus better nourishes these. 

1 Oberdieck, Deutschlands beste Obstsorten, p. 9 footnote. Leipzif, 1881. 

2 Zacharias, E., tJber den mang-elhaften Ertrag der Vierlander Erdbeeren. Verh. 
d. Naturw. Vereins, Hamburg, 1903. 3. Folg-e, XI, p. 26. 

3 Prakt. Ratgeber im. Obst- und Gartenbau. Frankfurt a. O., 1904, No. 10. 

4 Vierte Beilage zur Flora, 1822, Vol. V (after Hoffmann loc. cit.), p. 88. 



^9t 

Conditions are similar with our fruit trees, most of which rest a year, 
that is to say, bear one year a smaller crop and then the next a larger one. 
After a heavy crop the trees are usually so exhausted that they need one 
year in order to store up sufficient nutritive substances for the next crop. 
Hoiifman^ mentions further that many trees (the horse chestnut and the 
Scotch Pine) exhibit a normal alternation of sexes, since they bear staminate 
flowers one year and perfect ones the following. The increase of carpels 
in the giant poppy (Papaver somniferum forma poly car pica monstrosa) 
occurs only in the most vigorous plants. During his travels Karsten^ found 
that the palms growing in swamps and damp woods, as a rule, bear perfect 
blossoms, but become polygamous again from a lack of nutrition. The 
genera growing on dry cliffs or arid plains have ordinarily but not naturally 
separated sexes, and these bear staminate and pistillate flow^ers on separate 
branches. At the beginning of the dry season the fruit ripens, requiring a 
great deal of nutritive material, and then only staminate flowers develop; 
while after the dormant period, at the beginning of the rainy season, pis- 
tillate blossoms are formed in great abundance. 

Cugini^ found in star\'ed plants of maize, which he obtained by heavy 
seeding, that various individuals bore only staminate flowers. De Vries* 
was also able to demonstrate the inheritance of sterility in the case of maize. 
He took seeds from plants in which the pistillate inflorescences were entirely 
wanting or extremely weak and obtained in the first year 12 per cent, of such 
imperfect plants. The sowing of the following year yielded 19 per cent, of 
sterile plants. 

A case described by Muller-Thurgau^ shows that aside from nitrogen 
hunger sterility can often be due to a lack of moisture alone. He found 
the stigmas on fruit trees so dry that the pollen grains could not germinate. 
In comparative test experiments with pears, trees which had been abundantly 
watered during the time of blossoming exhibited an evident increase in yield. 
Not only did numerous blossoms on the unwatered trees fall, shortly after 
the time of blossoming was past, but even the young fruits, when about the 
size of cherries, fell in strikingly large numbers. On trees standing in dry 
places, usually one fruit remained to each umbel, while in the case of water- 
ed trees, on an average, three developed. 

But sterility occurs even with good pollen and with stigmatic conditions 
favorable for germination. Waite" in his experiments on pear blight kept 
insect visitors away from the flowers and found that the fruit set to a very 
small extent. Further investigations convinced him that certain varieties 
of pears and apples cannot be fertilised at all by their own pollen (nor by 
that from other individuals of the same variety), but that the pollen from an- 



1 Bot. Zeit. 1882, p. 508. 

2 Linnaea, 1857, p. 259. 

3 Cugini, Intorno ad un anomalia della Zea Mays. cit. Bot. Centralbl. 1880, p. 1130. 

4 de Vries, H., Steriele Mais als erfelijk Ras. Bot. Jarbook II, p. 109. 

5 III. Jahresber. d. Versuchsstat. Wadensweil. Zurich, 1894, p. 56. 

6 Cit. Galloway, B. T., Bemerkenswertes Auftreten einiger Plflanzenkrankheiten 
in Amerika. Zeitschr. f. Pflanzenkrankh. 1894, p. 172. 



2^2 

other variety was necessary for this. This would explain the observed 
sterility in large fruit orchards composed of a single variety. 

Ewert^ acknowledges that self-sterility has been determined for many 
species, but is of the opinion, nevertheless, that large plantations of only one 
variety do not fall behind those made up of mixed varieties, because cross- 
pollination will be secured promptly by honey and bumble bees. The setting 
of the fruit fails only if, because of unfavorable weather, the insects are 
unable to fly. 

According to our theory there should also be noted in this connection 
the alternation between chasmogamic flowers (sterile with large petals), 
and cleistogamous flowers (fertile with aborted petals). With E. Loew", 
we perceive in these conditions no mutations in de Vries' sense, but simple 
variations which depend on the form of nutrition. Goebel found that 
cleistogamous flowers formed earlier and he was able, by keeping them 
dry and exposed to abundant sunshine, to force violets which had previously 
borne cleistogamous flowers, to form chasmogamic blossoms in July, which 
is a very unusual occurrence at that time of year. The alternation was 
called forth by the postponement of the use of the plastic food material at 
hand. The cleistogamous bud cannot develop with a lack of moisture and 
abundance of light and the plastic building materials then remain at the 
disposal of later produced blossoms. Since in these the pistils are rarely 
formed and do not mature, the material is free for the especially vigorous 
development of the petals which need the light. 

Seedless Fruits. 

Sterility is often connected with the appearance of seedless fruits, and 
can in the same way become a peculiarity of the variety. 

In a new American variety of apples (the "Wonder of Horticulture") 
this charactistic has recently been considered an especial recommendation 
of the variety^, since the blossoms yield fruit without having been fertilized. 
In this way, the harmful agents threatening other varieties at the time of 
blossoming, such as frost, mist, rain, drought, poor insect pollination, etc., 
are avoided. The new variety has no corolla and to this fact is attached the 
hope that blossom pests and other insects, which would be attracted by the 
petals, may spare such flowers. 

Seedless varieties of fruits, i. e., those in which poorly matured seeds 
are found, have been known from the earliest times as, for example, the pear 
"Rihas Seedless," ("Rihas Kernlose") and the Seedless Father Apple 
("Vaterapfel ohne Kern") It is said that it frequently happens that vari- 
eties free from seeds appear from grape seedlings, unfortunately dis- 
tinguished, however, by their small size and the great hardness of the 
grapes. 

1 Ewert, Welche Erfahrungen sind gemacht in bezug auf geringere Frucht- 
barkeit, etc. Proskauer Obstbau-Zeitung, 1902. 

2 Loew, E., Bemerkungen zu W. Burck's Abhandlung iiber die Mutation als 
Ursache der Kleistogamie. Biol. Centralbl. XXVI, 1906, Nos. 5-7. 

3 Janson, A-, Der kernlose Apfel. Gartenflora, 1905, p. 490. 



293 

The production of seedless fruits is mentioned often in the more recent 
works. Kirchner^ who also cites Waite's" observations, declares that 
typically and normally developed fruits are obtained only by crossing with 
the pollen of a different variety. The largest fruits are always produced by 
cross-pollination. Pears produced by self-pollination developed at times 
almost no seeds. The flowers exposed to the visits of bees, or artificially 
cross-pollinated, on the contrary, yielded fruit with abundant healthy seeds. 
Thus it would be advisable to grow a mixture of varieties. 

In opposition to this theory, Ewert.^, even in his latest papers, holds to 
his point of view, advocating for practical reasons the cultivation of a 
single variety in blocks. 

In regard to seedless grapes, we will refer to the investigations of 
Miiller-Thurgau*. Ewert emphasizes, in reference to seed-bearing fruits 
that, for the setting of the fruit, the amount of organic material at 
the disposal of the individual blossoms is of especial importance. In various 
cases a better nutritive condition for the individual blossoms can be obtained 
artificially by ringing, since they vary in their development. The pistils 
are either greatly developed and project as much as one centimeter /above 
the anthers (protogyny), or both sexual organs are equally long (homog- 
any), or the pistils are shorter than the stamens (protandry). Ewert's 
experiments do not confirm absolutely the conclusion that the stronger pro- 
togny is developed, the more the blossom, which is consequently self-sterile, 
demands the pollen of some other variety, and, conversely, the more homog- 
any and protandry manifest themselves, the greater the possibility of self- 
pollination. It is evident that the organic nutriment is carried first of all to 
those fruit buds, in which cross-pollination has made seed formation possible. 
In comparing fruits containing seeds and those without seeds on the same 
tree, the seedless ones are smaller and are often malformed. If seedless fruits 
alone are produced on a tree, by keeping away all foreign pollen, they attain 
the same size as do those bearing seeds. Probably fruits can also be pro- 
duced without the action of pollen. 

In some cases fruits can be observed in which the core does not exist, 
or is scarcely indicated. In reference to the former, Burbidge^ reports that 
pears without seeds and core represent very solid parenchymatous fruits, 
said to be larger, better flavored and' possessing a better keeping quaUty 
than pears containing seeds. 

I, myself, some years ago, received a branch of pears, one specimen of 
which is given half-size in Fig. 36. The fruits were perfectly hard and 



1 Kirchner, O., Das Bliihen und die Befruchtung- der Obstbaume. Vortrag-. Ref. 
Zeitschr. f. Pflanzenkrankh. I'JOO, p. 297. 

2 Waite, Merton B., The pollination of the pear flowers. Washington, 1894, 
U. S. Dept. Agric. Bull. 5. 

3 Ewei-t, Blutenbiologie und Tragbarkeit unserer Obstbaume. Landwirtsch. 
Jahrbucher, 1906, p. 259. 

4 Miiller-Thurgau, Folgen der Bestaubung- bei Obst- und Rebenbliiten VIII. 
Ber. d. Ztiricher Bot. Ges. 1900-1903. 

5 Royal Horticultural Society of London. Cit. Bot. CentraJbl. 1881. Vol. VIII, 
p. 319. 



294 



healthy until injured by the autumn frosts. At A we see a normal woody 
branch ; at 5 a branch, the terminal bud of which is swollen up to a seedless 
fruit ; at C is shown a fruit grown from a lateral bud with primordia of 
core ; n is the scar of a fallen leaf ; s an undeveloped lateral bud ; k a per- 
fectly matured leaf bud on the fruit stem ; sch scale-like leaf on this stem ; 
at g are the normally extended vascular bundle fibres, arranged about the 
compartments of the core (/) enclosing the rudimentary ovules. At c are 
visible the dried remains of the calyx and at st the branches of the style. 

This case differs from the one described by Burbidge and from most 
others described as yet, in that the fruit is the product of the buds of the 
current, not of the previous year. Tt is not rare for the pear to bear 

occasional fall fiowers. They can, in 
fact, arise from buds set the previous 
year, as is often stated, but, as yet, I 
have had opportunity to observe only 
such blossoms as were produced on 
the branches of the current year, ma- 
tured in the summer, a fact which 
could be determined easily from the 
wood ring of the branch bearing the 
fruit. The proleptic blossoms had, 
with the relatively scanty nutritive 
supply and the short time granted 
them for development in the fall, 
naturally little opportunity to develop 
the parts of the cortex into well fla- 
vored fruit flesh. This explains, on 
the one hand, the lack of size and, on 
the other, the lack of flavor of the 
pears here described. If the fruit buds 
had not been stimulated by the un- 
usually increased supply of water at 
the then autumnal season, they would probably have yielded perfectly 
normal fruits the following year. 

While the fruit remained seedless in this case, because in the proleptic 
development the accumulated building materials are insufficient, other cases 
also occur in which enough material is present, but is utilized in some other 
way because of the destruction of the normal embryo. Thus Miiller- 
Thurgau^ states that pears whose carpel layers had been destroyed by a late 
frost, produced fruit then exhibiting in place of a core a hollow chamber in 
which tissue excrescences had grown out from the side wall. 

The appearance of seedless fruits is, therefore, to be treated primarily 
as a question of food supply. The organic building substances are not 




Fig. 36. Seedless Pear. 



1 Muller-Thurgau, H., Eigenttimliche Frostschaden an Obstbaumen und Reben. 
X-XII. Jahresb. der Deutsch-schweizer. Versuchsstat. Wadensweil, 1902, p. 66. 



295 

sufficient to nourish the embryo, no matter whether this arises from a fail- 
ure of the stimulus of fertilization, from the poor position of the various 
blossoms, from the exhaustion of the tree as a result of a previous heavy 
crop, or from a proleptic developm.ent of a fruit bud. In consideration of 
the fact that seed-containing fruits develop better than seedless fruits from 
the same tree, it is more advisable agriculturally and horticulturally, as long 
as seedless varieties cannot be cultivated with absolute certainty, to en- 
courage the possibility of seed formation. 

Even if Ewert has proved that although in orchards of one variety 
the number of seedless and poorly seeded fruit is large, the fruits producing 
seeds still predominate, on which account he has asserted that "pure planting" 
is advisable, yet for the present we would give preference to mixed planting. 
The practical disadvantages in regard to the protection and harvesting of 
varieties growing and ripening differently may be decreased by cultivating 
each variety in rows. In avenues of trees at all times that variety which is 
most nearly ripe should be especially watched. 

The Behavior of Weak Seeds. 

The causes, which have affected the failure, or the poor maturing of 
the seeds in seedless fruits, have been felt more or less in other cultivated 
plants, so that we must also consider the behavior of poorly developed seeds. 
The scanty amount of nutriment must manifest itself in the specific gravity 
and, in this connection, Clark's^ experiments show that seeds of low specific 
gravity do not germinate at all while those somewhat heavier germinate 
sparsely and often produce weak plants. The highest 4)ercentage of germi- 
nation is found in seeds with the highest specific gravity. 

According to Hosaeus'- experiments, normal plants can be produced 
even from immature, i. e. specifically light, seeds by carefully providing ver}' 
favorable conditions. But the death rate is considerably larger in compari- 
son with that of normal seeds. This refers especially to the use of grain, 
for example, which had necessarily been harvested in the milk stage. Some- 
times the immature seeds undergo a sufficient subsequent ripening, outside 
of their fruit covering, and can then, under certain circumstances, germi- 
nate more quickly than the incompletely matured ones. According to 
KinzeP this may occur in parasites of silk varieties (Cuscata) and is very 
well worth consideration in combatting them. 

At times, with a poor quality of seed, a careful soaking is beneficial in 
order to shorten as much as possible the time the seed lies in the soil before 
its germination. Immature seeds especially decay much more quickly, par- 
ticularly in heavy soils. But this soaking of the seed is disadvantageous 
because the seed must lie longer in the soil ungerminated if a period of 



1 Clark, A., Seed selection according- to specific gravity. New York Exper. 
Stat. Bull. 256. 1904. 

2 Deutsche Landwirtsch. Presse, 1875, No. 4. 

3 Kinzel, W., L'ber die Keiming- halbreifer und reifer Samen der Gattung Cus- 
cuta. Landwirtsch. Versuchsstat. 1900. Vol. 54, p. 125. 



296 

drought occurs, than if it had been sown naturally. Zawodny^ has proved 
this experimentally for cucumbers. In this connection reference must be 
made to the already discussed interruption of germination by drought. 

Dropping of the Fruit. 

Besides the dropping of pears already mentioned, which Miiller-Thur- 
gau observed as the result of drought at the time of blossoming, fruit-bearing 
trees have an annual house cleaning during which poorly nourished blossoms 
or young fruits are dropped. The flowers developing last at the tips of the 
inflorescences, especially those at the ends of branches, are the ones cast ofif. 
There is not enough plastic nutriment at hand for development. The fruits 
nearest to the source of supply, the trunk axis, take up the nutritive sub- 
stances at the expense of the organs further out. For fruits cultivated on 
trellises, these nutritive relations can be regulated artificiaHy, since a large 
part of the unfavorably placed specimens can be removed with shears soon 
after the fruit is set. 

In growing fruit for market very exact consideration must be given the 
moisture requirement, especially that of peaches and apricots. When the 
stone begins to harden, the most water is needed, and the dropping is often 
caused by a single dr)^ period. Before and after this stage of development, 
however, more care must be used in watering, since otherwise sprouts are 
produced too early, which divert the material necessary for the maturing of 
the fruit. Then, at a later stage, the fruit will drop from a lack of nutri- 
ment, or, at least, be injured by it. 

We have already mentioned in previous chapters that mature fruits 
may drop because of a late dry period, and it is now necessary to recall that 
fruit, injured by a late spring frost, is sometimes found in great quantity 
on the ground. All causes which lead to the sudden lost of function of an 
organ ultimately effect its dropping. 

The Drying of the Inflorescences on Decorative Plants. 

This phenomenon is often met with especially by amateur growers of 
potted plants. Aside from the effect of dry air which will be treated later, 
and the dryness of the soil already mentioned, there are two circumstances 
that come under consideration here. Both represent a starving of the blos- 
som buds. In one case it is actually a lack of nitrogen which manifests it- 
self when the plants stay in the pots too long, in the other case it is a lack 
of food for the blossoming organs, since other organs have taken it. 

Our azaleas and camellias serve as the most usual example of the latter 
case. Plant lovers complain very frequently that the plants which have a 
great many buds do not open their buds in the house. In azaleas the buds 
become dry, in camellias they fall. In both cases fresh, rapidly and vigor- 
ously growing shoots develop prematurely directly under the blossom buds. 



1 Zawodny, J., Keimung der Znaimer Gurke. Cit. Bot. Jahresber. 1901. Part II, 
p. 236. 



297 

In this premature breaking forth of the young branches Hes the cause of the 
"fall of the blossoms." The error in treatment is that the plants are kept 
too warm and moist and insufficiently lighted for the given stage of their 
development. While the flower, to be sure, needs warmth and atmospheric 
humidity for its development, too great moisture in the soil injures it. This 
incites the leaf buds near the blossoms to a premature exfoliation and these 
attract the current of nutritive substances to themselves, squeezing out the 
functionally weak blossom buds. 

In forcing bulbs, especially tulips, we also find such conditions of star- 
vation of a flower bud resulting from too vigorous a development of the 
vegetative organs. In the newer cultivated varieties we often find that the 
flower stalk is not leafless, but has one or two leaves borne on clearly 
marked nodes. In such examples, the bud is so weak that, when forced in 
winter, it cannot develop at all, but dries up, because of preponderating leaf 
growth, resulting from the excess of moisture and warmth. 

An experiment made with V eltheimia glauca may be cited as an ex- 
ample of the drying up of the flower buds, due to a lack of nitrogen. A 
vigorous double bulb had been divided several years previously and each 
daughter bulb had bloomed regularly every winter after this division. When 
later one of the bulbs was not transplanted, while the other was set in new, 
rich earth, the inflorescence developed earlier in the former, to be sure, and 
was more slender, but the flowers dried up before being completely formed. 
This plant was now given hornshavings as a source of nitrogen, without 
changing the soil in the pot. In the following year the inflorescence appear- 
ed to be more vigorous and the flowers more numerous ; part of them de- 
veloped and became colored, but not so deeply as those from the bulb which 
had been transplanted each year. 

It is well known that a supply of nitrogen will increase the product of 
agricultural plants. 

The Formation of Thorns. 

The formation of thorns, i. e., the replacing of a bud on the end of a 
shoot by a woody, pricking tip, may be perceived as an indication of the lack 
of nitrogen. A comparison of figures 37 and 38 (cross-sections of Rhamnus 
cathartica) shows what changes have taken place. The tissues, indicated in 
both figures by the same letters, should be compared. We see that in the 
formation of thorns, the thick-walled elements gain the upper hand, and that 
even the parenchyma cells of the bark and of the pith have unusually thick 
walls. A young branch ending in a thorn, can at times form lateral buds at 
its base, if enough nitrogen is still present for the formation of the meriste- 
matic centers. But these lateral axes begin to assume thorn-like character- 
istics early in their development. Ducts may be found as far along on the 
thorns as leaf buds can be recognized and even for a distance beyond them. 
These usually disappear in the apical region. 

The elimination of thorns is especially desirable horticulturally because, 
for example, the thorns of such plants as Crataegus, Pirus communis, 



298 




Prunus spinosa, etc., are very 
apt to injure people working 
among them. The transfor- 
mation of the thorns into nor- 
mal leafy shoots, ending with 
a terminal bud, results from 
pruning and transplanting the 
wild plants to rich, loose, well 
drained soils. 

c. Changes in Production 

due to a lack of 

Potassium. 

By way of introduction, 
reference must be made once 
more to the fact that a lack 
of potassium in the soil condi- 
tions a lack of moisture. HoU- 
rung's^ recent experiments 
have proved that a soil mixed 
with potassium salts contains 
much more moisture than the 
same soil under otherwise 
similar conditions. 

The potassium enters the 
plant in the form of potassiuia 
nitrate, sulfate and phosphate, 
chlorid or even silicate. In 
the plant it may be found in 
combination with organic and 
inorganic salts and especially 
in the tissues in which carbo- 
hydrates may be .found. Hell- 
riegel andWilfarth proved ex- 
perimentally that the amount 
of carbo-hydrates deposited 
as reserve substances (starch 
and sugar) in potatoes, grain 
and sugar beets, depends 
directly on the amount of 
potassium supplied. Thus 
it is evident that a lack 
of potassium must manifest 



„ - . -r 

Fig-. 37. Cross-section through a one-year old 
branch of Rhamnus cathartica. 



1 HoUrung-, Vortrag im An- 
haltinischen Zweigverein fiir 
Zuckerriibenkultur. Blatter f. 
Zuckerriibenbau 1905 p. 76. 

a Cuticula, h Epidermis, c Cork layer, d 
Phellogen ( cork cambium ) , e Collen- 
chyma./and./"' Bark parenchyma, £■ and ir' 
Bast bundles, h .Secondary bark, / Wood, 
and on its periphery, the cambial zone, 
k Pith, 7)1 pith di.sc. (After Dobner-Nobbe) 



299 



itself in a scarcity of the reserve substances. Besides this, tlie lack of 
potassium explains also the fact, already observed, that shoot formation is 
retarded, since the cellulose, necessary for the formation of the parenchyma, 
is likewise a carbo-hydrate. 

Without potassium, the plant becomes green, to be sure, but does not 
grow much beyond the amount of material furnished from the seed. All 
other nutritive material, therefore, can not have been used (law^ of the 
minimum) . According to Nobbe's 
studies, if the very valuable com- 
pound, potassium chlorid, was 
given to potassium hungry plants, 
even after they had lain dormant 
for months, an increase in growth 
was produced in two or th.vee 
days. The formation of starch 
began immediately \ An addition 
of potassium becomes fully effec- 
tive, however, only when it is not 
rendered inactive by calcium. Ad. 
Meyer- emphasizes the especially 
favorable action of potassium 
chlorid, but he found this con- 
siderably weakened when calcium 
bi-phosphate was also present. 
With sugar beets potassium 
chlorid, as well as calcium chlorid, 
when used alone, worked very 
well, but not if added simul- 
taneously. 

Hellriegel found in grain that 
with a scanty potassium supply, 
the green parts matured at the 
expense of the kernels. This is 
not the case with a lack of nitro- 
gen ; the plants then develop com- ^'^s 
pletely but remain small. In trees 
a continued lack of potassium 
always leads to a weaker develop- 
ment of the end shoots and finally to "tip blight" and Janson'^ states that he 
has cured this disease by a direct addition of 40 per cent, potassium salt. 
Naturally tip blight can be produced by veiy different causes, and on loamy 
soils especially other causes must often be sought primarily. 

i Nobbe, Schroder and Erdmann, Die organische Leistung des Kalium.s in der 
Pflanze. Landwirtsch. Versuchsstat. XIII p. 321. 

2 Jahresber. f. Agrik. Chemie 1880 p. 269. 

3 Janson, A., Kalidiingung- gegen die Spitzendiirre. Prakt. Ratg'. f. Obst- und 
Gartenbau 1905 No. 38. 




38. 



Cross-section through the thorn of 
Rhamnus cathartica. 



Explanation of letters as in Fig. 37. only here the phello- 
gren (d) and secondary bark (A) are lacking. They appear 
transformed into permanent cells. (After Dobner-Nobbe) 



300 

Agriculturally worth consideration is the fact, confirmed experi- 
mentally\ that with a lack of potassium, as contrasted with complete nu- 
trition, a larger part of the nutritive substances taken up (excepting the 
phosphoric acid) will wander back into the soil at the time of ripening. 
This was observed, at least, in summer wheat, barley, peas, and mustard. 
Potatoes formed an exception. 

The manifestation of a lack of potassium in fungi is very interesting. 
Molliard and Coupin- found in Sterigmatocystis nigra a malformation of the 
conidia which were produced only very exceptionally and matured incom- 
pletely. As under other conditions due to starvation, the conidia germi- 
nated at once, but their contents grew into a chlamydospore form. 

The most important question for agriculture is, whether positive ex- 
ternal characteristics may be found which indicate with certainty the lack of 
potassium ? 

We owe the most important experiments along this line to Wilfarth 
and Wimmer^, who set up comparative cultures of sugar beets, potatoes 
buckwheat etc. They tested also for scarcity of nitrogen and phosphoric 
acid and found that with a lack of nitrogen leaves took on a light green 
to yellowish coloration and finally dried up with a light brownish yellow color. 
With a lack of phosphoric acid they were colored a deep, dark green, cor- 
responding to the occasional excess of nitrogen, and in extreme cases black- 
ish brown spots were formed at the edges and later distributed over the 
entire surface of the leaf, which sometimes had a reddish color at first. 
Finally followed a drying up accompanied by a dark green to a blackish 
brown coloration. If, however, sufficient potassium lay at the disposal of 
such starved plants, abundant quantities of starch and sugar were formed 
in spite of this ; even with a lack of nitrogen, this process seems to be in- 
creased rather than decreased. If, however, in an otherwise normal nutri- 
tive supply, the potassium is lacking, the above-mentioned increased forma- 
tion of straw in grain as against the formation of kernels becomes manifest. 
Under these conditions the amount of green growth in edible roots, or 
tuberous plants, was increased in proportion to the containers of the reserve 
substances, which possessed appreciably less carbo-hydrates than with a 
lack of nitrogen and phosphoric acid. 

Since the plants use first of all the potassium supply in building their 
vegetative skeleton, they retain longer, by their habit of growth, the appear- 
ance of normally nourished plants with a lack of potassium than with a 
lack of nitrogen and phosphoric acid, but then the internodes are shortened 
and the leaves curl upward convexly. At first near the leaf edges and then 
later scattered over the whole surface of the leaf, appear yellowish spots 
which rapidly turn brown or often change to white, while the petioles and 



1 Wilfarth, Romer and Wimmer, tJber die Nahrstoffaufnahme der Pflanzen in 
verschiedenen Zeiten ihres Wachstums. cit. Centralbl. f. Agrik.-Chemie 1906 p. 263. 

2 Molliard et Coupin, Sur les formes teratologiques du Sterigmatocystis nigra 
prive de Potassium. Compt. rend. ]903. CXXXVI p. 1659. 

3 Wilfarth, H. W. and Wimmer, G. (Ref.) Die Kennzeichen des Kalimangels 
an den Slattern der Pflanzen. Zeitschr, f, Pflanzenkrankh. 1903 p. 82. 



30I 

veins together with the immediately adjacent tissue remain green. Finally the 
leaves dry up, beginning usually at the edges, with a dark brown color (see 
the adjoining Fig. 39). Flower and fruit formation are scanty. With a lack 
of potassium, not infrequently, individual plants go to pieces prematurely'^, 
while, with a lack of nitrogen and phosphoric acid, even the smallest plants 
can be maintained until the end of the time of growth. 

Of especial importance is the observation of the above-named authors, 
that the roots as well as the tubers of plants grown with a lack of potassium 
tend very easily to decay and that plants lacking any nutritive substance 
are always more predisposed to attack from animal and vegetable parasites. 

Von Feilitzen- made the same observ^ation on timothy grown on moors. 
It was attacked by fungi only after it had been weakened by a lack of potas- 
sium. He noticed in clover that the lots sown without potassium, or with 
a slowly soluble compound of it, were "scorched" as if grown on poor 
sandy soil, after long periods of drought. 

When experimenting with dififerent fertilizers, Moller found that with 
a lack of potassium the seedling plants of the Scotch pine had less growing 
power, their needles had a faded appearance. 

Valuable as are these attempts to find positive characteristics due to a 
lack of potassium, I still think that for a long time we will have to make use 
of these characteristics only with great care in diagnosis. In the first place, 
we do not know whether the same characteristics always, — i. e. with all vari- 
ations of the factors of growth,— become visible in the same species. In the 
second place, we still know too little of the phenomena of starvation which 
make themselves felt with other nutritive substances. In the third place, the 
influence of injurious gases at times gives such deceivingly similar efifects, 
aside from parasitic attacks, that it might be difficult to draw definite con- 
clusions from the changes in habit alone. It should be taken into consider- 
ation that almost all injuries to the leaf manifest themselves first in the 
regions lying farthest away from the veins conducting water, hence the fre- 
quent beginning of the diseased condition at the edge of the leaf or in the 
middle of the intercostal areas, upcurved between the larger veins. 

d. Changes Due to a Lack of Calcium. 

It is well known that the plant uses calcium as stiffening for the cell 
walls and as a means for combining the poisonous oxalic acid produced. 
In the phenomena of disease, the fact that an excess of oxalic acid can re- 
dissolve small amounts of calcium oxalate is important^. The calcium oxa- 
late produced is re-dissolved only in a few cases*. Usually the organism 



1 Compare also, v. Seelhorst, Die durch Kalimangel bei Vietsbohnen (Phaseolus 
vulgaris nanus) hervorKerufenen Erscheinung-en. Zeitschr. f. Pflanzenkr. 1906. p. 2. 

2 V. Feilitzen-Jonkoping-, Wie zeigt sich der Kalimangel bei Klee und Timothee- 
gras? Mitt. d. Ver. z. Ford d. Moorkultur 1904. No. 4. p. 41. 

3 Wiirtz, Dictionaire de chimie II, p. 647, cit. bv de Vries in Landwirtsch. Jahrb. 
1881 p. 81. 

4 Sorauer, P., Bertrag-e zur Keimungsgeschichte der Kartoffelknolle. Berlin. 
Weigandt & Hempel. 1868, p. 27, and de Vries, H., tjber die Bedeutung der Kalkab- 
lagerungen in den Pflanzen. Landwirtsch. Jahrb. v. Thiel, 1881, p. 80. 



302 




Lack of potassium. 



1. Deformed tobacco leaf, resultingr from a lack of potassium, with partially split, brown edges: only the 
venis are still green while the intercostal fields appear discolored vellow to white; 2, Leaf of a normally 
nourished potato plant: 3, that of one starving for potassium. In this the leaflets stand closer to one another 
and are curled under. The places drawn in light are yellowish, the intercostal fields are flecked with 
brown, as also the edges of the leaves: 4 and 5, leaves of the buckwheat plant with spots which are yellow- 
ish, then brown, and finally white. (After Wii.farth and Wimmer). 



303 

does not possess the ability of re-dissolving the calcium already deposited in 
old tissues in appreciable amounts and transporting it where it can instantly 
become effective for new structures, when there is a lack of calcium. At 
least the experiments of Bohm^, Raumer and Kellermann- and Benecke'' 
prove that no calcium, or ver}' little passes from the containers of reserve 
substances into the young tissues when the plants are grown in distilled 
water, in solutions free from calcium, or in quartz sand. The fact that no 
calcium is necessary for the formation of starch itself has been proved by 
Bohm. He found that primordial leaves free from starch with shrivelled 
petioles became filled with starch when grown without lime, but under 
otherwise favorable conditions. In order to dissolve the reserve substance 
and to transport it chemical combination with calcium is necessary, for an 
investigation of plants grown in media lacking calcium proved that the 
organs (leaves, cotyledons) had not given up all the starch, the leaf body 
or the adjacent internodes retained considerable quantities, while the young 
plant starved to death despite its sugar content. My own experiments* also 
led to the conclusion that the plant needs neiv mineral substances originating 
from the solution in the soil, even at a time when it is working up the re- 
serve material into cellulose, etc. 

Thus in the germination of seeds an addition of calcium acts bene- 
ficially; in fact, it often seems necessary. The statement that calcium is 
disadvantageous for germinating seed^ may have arisen from a use of too 
highly concentrated solutions. Loew and May declare that definite excess 
of calcium in the soil over the magnesium content can produce starvation 
symptoms in the plant (see Lack of Magnesium). An earlier assertion of 
Deherain and Breal" that, with a lack of calcium the plants can better 
utiUze the lime stored in their bodies, if the temperature is raised, has 
not held". Molisch, as well as Portheim, has also proved the error of these 
statements^. 

Among the older observers'*, Nobbe describes the phenomena due to a 
lack of calcium in water cultures. Buckwheat, peas, Robinia, etc., grew but 
little beyond the germinating stage. The pale leaves exhibited spots, simi- 
lar to those produced by the action of acid, which dried up gradually, and 
then the petioles often broke. On conifers, the tips of the first year needles 
became yellow to brown. 



1 Bohm, tJber den veg-etabilischen Niihrwert der Kalksalze. Sitzungsber, d. k. 
Akad. d. Wissensch., Vol. 71, 1875, p. 287 ff. 

2 V. Raumer and Kellermann, tJber die Funktion des Kalks im Leben der 
Pflanze, I^andwlrtsch. Versuchsstationen XXV, 1880, Parts 1 and 2. 

3 Benecke, W., tJber Oxalsaurebildung- in grunen Pflanzen. Bot. Zeit. 1903, Part 5. 

4 Sorauer, Studien iiber Verdunstung-. Forsch. auf d. Geibiete d. Agrikultur- 
Fhysik, 1880, p. 429. 

5 ■\V''indisch, R., tJber die Einwirkung de.s Kalkhydrates auf die Keimung. 
Landwirtseh. Versuchsstationen. 1900, p. 283. 

6 Annales a.gronomiques, Vol. IX, 1883, No. 52. 

7 Kriiger, W.. und Schneidewind, W., Zersetzungen und Umsetzungen von Stick- 
stoffverbildungen im Boden durch niedere Organismen, etc. Landwirtseh Jahr- 
biicher, 1901, p. 633ff. 

8 V. Portheim, L.., tJber die Notwendigkeit des Kalkes fiir Keimlinge. etc. 
Cit. Bot. Jahresber. 1901, Section II, p. 141. 

» Dobner-Nobbe, Botanik fiir Forstmanner. 1882, p. 314. 



304 

Recent cultural experiments with grain, buckwheat and Elodca cana- 
densis'^ in nutrient solutions, free from calcium, showed that after a five day 
retention in a solution free from calcium, the root growth became less and 
later ceased entirely. The roots turned brown and the root cap died. Pe- 
culiar, brownish spots were found on the leaves, which soon went to pieces. 
The content in acid potassium oxalate and in starch was greater than in 
normal plants. The death of plants, in a nutrient solution without calcium, 
has been traced by Loew to a poisonous action of the magnesium salt. 
Bruch's cultural experiments with magnesium sulfate, nitrate, carbonate, 
and phosphate in aqueous solutions showed that the roots, to be sure, soon 
stopped growing, but the aerial parts developed further perfectly normally 
and even blossomed. Wheat plants in solutions free from calcium and 
magnesium died far more quickly than those in solutions lacking only the 
calcium. 

Amar- observed the absence of calcium oxalate crystals in those leaves 
which were formed after the plants had been put in a solution free from 
calcium. 

A further insight into the conditions due to a lack of calcium is given 
by Kriiger and Schneidewind through Schimper's statement that, when the 
calcium is removed, all the symptoms of poisoning from an enormously large 
content of acid potassium oxalate are indicated. In Phaseolus these authors, 
to be sure, could prove no especial increase of a strong organic acid. They 
succeeded, however, in keeping the plants until all the reserve substances 
had been used up by painting dying seedlings with a calcium solution either 
on the hypocotyles or at the place where death usually begins. This sub- 
stantiates Bohm's observations that seedlings of the scarlet-runner bean 
take up calcium as well as water through the outer skin of the petioles and 
leaves. 

The experiments of Moisescu^ confirm the above observations. He 
found in different cultures in nutrient solutions that those seedlings had be- 
came affected earliest and most extensively which had grown in solutions free 
from calcium. In Platanus orientalis, the leaves of which partially became 
brown and dry along the veins, it was found that the diseased ones contained 
twice as much acid as the healthy ones. Glocosporiiim nervisequum in- 
fested the diseased leaves. On this account it must be assumed that the 
parasite named attacks only weakened leaves. This weakness would con- 
sist here of "Calcipenuria," that is to say, a lack of calcium. In the author's 
opinion, not enough calcium was present to convert the excessive potassium 
oxalate into calcium oxalate. 

Besides cultural experiments of this nature, a large number of practi- 
cal results point to the injuriousness of calcium poverty. At least we find 
in many cases a cessation of the phenomena of disease after an addition of 

1 Bruch, P., Zur physiologischen Bedeutung des Calciums in der Pflanze. 
Landwirtsch. .lahrb. 1901. Suppl. III. p. 127. 

2 Amar, Maxime, Sur le role de I'oxalate de calcium dans la nutrition des 
veg-etaux. Annal. sc. nat. bot. 1904. XIX, p. 195. 

3 Moisescu, N., Ein Fall von Calcipenuria, Zeitschr. f, Pflanzenkr. 1905, p. 21. 



305 

calcium. In this, the calcium may often act beneficially on the constitution 
of the soil and often directly on the composition of the cell sap. According 
to our explanation of the matter, a considerable number of cases of disease 
exist which are called forth directly by nitrogen excess, and for which the ad- 
dition of calcium and phosphoric acid remains the only efifective remedy. 
In the division "Enzymatic Diseases," we will also have to consider the 
beneficial action of calcium fertilization. There we will also touch upon 
the subject of the over-abundant formation of acid in the plant which cer- 
tainly sometimes influences unfavorably the mode of production. Thus, 
for example, with a lack of calcium in the soil, the sap of sugar cane con- 
tains a great deal of acid and but little sugar\ We will mention later special 
cases of oxalic acid poisoning. 

e. Changes Due to a Lack of Magnesium. 

Plants grown in a nutrient solution lacking magnesium often live longer 
than when the nutrient solution does not contain calcium. It might be con- 
cluded from this that the plant is able more easily to remobilize the mag- 
nesium compounds already deposited in its tissues and to make them partially 
accessible again for the young organs. If the grain becomes diseased slowly 
from magnesium hunger, the leaves are a light green and appear limp, but 
not directly wilted. From the beginning it is possible to imagine a very 
considerable effect on the formation of seeds, if one considers that, for ex- 
ample, the globoids enclosed in the protein grains may be assumed to be 
calcium and magnesium compounds of. a double phosphoric acid. In 
reality, with a lack of magnesium, there is a decrease in the formation of 
fruit, as stated by Nobbe-. He gives the following symptoms. The leaves 
become pale in color, with yellow to orange red spots here and there. 
The chlorophyll grains are pale yellow green and contain, as a rule, small 
amounts of starch. Diminished cell division is noticeable in the epidermis. 
Nobbe found that plants grown with a lack of magnesium correspond to 
those from nutrient solutions free from nitrogen, in that red spots are 
present on the petioles and the leaves fall prematurely. The latter character- 
istic may well be present in all stained plants, since the young organs ex- 
haust the older ones when the supply of nutriment is insufficient. 

Moller^ also observed an orange red coloring in his cultivations of 
Scotch pine seedlings with a lack of magnesium. He says that the needles 
in October had bright orange yellow tips but farther back passed through 
a bright red zone into a normal green one. The discoloration appeared 
when the seedlings had been given magnesium in the second year. 
Ramann analyzed the orange tipped needles of two-year old Scotch pines 
and found that these contained 0.2791 per cent, magnesium (calculated on 
the dry weight), while the adjacent normally green specimens showed a 
content of 0.6069 P^^" cent. 

1 Semler, Tropische Agrikultur. II Edition. Vol. Ill, p. 236. 

'- Dcibner's Botanik fiir Forstmanner, edited by Nobbe. 4th Edition, p. 315. 

3 Moller, A., Karenzerscheinungen bei der Kiefer. Sond. Z. f. Forst- und Jagd- 

wesen, 1904, p. 745. 



3o6 

In regard to the action of magnesia, Loew and May^ have expressed 
the opinion that a definite quantitative proportion between soluble calcium 
and magnesium compounds is necessary for favorable growth (corres- 
ponding approximately to their molecular weights, i. e. 5 to 4). Magnesium 
in the soil in great excess over calcium is injurious. Plants which in so far 
lack magnesium, as that calcium is present in excess, exhibit symptoms 
of starvation. A small excess of calcium arrests the poisonous action of the 
magnesium. In the use of fertilizers containing magnesium, calcium should 
also be given at the same time. This advice should be taken to heart. Even 
if plants can well endure magnesium, and even actually need it, any excess is 
certainly injurious, as has also often been proved in fertilization with raw 
potassium salts. 

f. Changes Due to a Lack of Chlorine. 

It should perhaps be assumed that chlorine and calcium are antagonistic 
in plants. Mayer's conclusion, mentioned under potassium, that the action 
of potassium chlorid is weakened by calcium and, conversely, would indicate 
this. In the same way Knop- found that less calcium is taken up when the 
nutrient solution contains chlorine, and the calcium did not appear to be 
represented in any corresponding way by potassium or any other base. Thus 
the chlorine compounds (by the retention of the calcium) cause an essential 
increase in the acid content of the plant sap. Since, among the acids ab- 
sorbed, the phosphoric acid predominates, Knop thinks it permissible to 
ascribe to this acid the greater fertility with a use of nutrient solutions con- 
taining chlorine, which was observed bv Nobbe. Accordingly one would 
like to explain the process thus, — the chlorine which accumulates" in greatly 
different quantities in the plant body, according to the amounts offered the 
roots, can increase the transportability of the phosphoric acid, since it 
decreases the absorption of calcium and thus prevents the appearance of the 
phosphoric acid in the slowly soluble form of calcium phosphate. If the 
phosphoric acid, co-operating in the formation of the proteins, reaches 
very easily the meristematic areas of the growing tips, an abundant forma- 
tion of cytoplasm occurs together with cell increase and, in connection with 
this, a plenteous streaming of the carbo-hydrates for the protein regenera- 
tion. Accordingly, vigorously growing shoots with but little stored up reserve 
substances will necessarily be found in plants, fertilized with chlorine. 
Actually, the many fertilization experiments show a decrease in starch and 
reserve sugar in the luxuriantly growing cultivated plants. 



1 Loew, O., and May, W., The relation of lime and magnesia to plant growth. 
U. S. Department of Asric. Bull. I. cit. Bot. Jahrestaer. 19'>1. II p. 141. 

2 Chemisch-physiologiscne Untersurhungren iiber die Ernahrunsr der Pflanze 
von Knop and Dworzak. Aus Berichte d. Kgl. sachs. Gesellsch. d. Wissensch. vom 
23. April, 1875. Cit. Jahresber. f. Agril^ulturchemie, 1875. p. 267. 

^ Pag^noul, Sur le role exerce par les sels alcalin sur la veg-^tation de la b^'tter- 
ave et de la pomme de terra. Compt. Rend. 1875. Vol. LXXX, p. 1010. Fertilizing- 
experiments carried on for five years with chlorids showed for beets a fluctuation in 
contents from 1 to 50. In potatoes, the smallest yield in tubers coincided with the 
least amount of potassium carbonate in the ash but with the greatest amount of 
chlorides. 



307 



kAT 




Fi£ 



40. Blossoming buckwheat plant grown in a normal 
nutrient solution. (After Nobbe.) 



Besides the probable increase in 
the transportability of the phos- 
phoric acid, it can be proved that 
chlorine has a favorable influence 
on the transference of the starch 
prepared in the leaves. According 
to Nobbe's experiments, the plant 
starving for chlorine continues to 
grow, exhibits a very dark green 
color and gives a considerable pro- 
duction of substances rich in carbo- 
hydrates, but sooner or later,^ — at 
any rate before the time of blos- 
soming, — there occurs a peculiar 
change in form and structure. 
Nobbe found the dark, abnormally 
fleshy leaves crammed full of 
starch (in oak and buckwheat) 
rolling up, becoming brittle and 
dropping. The stems and petioles 
seem puffed up, the intemodes of 
the stems always are shorter and 
many finally dry from the tips 
backward. If the plant reaches 
the blossoming stage, only scat- 
tered, unusually poor small fruits 
develop, despite the abundant 
starch material in the leaves. The 
effect of a lack of chlorine is best 
recognized by a comparison of a 
normal buckwheat plant with one 
grown with a 
lack of chlorine 
(figures 40 and 
41). 

g. Lack of Iron 
AND "Jaun- 
dice" (Icter- 
us). 

The expres- 
s i o n s, "jaun- 
dice," "yelloiv- 
sickness, "white- 
l e a V e d n ess," 
"v art egation," 



3o8 



(b) 



"chlorosis," "alhication," "etiolation," are the most common names for the 
condition in which a leaf loses its green coloring matter in spots, or over 
the whole extent of its surface. The causes for this change in color are 
very different, but always represent a condition of weakness. 

In order to survey the manifold causes of the disease, we will endeavor 
to group them into 

I. Induced and non-transmissible conditions. 

(a). The discoloration attacks the whole surface of the leaf, 
which has matured in the light. After having been green 
in its young stages, the whole leaf assumes a yellowish, 

yellow to yellow- 
white color tone. 
Icterus or jaun- 
dice. Cause : usu- 
ally a lack of nu- 
tritive substances. 
The pale discol- 
oration is present 
in the young organ 
and the leaves re- 
main in a con- 
dition resembling 
youth until their 
p r e m a t ure end. 
Cause : lack of 
light and at times 
of heat (see these 
topics). 
Innate and transmis- 
sible conditions. 
Portions of the 
plant show yellow 
to pure white spots or stripes. Those plants suft'er especially in 
which pure white leaves appear near the ones spotted with green 
or all green. The spots have usually a sharp demarcation. 
White-leavedness, alhication, variegation, sometimes transmissible 
through seeds or by grafting. Cause : probably enzymatic dis- 
turbances (see these). 
Of course there are intermediate stages between the types named, since 
the individual causes often work together. ' 

In the present division we will examine only the icteric conditions and 
treat them under lack of iron because, since the investigations of the Gria\ 
father and son, it is customary to consider jaundice as caused especially by 




2. 



Fif 



41. Buckwheat plant grown in a solution 
free from chlorine. (After Nobbe.) 



1 Gris, A., Ann. scienc. nat., 1875, VI ser. Vol. VII. p. 201. 



309 

a lack of iron. The authors named found jaundiced leaves turning green 
where painted with a soluble iron salt. A change to green may also be ob- 
served if the roots of such plants have a dilute iron solution at their disposal. 
The experiments on the efifectiveness of the iron solution were often re- 
peated; as, for example, by Knop^ and Sachs-, who observed in cultures of 
maize in nutrient solutions free from iron, that the plants remained green 
only as long as the reserve material from the seeds lasted. After this time, 
leaves developed which were green only at the tip and were already yellow 
at the base, until the next leaves appeared uniformly icteric. Similar dis- 
colorations, at first appearing in stripes, were found on mature plants which 
had developed normally at first, and then were placed in a nutrient solution 
free from iron. The blossoms then became sterile and the production in dry 
weight was considerably less. Frank^ observed that there occurred with a 
lack of iron an universally noticeable phenomenon of starvation, viz., the 
newly produced leaves exhausted the older ones, which lost their color and 
died. In icteric organs, the chlorophyll grains have a normal form, but their 
number and size is possibly smaller and their color pale. Although the 
chlorophyll pigment contains no iron*, the whole nutritive condition of the 
chlorophyll grain will become weakened by the lack of iron. But at first 
the chloroplast exists in a normal form which is not destroyed until later. In 
this lies the difference between the phenomena of starvation and enzymatic 
albication. 

In order not to be obliged to separate the phenomena whose similar 
symptoms lead to confusion, we will mention here icterus due to cold. We 
find in cold, wet seasons a gradual yellowing in most cultivated plants, which 
disappears of itself with a rise in temperature. Often in spring, the leaf 
points of our flowering bulbs are yellow when they push out of the earth 
and the young leaves push out gradually with a normal green color only as 
the weather becomes warmer. 

From this transitory jaundice must be distinguished the chronic form, 
in which the yellow leaves always remain yellow. This may be observed if 
sudden great cold affects the young cells and destroys the chloroplasts. 
Then, in place of these, are found only fine grained yellowish groups and 
at times also yellow drops. These cells do not recover later. At the place 
of transition to the parts of the leaves which, protected by the earth, have 
become green, colorless, swollen and also light green chlorophyll grains 
which later partly turn green may be found at the place of transition to the 
portions of the leaf, which, protected by the earth, have become green. 



1 Knop (Jahresberichte f. Agriculturchemie, 1868-69, p. 288) obsei-\'ed in such 
experiments that the iron whicli got into the plant could not be proved in the cell 
sap, and, therefore, must be present in a combined form. In 1860 (Bot. Z. p. 357), 
Weiss and Wiesner determined that iron occurs only in insoluble compounds and 
in the contents of the older cells as well as in their walls. 

2 Experimentalphysiolog-ie, p. 144. 

3 Krankheiten der Pflanzen. 1895, I, p. 290. 

■* Molisch, Die Pflanzen in ihren Beziehungen zum Disen. 1892, p. 81. 



3TO 

With the action of sudden cold, lasting for several hours, Haberlandt^ 
found that a noticeable change occurred at a temperature of minus 4 to 6 
degrees C. and only at minus 12 to 15 degrees C. does the destruction of the 
chlorophyll grains become complete (with the exception of those in ever- 
green plants). With the formation of vacuoles there was produced a dis- 
tortion of the form of the chloroplasts which were either passing over into 
the position along the side walls (apostrophe) or were rolled up in lumps. 
Of these the ones inclosing starch grains were destroyed more quickly than 
those without starch. In the leaves of Vicia odorata no difference could be 
perceived in the destruction of the chlorophyll, dependant upon the age of 
the leaf. 

We will touch upon this subject again under autumn coloring. A 
yellow leaved condition in spring is found often in pears growing in nurse- 
ries, as the after efifect of frost disturbances. 

The grape is very susceptible to icteris. Different factors have been 
recognized here as the cause. In the cases observed by Mach and Kiirmann- 
in the Tyrolean vineyards, the analyses of green and icteric vines, growing 
close together, showed: 

Water Content of the yellow leaves 77.97 per cent. 

Water Content of the green leaves 73.17 per cent. 

Based on dry weight, the green leaves possessed a higher percentage of 
organic substances and of nitrogen, but considerably less ash. The ash of 
the yellow leaves contained six times as much of the elements insoluble in 
hydrochloric acid as did that of the green leaves. On the other hand, there 
was less potassium in the former. Watering with liquid stable manure 
acted beneficially. A similar case is described by E. Schultz'\ The leaves 
and woody portion of the diseased vines contained only half as much potas- 
sium as those of the healthy plants, which were found, however, to be 
poorer in calcium and magnesium. Besides this icterus due to a lack of 
potassium, a jaundice of the grape, resulting from an excess of calcium, has 
been determined by numerous observations. It seems to me that the amount 
of calcium in itself is not the injurious factor, but chiefly the lack of potas- 
sium, since calcium soils, as a rule, are poor in potassium. We will return 
to this case in the section on the excess of calcium. 

Nitrogen starvation is also a frequent cause. This, differing from the 
phenomena due to a lack of other nutritive substances, does not manifeiit 
itself in the death of the plant in an early stage but only retards the growth 
and reduces all the organs to a minimum. 

The oft repeated experiments with the cultivation of non-leguminous 
plants in nutrient mixtures without the addition of nitrogen have shown 
that under otherwise favorable conditions, with certain races, a new min- 



1 Haberlandt, tJber den Einfluss des Frostes auf die Chlorophyllkorner. Osterr. 
Bot. Zeit. Cit. Jahresbericht, 1876, p. 718. 

2 Biedermann's Centralbl. 1877, p. 58. 

3 Zeitschr. d. landwirtsch. Centralver. fiir das Grossherzog-tum Hessen. cit. 
Centralbl. f. Agrikulturchem. 1872, p. 99. 



311 

iature plant can be produced from a seed, developing even to the production 
of a few blossoms and new seeds. The entire nitrogen content of the whole 
plant, however, does not in this case equal that of the original seed. It is 
evident from this fact, firstly, that the plant is not in a condition to make 
use through its leaves of the nitrogen from the air in quantities worth 
mentioning; secondly, however, we perceive that nitrogenous substance 
stored up in the seed enables various individuals to run through their whole 
developmental cycles, that is to say, to perform all the life-processes, in a 
minimum compass. This demonstrates further that the nitrogen stored in 
the seeds is easily mobilizable and capable of transportation, indeed, that the 
same molecule may probably be utilized more than once for the same pur- 
pose in the construction of the cell cytoplasm. A consideration of the 
growth of plants, with a lack of nitrogen, indicates such a condition, for it 
is found that the lowermost leaves are exhausted to the amount of growth 
of the tip of the stem and begin to dry, beginning at the edge, or at the tip. 

In the rapid convertibility and capacity for transportation of the nitro- 
gen a lack of this nutritive substance occurs very rapidly and manifests 
itself in jaundice. In our cultures such cases can also occur, if the supply 
of nitrogen in the soil is still abundant but not in a form available for the 
special requirements of the definite plant under cultivation. The best ex- 
ample is found in our sugar beets, to which, besides stable manure, nitrogen 
is given chiefly in the form of Chile saltpetre. The frequent, very favor- 
able results of fertilizing various other cultivated plants with ammonium 
sulfate have now led to the use of this fertilizer in beet culture. But in a 
practical way these results have not been satisfactory, since the polarization 
of the beets was far from normal. 

In a thorough discussion of this point Hollrung^ Kriiger and Schneide- 
wind emphasize that the sugar beet is a pronounced nitrate plant, but since 
the ammonia is not converted so rapidly and directly to nitric acid by the 
micro-organisms of the soil, a lack of nitrogen compounds may occur and 
the beets suffer although enough nitrogen is present as ammonia. The phe- 
nomena of a yellow leaved condition may be due to the constitution of 
the nitrogen fertilizer which is unsuited to beets, although it may be suit- 
able for grain and potatoes. 

An older note has already pointed to the difference in effect secured 
according to the form of nitrogen provided. Analyses by Lagrauge- showed 
that in beets fertilized with ammonium sulfate, twice as great an ammonia 
content was demonstrable as in those fertilized with sodium nitrate. 

It is a well-known fact that a yellow color can be caused in beet leaves 
by drought alone, so that we need to cite only a very characteristic example. 
In 1896 (according to Troude^), the beets in France, especially in the 
northern part, suffered extensively from a yellow leaved condition. The 

1 Hollrung, Inwieweit ist eine Diingung- mit schwefelsaurem Ammoniak geeig- 
net, bei den Zuckerriiben eine Schadigung hervorzurufen? Vortrag. Blatter fiir 
Zuckerriibenbau, 1906, p. 70. 

^ Biedermann's Centralbl. 1876. I, p. 258. 

3 Cit. Zeitschr. f. Pflanzenkrankh. 1897, p. 55. 



312 

phenomenon appeared in June after a longer period of intense drought and 
became widespread especially in sunny positions and on light soils, while 
regions with a damp, sea climate showed the disease only slightly. The sugar 
content of the slowly growing beet was from 2 to 3 per cent, less than that 
of healthy specimens. 

By a survey of the individual cases just cited, we are led to the con- 
viction that icterus is one of the most widespread symptoms of disturbed 
assimilation. No conclusion as to any definite cause has been furnished as 
yet, however, in the occurrence of jaundice. 

h. Changes Due to a Lack of Phosphorus and Sulfur. 

The distribution of phosphorus in the various parts of the plant, de- 
termined earlier by Ritthausen's macro-chemical studies, was proved later 
micro-chemically by Lilienfeld and Monti, as well as by Pollacci\ The 
last found that, in general, the cell walls are free from phosphorus while 
the proptoplasm, and especially the nucleus, with the chromatin bodies, con- 
tain this element in abundance. Among the aleurone bodies the crystalloides 
and globoids likewise contain phosphorus. The proteins depend especially 
on the amount of phosphoric acid at hand and a lack of it will make itself 
felt especially in the blossom buds and in the maturing of the seed. Accord- 
ing to Nobbe's cultural experiments-, phosphorus does not seem to play any 
part. in the formation of the chlorophyll pigment; — the foliage of oaks which 
had stood for three years in nutrient solutions, free from phosphoric acid, 
was still green. In other plants Nobbe ultimately observed that a deep 
orange red color appears in the leaves and petioles. There is no production 
of any new dry substance, or only a small amount. Moller' observed in 
die needles of his pine seedlings a blue-red- (dull violet) color due to a lack 
of phosphoric acid. In two-year old plants the violet color tended more to 
olive brown. 

In the reports on discoloration phenomena, which set in with a lack of 
various nutritive substances, the results obtained with one plant species 
cannot be applied to a different species, since discoloration is not every- 
where the same. In regard to phosphoric acid, I found that when plants of 
beets, peas, and seradella were grown without phosphoric acid they dried a 
gray green when they had previously been a faded green, but not yellow, 
while, with a lack of nitrogen, the same species turned a pure quince yellow. 

Nobbe found a somewhat better development with a lack of sulfur in 
the nutrient solution, yet his experimental plants scarcely attained half the 
normal height and the yellowish green leaf blades exhibited a correspond- 
ingly scanty development. The starch was scanty and small grained. Cell 
division was considerably impaired. The forming of fruit either did not 
take place, or only very scantily. 



1 Pollacci, G., Sulla distribuzione del fosforo nei tessuti vegetal!. Malpighia. 
Vol. VIII. Cit. Zeitschr. f. Pflanzenkrankh. 1895, p. 299. 

2 Dobner-Nobbe, Botanik fur Forstmanner. 4th Ed., p. 317. 

3 Karenzerschelnung-en etc. Zeitschr. f. Forst- u. Jagdwesen, 1904, p. 7 45 



313 

i. Changes Due to a Lack of Oxygen. 

General Phenomena. 

It is to be assumed as well known that, with the cessation of the supply 
of oxygen, the protoplasmic currents gradually come to a standstill (oxygen 
rigor.) Kiihne^ observed that in an atmosphere of hydrogen the motion in 
the stamen hairs of Tradescantia virginica stopped after 15 to 20 minutes. 
Wortmann- found that the parts of plants in air free from oxygen respired 
at first exactly as much carbon-dioxid as those with an unimpaired supply. 
Later a difference made itself felt in favor of the latter plants. Like the 
gradual cessation of the cytoplasmic currents, this gradual retrogression in 
the amount of carbon-dioxid with the exclusion of oxygen (intramolecular 
respiration) indicates that the oxygen stored in the plant body is consumed 
at first. Death from suffocation, therefore, takes place slowly, especially 
since the green plant with sufficient illumination still decomposes carbon- 
dioxid and water and thus forms oxygen for some time. Bohm^ detected a 
small amount of oxygen in the volume of gas evolved when he enclosed the 
green leaves of land plants in an atmosphere of hydrogen with sufficient 
illumination. 

Aside from the cases which have been observed already in the divisions 
on "Loamy soils" and "Too deep planting of trees," we will consider a few 
occurrences of bad aeration as a result of closing the lumina of the ducts 
forming the main water system. Such stoppage is especially serious for the 
sap wood*. With Bohm^ we may picture to ourselves the process of aera- 
tion as follows : There is not only a difference in pressure between the 
outer air and the diluted air inside the ducts, but also a difference in con- 
stituents. The enclosed air will give up its oxygen in the respiratory pro- 
cesses more rapidly and take up the carbon-dioxid produced. This is either 
soaked up, by the filling of the ducts with water, and carried off in the rising 
sap current, or, since it penetrates the moist walls rather easily, is given out 
in a radial direction by diffusion. The new and necessary oxygen which -n 
lesser amounts may also enter through the roots with the air rich in oxygen, 
dissolved in the water, will, nevertheless, under normal conditions get into 
the plant mainly through transverse conduction. It diffuses more easily 
through moist walls than does the nitrogen of the air, because water absorbs 
it more abundantly than it does nitrogen. Since now the oxygen within the 
plant body is utilized most but is also most easily capable of moving from 
part to part, there results a prevailing dift'usion stream of oxygen from with- 
out inwards in each horizontal plane of a trunk. 



1 Untersuchungen iiber das Protoplasma. 1864, p. 89 and p. 106. 

2 Wortmann, tJber die Beziehungen der intramolekularen zur normalen At- 
mung. Inauguraldissertation, Wiirzburg, 1879. 

3 Bohm, tJber di3 Respiration von Landpflanzen. Sitzungsber. d. Kais. Al^ad. d. 
Wissensch. in Wien, Vol. 67 (1873). 

4 Elfving, tJber die Wasserleitung im Holze. Bot. Z. 1882, No. 42. 

5 Bohm, J., tJber die Zusammensetzung der in den Zellen und Gefafsen des 
Holzes enthaltenen Luft. Landwirtsch. Versuchsstationen Vol. XXI, p. 373. 



314 

Wiesner^ made further observations on gas exchange. He shows that 
the periderm, the cork covering, is completely impermeable to air even with 
great differences in pressure. The exchange takes place only through the 
lenticels which are permeable even in winter. In wood free from ducts the 
equalization takes place through the cell walls, especially through the deli- 
cate pitted walls in which, besides the diffusion, absorption through the col- 
loidal walls comes into effect. In woody bodies, rich in ducts, transpiration 
and the penetration of gases through the ducts, functioning as capillary 
tubes, should also be taken into consideration. The equalization of the 
pressure takes place more quickly axially than transversely. The more 
turgid a parenchyma or wood cell is, the more slowly does the equalization 
of the pressure occur. This relation is reversed in the periderm cell. If it 
incurs the loss of its aqueous contents and is filled with air, whereby its wall 
becomes dry, the cell loses its permeability for gases. In parenchyma 
which conducts air, a part of the air flows through the intercellular passages 
during the equalization of the pressure, another part passes through the 
closed membranes and, indeed, most easily through the places which have 
remained unthickened. 

A statement by Mangin- throws light on the processes taking place in 
trees, with poor soil aeration. He found that the ducts in Ailanthus were 
filled with tyloses, and, in explaining the process, states that, correlative with 
a lack of air in the soil, a deficiency in the supply of air in the ducts takes 
place. Consequently the air in the ducts becomes diluted beyond the opti- 
mum and the tyloses of the adjacent cells push into the tube of the duct and, 
on their part, also hinder the conducting of water. 

In regard to the influence of a lack of oxygen on seeds, Bert's" investi- 
gations should be considered first of all, according to which germination 
progresses more slowly in a lesser air pressure. Many years ago Corti* 
observed that a dilution of the air had an arresting influence on the cyto- 
plasmic currents. Since, however, with a normal air pressure and only de- 
creased oxygen content, germination takes place more slowly and, con- 
versely, with a lowered air pressure but increased supply of oxygen the 
seeds germinate more rapidly, it is evident that even the partial pressure of 
the oxygen alone is a decisive factor. 

In the phenomena due to lack of oxygen, opportunity is again offered 
of pointing to the fact that sudden changes are more disturbing than gradual 
changes. Stich^ found that in an atmosphere poor in oxygen the normal 
respiratory quotient is recovered by decreasing the absolute amounts of oxy- 



1 Wiesner, Versuch iiber den Ausgleich des Gasdruckes in den Geweben der 
Pflanzen. Sitz. d. Kais. Akad. d. Wissensch. zu Wien am 17 April, cit. in Oesterr. 
Bot. Zeit. 1879, p. 202. 

2 Mangin, Influence de la rarefaction produite dans la tige sur la formation 
des thylles gommeuses. Compt. rend, 1901, II, p. 305. 

3 Bert, Recherches experimentales sur I'influence que les changements dans la 
pression barometrique exercent sur les phenomenes de la vie. Compt. rend LXXVI 
et LXXVII. 

4 Meyen, Pflanzenphysiologie, 1838, II, p. 224. 

5 Stich, C, Die Atmung der Pflanzen bei verminderter Sauerstoffspannung 
und bei Verletzungen. Flora, 1891, p. 1. 



315 

gen and carbon-dioxid. With a gradual removal of oxygen, intramolecular 
respiration is aroused only with a considerably lower percentage of oxygen, 
than it is when the oxygen is suddenly decreased. 

The discovery that phenomena of suffocation occur also in seeds if their 
tissue is entirely filled with water is of great value to the practical worker. 
Usually when seeds are soaked they get the water necessary for germination 
'vithout having all the air pressed out of the intercellular spaces. If, how- 
ever, the seeds are kept too long in water, decomposition sets in, in which 
often a distinct ordor of butyric acid, a result of bacterial decay, becomes 
very evident. In the same way experiments, like those of Just^, for example, 
show that when air has been removed by a pump from the tissues ordinarily 
containing air and the space filled with water, the percentage of germi- 
nation is very greatly reduced. 

When seeds have been put in layers on top of each other while damp, 
it is not the excess of water, which so quickly destroys the germinating 
power, but the excessive heating and formation of carbon-dioxid. Wiesner- 
found also that the carbon-dioxid is developed later than the heat. Hence 
its development is not the only source of heat ; this is to be sought also 
in the absorption of wat-er. The seed, coming in contact with water, con- 
denses it as it enters the tissues and thereby frees heat. 

That an excess of oxygen is just as injurious as a lack of it, is natural. 
Bert found that the oxidizing processes in plants are arrested by too high a 
tension of the oxygen. A mimosa died at 6 atmospheres in common air, hav- 
ing lost its irritability because of a lack of oxygen. If the air was made 
richer in oxygen, a pressure of 2 atmospheres was sufficient to cause death. 

The Brusone Disease of Rice. 

The unusually dreaded brusone disease which manifests itself by the 
appearance of rusty spots in the leaves together with a blackening and 
drooping of the blades, has often been the subject of earnest study, ever 
since Garovaglio in 1874 began investigating it. The majority of investi- 
gators considered the phenomenon parasitic. Some thought it necessary to 
assume bacteria to be its cause, and some held various fungi responsible, — 
among others, Piricularia Oryzae Br. et Cav. 

Recently, however, Brizi'' has made comparative cultural experiments 
from which it becomes evident that an exclusion of air from the roots in 
high temperatures in water cultures induces disease of the plants with the 
phenomena of the Brusone disease. With these experimental results agree 
very well the discoveries which have been made in Italy and Japan. It has 
been especially observed that the Brusone disease usually appears if com- 
pact, only slightly pervious soils are healed greatly and a rapid change of 
temperature sets in. There then follows an affection of the root which 



1 Bot. Z. 1880, p. 143. 

2 Landwirtsch. Versuchsstationen, 1872, No. 2, p. 133. 

3 Brizi, U., Ricerche sulla malatti del riso detta Brusone. Ann. Instituto agrar. 
Ponti. 1905. Milano. Cit. Zeitschr, f. Pflanzenkrankh. 1906. 



3i6 

brings disease of blades in its train and only later do parasitic organisms 
infest the diseased parts. 

We consider Brizi's experiments as decisive and think that suffocation 
of the roots during high temperature, which greatly increases the leaf activ- 
ity, is the first impulse to the disease. The soil should be aerated at once. 

The Diseases of Gladioli. 

A phenomenon of disease, not rare in cultivating gladioli in heavy soils, 
or on pieces of ground with a lighter soil, but a higher ground water level 
in wet years, may be traced to a lack of oxygen. The disease manifests 
itself in the often sudden aeath of the plant at a time when the inflore- 
scence is already developed. At first the lower leaves seem marbled with 
yellow (noticeable at first only when the light falls through them). The 
chlorophyll bodies decompose and leave yellow drops which look like oil. 
While this process advances apparently in stripes between the veins in the 
aerial parts of the leaves, brown, depressed places are found on the leaf 
bases still below the soil which initiate a complete decomposition of the leaf 
parenchyma. No real weakening takes place, but the decomposition repre- 
sents a process of humification. Bacteria^ and often also fungi, small worms, 
m.ites, etc., are always found in these tissues which smell sour like humic 
acid. The aerial parts of the leaves dry quickly and become covered with 
black pits of Cladosporium and Altemaria. 

Despite the wealth of parasitic organisms present, the disease should not 
be characterized as parasitic, since the first stages, viz., the brown coloring of 
the ducts and of the parenchyma, lying close to them, are produced 
within the healthy tissue without the co-operation of such organisms. Later 
a number of the duct tubes are filled with a cloudy, brown mass which be- 
comes firm like gum. The latter phenomenon has been observed also in 
other plants, the roots of which were injured by continued moisture in the 
soil and the lack of oxygen thus produced artificially. 

Gladioli like a great deal of moisture in the soil but it should not be 
long continued. In dry years the mistake is often made of watering bulbs 
and tuberous plants every day. This is wrong, the excessive drying of the 
soil must be prevented by mulching with litter. 

k. Changes Due to a Lack of Carbon-Dioxid. 

Despite the small content of possibly 0.036 to 0.040 volume per cent, 
of carbon-dioxid, which the air^ possesses, while consisting of nearly 79 
parts of nitrogen and 21 parts of oxygen, it suffices everywhere for a high 
rate of growth; if this important nutrient substance is entirely lacking, the 
other factors of growth are without value, even in a most favorable com- 
bination, as may be observed experimentally by placing vessels of caustic 



1 According to Jolly's investigations (cit. in Forsch. a. d. Gebifte der Agrikul- 
turphysik. 1S79, p. 325) the oxygen content of the air varies not inconsiderably 
(between 20.53 and 20.86 per cent.). The largest oxygen content is found v^^ith a 
prevailing polar current and the least with a prevailing equatorial current. 



317 

potash under closed bell-jars. Corenwinder^ found that buds and young 
leaves do not develop further in air free from carbon-dioxid. In Bous- 
signault's- experiments two maize kernels developed into plants of which 
the dry weight itself and the carbon and oxygen contents were less than in 
the seed, while the nitrogen content was just as large. Hydrogen and ash 
had undergone a slight increase. Bohm^ found in leaves of the scarlet 
runner bean, cut ofif from the plant during growth, from which the starch 
had been removed by darkness, that these leaves not only formed roots 
from the petioles in full daylight and in an atmosphere containing carbon- 
dioxid, but also increased in breadth even if they were watered only with 
distilled water. On the other hand the seedlings of the scarlet runner bean 
grown in distilled water and exposed to the action of full daylight under 
bell-jars with caustic potash showed only an increase in length up to lO cm. 
while the stems shrivelled below the primordial leaves which as a rule were 
free from starch. Seedlings of the scarlet-runner bean which had been 
grown in garden soil rich in humus but were robbed of all but a small 
amount of their starch by weak illumination, did not form any new starch 
but went to pieces when later strongly illuminated in an atmosphere robbed 
of its carbon-dioxid. Therefore, the carbon-dioxid in the soil and the other 
favorable conditions for growing were of no value. Godlewski* found that 
the starch also disappeared in plants exposed to full daylight if the carbon- 
dioxid of the air was kept from them. 

A further insight into the method of growth of plants from which the 
carbon-dioxid of the air had been removed is given by my own experiments'"'. 
Young cabbage plants were left in a 0.5 per cent, nutrient solution, part 
under bell- jars with caustic potash, part under others without caustic potash 
and the remainder left free between the bell-jars. After ten days the har- 
vest yielded : — 

Bell-jars Bell-.iars 

Uncovered plants with Potash without Potash 

Plant No I. IT. III. IV. V. VI. VII. VIII. IX. 

Fresh weight of root and 

stem 0.457 0.367 0.414 0.470 0.175 0.2305 0.297 0.313 0.232 

Fresh weif?ht of leaves . . 1.598 1.494 1.564 1.682 0.765 1.011 1.736 1.712 1.850 
Upper leaf surface in 

square cm 50.6 47.5 50.1 47.3 25 4 26.6 50.4 54.1 37.1 

Total dry weight 0.2755 0.2510 02.685 0.2760 0,0760 0.0985 0.1705 0.1740 0.1765 

Percentage of the fresh 

weight in dry weight 13.4 13.5 13.5 12.8 8.4 7.9 8.1 8.6 8.4 

Total evaporation in 

grams 69.3 74.4 82.5 75.0 27.4 34.4 43.1 40.4 43.3 

Evaporation per gram 

dry weight 251.5 296.4 307.2 271.7 360.6 349.2 252.8 232.2 245.3 

The table shows that the production in fresh and dry weight was the 
smallest under the bell-jars with potash. The absolute amount of evapora- 

1 Recherches chimiques sur la vegetation. Fonctions des feuilles. Compt. rend, 
t. LXXXII, 1876, No. 20, p. 1159. 

2 Boussingault, Vegetation du Mays, commence dans une atmosphere excempte 
d'acide carbonique. Compt. rend. Vol. LXXXII, No. 15, p. 788. 

n Bohm, in Sitzungsber. d. Wierner Akad. 1876, cit. Bot. Zeit. 1876. p. 808. 

* Bibliographische Berichte iiber die Publikationen der Akademie der Wissen- 
schaften in Kraukau. Part I, cit. Bot. Zeit. 1876, p. 828. 

5 Sorauer. Studien liber Verdunstung. Forschungen auf dem Gebiete der 
Agrikulturphysik, Vol. Ill, Parts 4 and 5. 



tion is greater or less according to the amount of newly produced dry sub- 
stance ; it is smallest in the plants under the bell-jars with potash. Naturally 
the effect of the bell-jars, i. e., the humidity prevailing under them, is to 
be taken into consideration. This factor manifests itself, when compared 
with the uncovered specimens, by the lower percentage of dry weight in 
the plants, i. e., by a loose structure and longer petioles. 

If the specimens from the bell-jars containing pota.-h are compared 
only with those of the other bell-jars, the result is more certain. The lack 
of carbon-dioxid manifests itself most by the lessened total production, 
especially in the leaf apparatus; the upper surface is only about half as 
large. The most striking effect is the amount of evaporation, which is cal- 
culated per gram of dry substance present. This is greatest in the plants 
deprived of the carbon-dioxid supply. Th-e same condition is found in the 
calculation of the evaporation per square centimeter surface in the plants 
grown under both conditions. This fact should be associated with the re- 
sults of other experiments, according to which it is evident that the amount 
of evaporation increases also in plants which lack other nutritive substances. 
If, for example, plants from a normal favorable nutrient solution are placed 
in one of too low concentration, or in distilled water, evaporation is in- 
creased; it increases also in seedHngs after the removal of the organs con- 
taining reserve food, the cotyledons. It may be assumed that the plant 
must force itself to a greater transportation of water through its roots, i. e., 
to a greater one-sided kind of labor, in order to meet lesser amounts of re- 
serve substances contained in the solution due to their increased absorption 
by the roots from the surrounding soil. 

For practical work, the above investigations suggest an attempt to in- 
crease production by increasing the supply of carbon-dioxid. Experiments 
actually show that a much more rapid formation of starch is obtained by 
increasing the carbon-dioxid. In many plants an increase up to 6 to 8 per 
cent, was possible. Of course, a different absolute quantity of carbon-dioxid 
is necessary for each plant and in the same plant for every other combination 
of the vegetative factors in order to obtain an optimum production. The 
strengthening of the vegetative processes by the addition of carbon-dioxid 
manifests itself in the more compact growth and thicker leaves^ 

While previous experiments have taken up the results of a lack of car- 
bon-dioxid for the whole plant, Vochting- tested the behavior of various 
branches, which were left on the normally growing plant, but transferred 
to an atmosphere free from carbon-dioxid. It was found thereby that each 
branch and leaf must be maintained by its own work and that their life 
activity gradually dies away if this work is prevented by a lack of carbon 
dioxid. The plant can, indeed, develop further the branches in the atmos- 
phere free from carbon-dioxid, but the leaves on these branches are a faded 



1 Feodoresoo, E., Einfluss der Kohlensaure auf Form und Struktur der Pflanzen. 
Cit. Centralbl. f. Agrikulturchemie, 1900, p. 137. 

2 Vochting, H., tjber die Atahangig-keit de.s Laubblattes von senier Assimi- 
lationstatigkeit. Bot. Zeit. 1891, Nos. 8 and 9. 



319 

green and form no starch. They also do not recover, if the branch, is 
brought back to air containing carbon-dioxid, but go to pieces after a short 
lime. It thus becomes evident that each leaf has its independent existence 
and that any disturbance of it cannot be adjusted by the organism as a 
whole. The organ which has become functionless is thrown ofif from the 
body. 

B. EXCESS OF WATER AND NUTRITIVE SUBSTANCES, 
a. Excess of Water. 



MOISTURE. 

The phenomena of yellowing and decomposition connected with stag- 
nate water have been considered when discussing the disadvantages of heavy 
soils. We are thus concerned here only with proving by example, how an 
excess of water, like a lack of it, retards production. Thus Stahl- 
Schroeder's^ experiments with oats in sterile sea-sand to which the nutrient 
solution had been added, gave the following results. With the addition of 
water there were produced : 



% of the 


No. 


Weight of 


Weig-ht of 


Medium 




Phos- 


Nitro- 


entire water 


of 


1000 Ivernels 


straw and 


length of 


Ash 


phoric 


g-en 


capacity 


ker- 




chaff 


the plants 




acid 




of the sand 


nels 


S 


g- 


cm. 


7r 


% 


% 


35 


84 


15.5 (calculated) 


6.2 


49 


9 


9 


3.752 


50 


1723 


21.6 


73.9 


102 


2.933 


1.444 


2.915 


70 


2074 


18.5 


101.8 


140 


2.712 


1.090 


2.501 


90 


1S27 


16.3 


115.0 


157 


3,007 


1.207 


2.407 


95 


469 


11.1 (calculated) 


90.8 


162 


5.892 


1.847 


3.444 



Thus only the vessels containing a medium amount of water yielded a 
good harvest in grains. With a larger water content, the harvest of grains 
fell, while the yield in straw increased. With a lack of water in the sand 
(35 per cent.) and with an excess (95 per cent.) none of the grains ripened. 
The poorer the growth of the plants, the greater their percentage of ash con- 
tent, and wealth of phosphoric acid and nitrogen. 

Clogging of Drain Tile. 

Wherever flat lying drains extend through the root systems of perennial 
plants, an unusually luxuriant root growth may stop up the drains. The 
long whip-like, very slender and comparatively thin roots lying side by side, 
like cords, in this way form mats ten or more meters long and as thick as 
the width of the drain allows. The most dangerous tree seems to be the wil- 
low for most of the drain mats seem to be formed by it, yet all plants may 
form similar root-growths and Magnus- once found, for example, the 
rhizome of the horse tail {Equisetum palustre, L.) growing very luxuriantly 
in such a mat. Cohn^ found a drain mat which came from a pipe laid 125 

1 of. Biedermann's Centralbl. f. Agrikulturchem. 1905, Part 2. 

2 Sitzungsber. d. Bot. Vereins vom 26 Mai, 1876. Vol. XVIII, p. 72. 

3 Verh. d. schles, Gesellsch. f. vaterl. Kultur, 25 Oktober, 1883. 



320 

cm. deep and was formed entirely from the ramifications of the root of a 
single Equisetum from which a piece 12 meters long could be separated. 

Miiller-Thurgau experimented with roots from one plant, putting some 
in a nutrient solution, others in distilled water ; each experiment showed a 
stronger growth in the solution. These experiments showed that root 
growth increases locally when the roots reach places containing food sub- 
stances. 

If the drain mats return after removal, it is advisable to take out care- 
fully both trees and roots by uprooting and not by chopping down. If the 
trees must remain it is better (especially with double lines of drainage) to 
lower the surface laid pipes (as a rule between 80 to 90 cm.) to the level of 
the pipe system lying deeper (1.5 m.). 

Sprouted Grain. 

In the phenomena to be cited here which are connected with an excess 
of water, injury is caused either by the fact that water from outside acts 
mechanically on the tissues at an unsuitable time, or the water taken up by 
the roots cannot find utilization and be carried off in corresponding amounts. 
To the first group belongs grain sprouted on the field during the harvest 
because of rain. The disadvantage is the greater in this instance, since the 
sprouted kernels can neither be used for nutritive purposes nor are they 
suitable for seed. Of course the germinative capacity for subsequent use 
as seed decreases according to the amount the kernels have sprouted. 
Ehrhart^ found that the weakness and thus the mortality of the seedlings 
increased as their development had already advanced because of the pre- 
mature sprouting. We owe to Marcker and Kobus- thorough investigations 
of the changes in the seed due to sprouting. The former investigated barley, 
half of which was harvested uninjured, but the other half was left standing 
for almost 14 days, wet through by rain. The differences were shown by a 
determination of the elements soluble in water, for they amounted to the 
following in 

Sprouted and in zvell-harvestcd barley 

Soluble starch 1.17 per cent. 1.76 per cent. 

Dextrin 0.00 per cent. i.io per cent. 

Dextrose 4.92 per cent. 0.00 per cent. 

Maltose .7.32 per cent. 3.12 per cent. 

Other soluble substances... 5.23 per cent. 5.64 per cent. 

18.64 per cent. 11.62 per cent. 

We thus see that the vigorous diastase action has resulted in a very 
abundant sugar formation from the starch and dextrin. The starch con- 
tent had fallen from 64.10 per cent, to 57.98 per cent., because of the 
sprouting. If the kernels are used for making starch, the great amount of 



1 Deutsche landwirtsch. Presse, 1881, No. 76. 

2 Aus Braunschweiger landw. Z., 1882, No. 22, cit. \n Biedermann's Centralbl. 
f. Agrikulturchemie, 1883, p. 326. 



321 

diastase would now presumably convert more starch into dextrin and sugar, 
when softened, and result in appreciable losses in manufacture. The great- 
est changes due to sprouting, however, are found in the nitrogen-containing 
elements of the grain. While especially the ammonia content had remained 
unchanged (nitric acid was not found in quantities worth mentioning in 
either of the two kinds of grain) the soluble proteins had decreased to a 
great extent, the insoluble to a lesser one. This decrease is explained by 
the relatively great increase of the amides. Thus, in sprouting, first the 
soluble proteins had been consumed in the formation of the amides and 
later even a part of the insoluble ones. 

Kobus arrived at the same results in his investigations of sprouted 
wheat, whose gluten content had decreased from 20 to 25 per cent. This 
fact explains the well-known loss in baking quality of a flour made from 
sprouted grain. 

The germinating capacity in the experiments carried out by Marcker 
had fallen from 98 per cent, to 45 per cent. 

It thus becomes evident how worth while are the great efforts which 
must be exerted in any case to make possible harvesting the grain while 
dry. Similar losses may befall other field crops as well, as, for example, 
lupines, rape, beet roots. The cases in which the seed germinates inside the 
fruit without being noticeable externally are interesting but not of importance 
agriculturally. I found such cases in pears, apples, melons, and pumpkins. 
Other observers found the same phenomena in oranges, as well as pumpkins, 
and indeed in other fruits also which had remained very long on the trees, 
and in that which had only colored late. Further statements on this subject 
may be found in the section on germination interrupted by drought. 

The Rupturing of Fleshy Part.s of Plants. 

Fleshy roots, stems and fruits frequently crack open in long periods of 
dampness. Among vegetables, kohlrabi, carrots and parsley suffer especially. 
Hallier^ proved that the rupturing is due to excessive water supply, for by 
hanging parsley roots in water he found after three days that all the part 
which was in the water had cracked open. Boussingault- observed the 
rupturing of cherries, mirabelle plums, pears, grapes, and blueberries after 
the fruits had hung in water. I obtained the same results by imbedding 
them in wet sand. Of herbaceous stems, those of rape crack open very 
freely shortly before the time of blossoming. The figure here given shows 
the change in a bean, which I had planted too deep in wet sand. In July, 
1882, in Proskau. I found ruptured potato stems and Beta vulgaris roots. 
At that time a very rainy July had followed a dry spring after a small 
amount of winter moisture. The phenomenon was apparent at first on light 
places in the soil and in the best developed plants. I found similar cases 
in roses and in plum seedlings, which had been taken from the sand and 



1 Hallier, E., Phytopatholog-ie, p. 87. 

- Compare Bot. Jahresbericht, 187.3, p. 253, 



322 




placed deeper in a nutrient 
solution than they had been in 
the sand. The base of the 
stem split in those specimens 
previously exposed to the air. 
In the souring of crops in 
fields planted with horse 
beans, peas, vetches, etc., 
the base of the stem is rup- 
tured at times above the 
places where the (rotted) 
roots arise, and it is found 
that a spongy, loose tissue 
protrudes from the torn place, 
as in the bean here illus- 
trated. 

All these phenomena have 
one characteristic in common 
—that they are initiated only 
when, after a considerable 
period of normal develop- 
ment, or still more after a 
previous dry period, an un- 
usual supply of water is given 
suddenly. If the plants are 
in contact with water from 
the beginning of their de- 
velopment, they adjust them- 
selves to their surroundings. 
The same adjustment can be 
observed especially in those 
varieties which develop in 
water as well as on dry land. 
Levakoffski's^ experiments on 
Epilohiutn hirsutum, Lycopus 
europaeus and Lythrum serve 
as examples. The compari- 
son of water and land speci- 
mens shows that in the water 
plants, two rows of colorless 



1 Levakoffski. De I'influence 
de I'eau sur la croissance de la 
tige etc. Cit. Bot. Zeit. 1875, p. 696. 



Fig. 42. Bean plant split at the base as the result of excess 
of water. The torn place has scarred over. 



323 

cells, free from chlorophyll, 3 to 4 times as long as they are broad, exist 
between the cambium and the bark parenchyma which are not present in 
the land specimens. This difference becomes greater, when the older parts 
of the plant are compared with one another. Below the surface of the 
water these cell rows become a thick, lacunar tissue Epidermis and bark 
soon go to pieces here. The cells which form this special tissue are de- 
veloped from the cambium. 

The sudden excess of water, which causes the rupturing of part of the 
plant, destroys the equilibrium in the epidermis, or the cork layer present 
instead of the epidermis, and in the fleshy parenchyma body. Especially 
after previous periods of drought, the elements of the upper epidermis be- 
come thicker walled and less elastic and are not able to accommodate them- 
selves rapidly enough to the swelling inner tissue. 

If the rupturing takes place in succulent organs without any previous 
dry period, due to a long continued supply of water in damp surroundings, 
the torn places, as a rule, differ from those due to drought, in that, in the 
latter, the wounded surface turns to cork or is cut off by a new cork layer. 
In the former, on the other hand, the parenchyma cells, exposed by the 
rupture, remain thin walled, at times elongated into pouches and decaying 
easily. Boussingault found that the fruits lost sugar to this excessive water. 
This loss of sugar together with the increased absorption of water may 
explain the watery taste of the fruit after rainy weather. Some blossoms, 
left under water, also lost sugar. On the other hand, in sugar beets, rape, 
in the seedling roots of wheat, barley and maize no sugar was lost although 
the tissue was rich in sugar. 

There is a method of storing zvinter apples which is well worth recom- 
mending, viz., placing the fruit in layers in sand. If the sand is kept too 
moist, a large percentage of the fruit may lose in selling value because the 
skin ruptures. 

Miiller-Thurgau^ made similar observations in related experiments. 
After apples had lain eight months in boxes of earth he found the fruit was 
wet, some of it ruptured, some mealy, and its acid and sugar content much 
lower. The percentage of decaying apples was much less, however, than in 
fruit lying free in the cellar. 

The rupturing of fruits and vegetables, due to storage methods, can be 
overcome by supplying a dry, well ventilated place. In fruit on the tree, 
especially the egg plum which is very delicate, it is advisable in longer 
periods of rain to shake the water from the tops of the trees. 

Finally, attention must still be called to the fact that the tendency to 
rupture can also become hereditary. An observation of this was made with 
cucumbers". In forcing these, the owner always chose for his seed the 
finest specimens of a variety which ruptured easily, and observed that this 
bad condition manifested itself more abundantly and earlier from year to 



1 Funfter Jahresb. d. deutsch-schweizerischen Versuchsstation zu. Wadensweil. 
Zurich, 1896. 

2 Zeitschr. f. Pflanzenkrankh. 1899, p. 183. 



324 

year. He then planted half of his greenhouse with the forcing variety pre- 
viously used and the other half with an outdoor variety. The latter gave 
healthy fruit up to autumn, while the half planted with the first variety 
produced ruptured fruit from the beginning of May on. Such observations 
give hints well worth noticing when choosing seed of vegetables which tend 
to rupture. 

The Woolly Streaks in Apple Cores. 

In describing apple varieties the expression "The carpels of the cores 
rupture," is found stated here and there, as a characteristic of the variety. 
According to the illustration here given, a condition of membranous carpels 
is said to be indicated in which the inner walls of the core divisions are not 
uniformly smooth and solid, but show a surface crossed by streaks which 




Fig. 43. Cut apple, the coi-e of which shows woolly streaks (w). 

look white and woolly, and extend slantingly from the centre to the outside. 
The phenomenon occurs frequently and is considered to be normal,- — which 
deduction I do not care to hold to. Aside from the fact that under certain 
circumstances all the fruit in the same variety does not show such woolly 
streaks and that, in dilTerent years, it is developed to a different degree, 
even appearing in isolated cases in varieties which, as a rule, have a smooth 
core, the conditions found microscopically also prove splendidly the ab- 
normal nature of these streaks. 

If a carpel with such streaks is cut through, as shown in Fig. 43 at w, 
the appearance is found as given in Fig. 44. In this the side designated by 
K is the inner wall of the core, while F indicates the outer side bordering 
on the flesh of the fruit. In varieties of apples with smooth carpels, the 
inner lining of the core is formed only of such cell elements, as are shown 



325 

at p. These are very much elongated, extraordinarily thick-walled cells, 
traversed by many, frequently branched canals ; they turn yellow with 
chloriodid of zinc. Single layers of such cells may cross one another. Ac- 
cordingly, besides such cells seen in full length at p, the same horizontal 
section also exhibits parts of elements in cross-section q. It is evident that, 
because of the close arrangement of the cells on the one hand and because 
of their very strong walls on the other hand, a very great firmness is ob- 
tained in the core tissue, increased by the transverse course of the cells. It 
is evident further, that in fruits with a larger calyx depression, through 
which fungi may grow easily into the core, the spread of fungi, which pro- 
duce decay, is limited by the parchment-like, solid carpels. 




Rupturing- of the papery carpel or the apple, due to the excrescence tissue 
of a woolly streak. (Orig.) 



This protection from internal decay is destroyed by the woolly streaks 
(Fig. 43 W) for they consist of very loose tissue, which breaks through the 
solid walls. 

We see in Fig. 44 that these woolly streaks are formed of thick bunches 
of cell rows elongated like threads, which differ strikingly from the sur- 
rounding ones because of their thinner walls, and very gradually pass over 
into the tissue of the fruit {F), while others are quite sharply and suddenly 
cut off from the thick- walled cells {p) below the places in the core which 
have remained membranous. Only at the base of this bunch of threads do 
short, schlerenchymatous cells {sk) , isolated or lying beside one another in 
mats, recall the elements {p) to be found in the normal wall. Although these 



326 

thin-walled cell rows approximate more nearly tissue of the fruit in form 
and by the blue coloration from chloriodid of zinc, they still do not corres- 
pond to it entirely. The difference consists chiefly in a wart-like thickening 
of the cell wall iv which is most strongly developed in the outer cells of the 
thread bunch, but in the inner cells is often only weakly indicated and 
generally is not present at all in the schlerenchymatous elements. These 
cell wall thickenings which push outward and look like buttons, show, with 
the action of chloriodid of zinc either a pale blue color or remain uncolored, 
or even appear yellow. The latter case is found most distinctly in the very 
thick- walled cells (sk) in which the whole membrane is also colored yellow. 
Fig. 44, at the left, is a more strongly magnified section from a cell row of 
the bunch filament. It is seen here that the wart-like protuberances of the 
wall which I would also like to consider phenomena of the swelling of 
various points in a fine middle lamella, often have mushroom forms (kn)'^. 

Thus it should be assumed, that at the time of the chief swelling of the 
fruit, the tension of the tissues in the carpel has become so great, because 
of a sudden, great supply of water, that the connection in the membranous 
tissues is broken in stripes and loosened and the elements now freed from 
pressure, and not thick-walled, extend like pouches into the hollow of the 
core. 

Varieties inclined to have woolly streaks are especially easily exposed 
in damp years to the formation of moulds, i. e. phenomena of decay in the 
core. It is, therefore, advisable to use these fruits quickly. 

The Ring Disease of Hyacinth Bulbs. 

This disease is very serious for growers of hyacinth bulbs. It manifests 
itself by the browning and loosening up of a scale in the midst of healthy 
bulb layers. The decomposition of the tissue progresses from the neck of 
the bulb downwards into the bulb centre. If it reaches the latter, the bulb 
is as good as lost. The disease is often transmitted to the bulblets. All the 
diseased parts become covered with Penicillium, which here has actually 
taken on a parasitic character. The reason for the extremely rapid spread 
of the fungus is to be found in the change of the substratum which proves 
unusually favorable for it. Analyses show especially that the fresh, healthy 
substance of the ring-diseased bulb possesses more sugar than that of healthy 
specimens. The former resemble younger scales in contrast to the older 
ones. Since now a reduction of the sugar takes place with the increased 
ripeness of the bulbs, we shall have to conclude from the greater amount 
of sugar that diseased bulbs are less ripe. 

In fact it may now be proved that by their cultural methods our bulb- 
growers often run the risk of harvesting unripe bulbs. In taking up the 
bulbs, the grower sometimes does not wait until the leaves have completely 
dried up in summer. This holds good primarily where the hyacinths serve 

1 The same or similar phenomena have been observed very recently by various 
scientists. I found them also in the hair-like cells, clothing the interior of beets 
which had become hollow; in the leaf parenchyma cells of fallen oat plants, etc. 



327 

as decorative plants in gardens and public places. There a bed of old 
liowers and slowly yellowing leaves is very unsightly. Consequently the 
bulbs are lifted and let ripen in another place. The resulting great injury 
to the root prematurely checks the vegetative growth of the bulbs. The 
leaves dry before they have lived out their life and their bases, i. e. the 
scales of the bulbs, remain immature and rich in sugar, thereby forming the 
desired centre for convenient infection by the fungus. 

In the large field-grown commercial bulbs, the supply of fertilizer 
enters into the question, since it is desirable to produce very strong bulbs 
in the shortest possible time. The fertilizer so lengthens the time of growth 
that many varieties have not finished growth at the fixed time of harvest. 
The leaves, still green, then possess in every case unique scales and during 
the storage of the harvested bulbs on the "bulb floors," up to the time of the 
autumn sales, Penicillium has ample time to attack the scales, which remain 
rich in sugar, and to destroy them. It is a matter of course that varieties 
ripening especially late will exhibit this bad condition and the growers, 
therefore, speak of "ring diseased races." 

The testing of the bulbs is accomplished by cutting superficially through 
the tip of the neck during the dormant period. If the cross-section shows 
a brown ring between the white scales of the bulbs, these bulbs should not 
be sold. 

Stock suffering from the ring disease can be cured by putting the bulbs 
in sandy soils, not freshly manured, with a deep lying ground water level, 
where, with scarcity of nutriment and moisture, they can ripen early. 

The fact still remains to be mentioned that a phenomenon has been con- 
fused with the real ring disease, which is very similar to it judging from its 
habit of growth\ The cause is known to be a nematode {Tylenchus 
Hyacinthi Pr.) which can wander into the scales from the leaves. In this 
disease, however, a gall-hke distension of the cells takes place, also the 
formation of cork walls like little islands and other differences, as has been 
described more in detail in the second edition of our manual. 

Springing of the Bark. 

In illustrating the ruptured bean plant (Fig. 42), we noticed that a 
soft tissue mass had protruded through the gaping split in the cracked stem. 
This is the new formation of bark tissue, which may be considered a re- 
action of the organ to the wound stimulus and the decreased tension. Other 
cases, however, occur in which matters are reversed, viz., that the increase 
of bark tissue is the primary process and the splitting, the secondary one. 
Such an increase in growth can arise from different causes. Hartig- con- 
siders one of these to be the increase in size caused by a sudden isolation 
of forest trees. He describes cases of hornbeams in a beech grove, where, 

1 Journal de la Soc. nat. et centrale d'Horticulture de France. April, 1881. 
Sorauer, Zur Klarung- der Frage liber die Ringelkrankheit der Hyacinthen. Wiener 
illustrierte Gartenzeitung-, 1882. April number, p. 177. 

2 Hartig, R., Das Zerspringen der Hainbuchenrinde nach plotzlicher Zuwachs- 
steigerung. Untersuch. forstbot. Inst. Vol. Ill, p. 141. 



328 



after isolation. — "the breast high growth, measuring 1.2 sq. cm. in cross- 
section, in a few years increased in cross-section growth to 13.7 cm. ann- 
ually^." The cork was split thereby in numerous places and resulted in a 
rupturing, indeed, in places it lifted the bark body from the wood-cylinder. 
Hartig found similar conditions in oaks and explained this by a greater 
soil activity, resulting from the isolation and increased action of light". 

Phenomena of this kind may be found also in other trees, especially in 
parks and gardens. 

Shedding of the Bark. 

Hartig describes a case in which the splitting of the bark is due to an 

increase in the normal 
growth. I observed a 
splitting and shedding 
of the bark from an ab- 
normal cell - elongation 
in the bark parenchyma. 
In 1904, I found in an 
avenue of elms a num- 
ber of trees standing 
side by side at the bases 
of which a great many 
pieces were perhaps as 
long as one's hand. 
Upon closer investiga- 
tion, loosely hanging 
strips of bark 25 to 50 
cm. long were found on 
the lower end of the 
trunk, which could easily 
be removed. The trunk, 
thus exposed, was cov- 
ered with greenish tis- 
sue in spots which 
proved to be new for- 
mations of bark. The 
loosened pieces of bark 
(Fig. 45), exhibited on 
the inner side flat, light brown cushions irregularly distributed and differing 
in size and thickness. Having a spongy consistency, they easily gave way 
to the pressure of a finger-nail. Here and there, between them could be 
seen crater-like, harder, small protuberences. The upper surface of the 
cushion was smooth ; it was rough and sometimes woolly in places because 
of prominent, hair-like processes. The part of the bark remaining on the 




Fig. 45. Inner surface of a fallen piece of elm 
bark, with cushion-like, protruding tissue islands. 
(Orig.) 



1 Lehrbuch der Pflanzenkrankh, 1900, p. 261. 
3 Unters. Vol. I, 1880, p. 45. 



329 



tree appeared a yellowish green and juicy. It consisted of bark parenchyma, 
which had originated from a healthy cambium. 

The subjoined Fig. 4() 
pictures the bark about to 1^ 
be shed. At h is shown . 



5^- 




the old wood ; at nh the 
last produced new wood ; 
g indicates ducts ; c the 
cambium. Next this lies 
the normal, young bark 
which gradually passes sp.- 
over towards the outside 
into the broken older bark. 
In reality the extent of 
loosened older bark is 
much greater in proportion 
to the normal young bark 
than is shown in the draw- 
ing, because of lack of 
space. The normal inner 
bark has a very regular 
structure, in which layers 
of porous bark parenchyma 
alternate regularly with 
flat bands of slender cells 
(/) which might be difTer- 
entiated as "wedge-cells." 
These slender cell bands 
would correspond to the 
"pressure wedges" men- 
tioned in connection witli 
the tan disease. The cells 
forming these wedges ap- 
pear in longitudinal section 
as long as in cross-section, 
nearly colorless, with pe- 
culiar, wide-meshed wall 
thickenings, looking like 
irregular wedges. The 
parenchymia lying between 
every two such thin, slen- 
der bands of wedge cells is 
proportionately large-celled, porous and rich in starch. Deposited in it 
are large, hard bast bundles, {h) with the rows of calcium oxalate crystals 
accompanying it (o) and the cells {si) containing mucilage. 



FiS'. 46. 



mst 

Elm bark with bark excrescence. 



(Orig.) 



330 

These alternating tissue layers are separated by broad curved medul- 
lary rays (mst) which even in the entirely healthy bark can exhibit a wavy 
course, but in the diseased bark may often be displaced and take a hori- 
zontal course. The sharp curvature is caused by the spreading apart of the 
parenchyma cells which, containing chlorophyll and lying between the slen- 
der bands of wedge cells, elongate into pouches, and for a long time contain 
a great deal of starch. They also press outward the hard bast bundles and 
the rows of oxalate crystals. This great layer of separation is covered by a 
plate cork layer extending irregularly into the tissue and often accompanied 
by full cork (t) and the suberized bark tissue cut ofif by it which belonged 
to the earlier period of growth (k). The cork layer often curves spherically 
into the pouch-like spongy tissue (sp) and forms the hard, crater-like points 
on the under side of the loosened bark scale, which were mentioned at the 
beginning of this description. The process of loosening the bark tatters is 
completed on the boundary between the hard tissue of the suberized cortex 
of the previous year, and the soft pouch-like parenchyma. The upper sur- 
face of the separating cushions appears woolly and rough, or smooth, 
according to whether the pouch-like parenchyma clings more or less strongly 
to the separating surface. 

In the elongation of the parenchyma these out-pushings differ from the 
tan disease in which cork excrescences are concerned essentially. 

von Tubeuf^ describes a case of the Weymuth pine very similar to that 
on Ulmus, only no shedding of the bark strips could be observed because 
of the smoothness of the bark. The pine was diseased and covered with 
cushions of Xanthoria parietina. Among these lichens were found blister- 
like processes, of which part appeared to be split and were produced by a 
distention of the bark tissue. The resin ducts were enlarged, the deeper 
bark parenchyma cells elongated into pouches and poor in chlorophyll. 

von Tubeuf's statement that he had produced very similar knob-like 
processes on a branch by wrapping it with cotton wadding which was kept 
constantly moist, warrants the assumption that, in the cases above described, 
we perceive the action of a local excess of water. 

The same kind of processes as these in the bark have been observed 
on roots also. vSome years ago a serious disease of the grapevine was re- 
ported from near Lindau". Its effects were similar to those caused by the 
rust fungus, but it could not be proved to be of parasitic origin. The part 
of the trunk beneath the soil and the older roots exhibited tears i to 3 
cm. long from which protruded calluses, white at first but later turning a 
chocolate brown. The lateral roots near these calluses died. The calluses 
consisted of bark parenchyma cells abnormally lengthened radially and 
scarcely connected any longer. The American varieties, scattered among 
the diseased European vines, were found to be unaffected. As is well- 



1 V. Tubeuf, Intumescenzenbildung: der Baumrinde unter Flechten. Naturw. 
Zeitschr. f. Land- u. Forstwirtsch. 1906, p. 60. 

2 Kellermann im Jahresber. d. Sonderausschusses f. Pflanzenschutz. Arb. d. 
Deutsch. Landw.-Ges. 1892-93. 



331 

known, the extremely luxuriantly growing American vines consume much 
greater amounts of water. 

Tissue warts of this kind are much more abundant than is generally 
assumed and occur also on decorative plants^ They are reactions of the 
plant body to a wound stimulus or internal disturbances of equilibrium in 
the supply of water and nutritive substances. 

Watersprouts. 

By the term watersprouts, watershoots, or suckers, are understood ex- 
ceedingly vigorous foliage shoots with long internodes, which grow up 
perpendicularly from old branches or trunks. Often trunks covered with 
lichens are distinguished by abundant sucker formation. Since the suckers 
grow up into the crown of the tree, they produce wood, and, indeed, un- 
fruitful wood, at the very places which it is desirable to keep free from 
branches in order that sufficient light and air may reach -the inner part of 
the crown. It is not advisable, however, to remove the suckers, if the 
cause of their formation is not removed at the same time. In many cases 
the cause may be found in an impervious subsoil. The roots of the vigorous 
tree reach this impenetrable layer sooner or later, which not infrequently is 
a vein of closely cemented sand containing iron. The absorption of food 
stuffs is limited by this, the tree forms only short shoots and smaller leaves, 
but still bears fruit. In a warm and damp spring, when all trees make a 
strong foliage growth, the energy of the weakened tree also appears to be 
Increased by the favorable vegetative conditions. The strong upward force 
of the water causes the formation of adventitious buds or stimulates dor- 
mant buds, especially those not too far distant from the central trunk, since 
the upward force of the water and the nutrition is much more energetic in 
a perpendicular direction than in the more inclined position. Gardeners 
know how to turn this to use in growing plants on trellises. The horizontal 
branches on one side of the mam trunk, which are weaker than the corres- 
ponding ones on the other side, are held in a perpendicular position for a 
year. This treatment results in a much greater and more rapid growth 
and development. With the production of water shoots a gradually in- 
creasing inequality in nutrition sets in, at the expense of the older, more 
horizontal branches which now suffer from scarcity of nourishment. This 
explains the death of the tip twigs of older lateral branches which begins 
with the appearance of the water shoots. One part of the tree starves when 
some other part develops very luxuriantly. 

As has been said, it is scarcely advisable to remove the water sprouts 
during such a disturbance in the equilibrium of nutrition, rather, it is more 
advantageous in older trees to graft them with valuable varieties and, at 
the same time, to saw off a part of the older branches, so that the tree is 
thus rejuvenated. In places where the sub-soil cannot be opened up easily 



1 Sorauer, P., tJber Rosenkrankeiten, Zeitschr. f. Pflanzenkrankh. 1898. p. 220. 



332 

the evil can be checked for a considerable number of years by using ferti- 
lizers at some distant from the trunk. The tree in its endeavors to reach 
the fertihzer develops a new vigorous root system. Young trees can be 
entirely cured by transplanting. 

It must also be emphasized that the formation of suckers disappears 
of itself from many trees after a few years. This is the case where such 
water sprouts have been induced by an excessive pruning of the tree or the 
sudden dressing of the trunks. In avenues of trees, or along streets with 
telephone wires, and in tree plantations, through which a street or railroad 
line has been cut, a strong development of suckers is found on the sides 

of the trees toward the 
street. 

In such cases large 
branches are often sim- 
ply chopped off on the 
side toward the street. 
Since the root system 
remains unimpaired, it 
pumps up just as much 
water as before the tree 
top had been reduced. 
By the removal of 
the branches, however, 
there is less consumption 
and consequently dor- 
mant buds are awakened 
M'hich mature into slen- 
der shoots, becoming 
water sprouts whose 
buds often sprout even 
in the year of their pro- 
duction. Th. Hartig^ 
has observed that these 
premature shoots de- 
velop no basal buds. 

If suckers are pro- 




Fit 



47. Fasciated branch of Picea excelsa. 



The origfinnl band-like shoot iJ), in one year, has developed three siu:- 

cessive stages which sprout out from one another (J. .?. ■/). {a) Bud 

scales. (K natural size. After Nobbe.) 




Fig. 48. Cro.ss-section of the fasciated spruce branch. 

A through the upper part of the branch; B through the lower part : 

(a) bark with needle cushions; '^b) wood; (^i) pith. 

(Natural size. After Nobbe). 



duced by the sudden re- 
moval of large branches from the crown, their formation may be retarded 
by creating other diverting centers by scarification. In the spring pruning 
of branches, scarifying will, indeed, prevent the formation of the water 
shoots. In the same way, chopping into a vigorous root near the base of 
the trunk at the side where the tree crown has been greatly thinned out. 
will decrease the supply of water and prevent the sucker formation. 



1 Vollstandige Naturgeschichte d. forstl. Kulturpflanzen, p. 176. 



o ^ '7 

Union of Parts. 

We may likewise consider as due to local over-nutrition the con- 
dition arising when a cylindrical branch becomes broad and flattened. It 
then looks as if a number of branches had grown together; nevertheless, 
this is only rarely the case, for almost always only a single branch is in- 
volved which, by broadening its vegetative point, no longer has a vegetative 
cone at its apex, but a comb-like vegetative surfaced 

In the illustration of a spruce fasciation here given (Fig. 47) we recog- 
nize the fact that the broadened axis is a single unit, first by the continued 




Fig:. 49. Fasciation of AInus glutinosa. 

I /< natural size. After Nobhe). 



spiral position of the needles, especially at i and 2, and further in the cross- 
sections A and B (Fig. 48), of which the pith and wood form a single 
connected, uniform surface, and do not show any possible coalescence of 
many single adjacent rings, as must be the case where fasciation is produced 
by the coalescence of many branches originally separated. This theor^^ is 
not changed by a consideration of the fasciation of the alder (Fig. 49), in 
which, besides the unusuallv characteristic crook-like bending of the 



1 iJber Pflanzen-Verbanderung-. Referat in Bot. Zeit. 1867, p. 232. 



334 

branches, resulting from a one-sided increase of growth, we can also per- 
ceive the splitting of cylindrical branches from the band bodies which 
occurs more frequently in deciduous trees. Thus the material for many 
axes, which can be isolated, lies accumulated in the fasciated stem, while 
the stem itself is a unit. 

We can speak only hypothetically as to the production of the fasci- 
ations, which are characterized as hypertrophies by the great increase of 
the leaves and cords of the leaf spurs. An axis, which fasciates later, must 
originally have suffered some arrestment. We have seen already in roots 
held fast between split rocks that pressure from two opposite sides may 
give the axis a band-like form. Under certain circumstances such a changed 
direction of growth may continue if the cause of arrestment itself has dis- 
appeared. Thus Treviranus cites an observation on the stem of Tecorna 
radicans which had become band-like from pressure against the wall, but 
still remained band-like, after it had grov/n far out over the wall. Here 
the branches, which developed further, also became band-like in places. 

Besides such lateral pressure, in other cases a transitory pressure from 
above may also probably cause a broadening of the vegetative point into a 
vegetative surface, and such pressure can possibly be produced by the ab- 
normal behavior of the bud scales (delayed loosening due to resinification, 
drying, etc.). In case no abnormal increase of pressure occurs, direct in- 
juries to the vegetive tip may cause the increase of the vegetable points. 

If the fasciation has once been produced, it can be propagated by 
cuttings ; even under certain circumstances it can be proved constant in the 
seed, as is seen in the favorite garden plant, cock's comb (Celosia cristata). 
The capacity for fasciation may be presupposed in all plants and actually 
observed cases have been reported in great numbers (150) by Masters^ 
As mentioned already, the fasciated growth produced by a band-like fasten- 
ing together of isolated axes, should be distinguished from real fasciation. 
T-opriore- has produced such cases artificially in roots. 

Compulsory Twisting (Spiralismus Mor.). 

A. Braun'' characterizes by the above name, those malformations of 
the stem which corsist of barrel-like distended places in which the grooves, 
extending down from the leaves and representing the vascular bundles be- 
longing to them, exhibit an extreme, spiral twisting. At times the barrel- 
like swelling is so great that the stem splits in the direction of the spiral 
twisting and divides into a number of spiral bands at these diseased places. 
Schimper has named this disturbance in growth "Strophomania." The ma- 
jority of cases are known in the families of the Dipsaceae, Compositae and 
the Rubiaceae. Single examples are described also, for the Labiates, 



1 Masters. Vesretable Teratology, 1869, p. 20. (Compare Penzig- and the isolated 
cases in the Bot. Jahresberichten.) 

2 Liopriore, G., Die Anatomie bandartig-er Wurzeln. Cit. Zeitschr. f. Pflanzen- 
krankheiten, 1904, p. 226. 

3 Sitzungsberichte naturf. Freunde z. Berlin. Cit. Bot. Zeit. 1873, p. 11 and 20. 



335 

Scrophulariaceae, Cruciferae and, among monocotyledons, Asparagus, 
Lilium, Orchis, Triticum, etc., and also in Equisetum. 

We think it justifiable to consider the compulsory torsion- as a fasci- 
ation which has swollen up like a barrel. The cases have no agricultural 
significance. 

Differing from them is the increased spiral twisting of normally con- 
structed woody trunks, which we trace to an arrestment of the growth in 
length (usually resulting from a lack of water and nourishment). 

Dropsy (Oedema). 

a). In Small Fruits. 

Since the propagation of standard gooseberries and currants by budding 
on vigorous shoots of Rihes aureum has found wider distribution, there has 
been a great increase in the complaints of a disease of the stock which makes 
doubtful the success of the budding. 

This disease has been called "dropsy" by growers and consists in the 
appearance of closed bark tumors, i. e. of bark swellings entirely covered 
by the outermost cork layers, or of swellings rupturing later (Fig. 50 A). 
These swellings of the bark are sometimes small, but they may reach an 
extent of several centimeters. They are formed either on one side of the 
trunk or surrounding it, spreading into one another. They appear most 
abundantly on wood two or more years old, yet they can also occur in great 
numbers on branches one year old and directly cause their death, while the 
wood of the older branches may become diseased, to be sure, but does not 
directly die. 

When, as is the custom at present, Ribes is grafted indoors in the 
spring, rupturing tumors are found frequently directly below the place of 
budding. In such cases the bud does not grow. But in extreme cases the 
same kind of swellings may also be found further back from this place, on 
the trunk between every two buds, as wxll as near the buds or, rather, the 
branches already developed from them. Cases are observed in which the 
base of a shoot left standing on wood one or two years old, has swollen 
up like a barrel and is covered by loose, hanging strips of bark. The branch 
above this place is dead. 

As soon as the bark layer, which forms the outer skin of the branch 
and covers this fresh swelling, has split, the swollen place, pushing out from 
under it, exhibits a yellowish, spongy, soft, callus-like tissue-mass con- 
sisting of cells, elongated to pouches, very poor in contents but rich in 
water. (Fig. 50 5 s). This is the former normal bark of which the cells 
beginning in the region between every two groups of bast cells (Fig. 50 5 &) 
have elongated extraordinarily in the direction of the trunk's radius at the 
expense of their contents, otherwise rich in green coloring matter. They 
have partially separated from one another, and, by their constantly in- 
creasing extent, have finally ruptured the outermost oldest bark layers 



336 



(Fig. ^o B e k) which no longer participate in the changes and are sep- 
arated prematurely by the cork layers {k) from the tissue lying beneath 
them^. 

The full thickness of the bark is not always attacked by the pouch-like 
elongation ; in very severe cases, however, even the cells of the cambial 
region are deformed {c). The wood is no longer normal. Instead of normal 
mature wood, consisting of thick-walled, elongated wood cells and ducts, 



(•1 


l(J 


1 1 


-^ 
^ 


1 


! 


1' 


M 


1 

1 


1 


0A 




Fig-. 50. Dropsy in Ribes aureum. (Orig.) 



with cross walls broken through like ladders, a wood is produced, composed 
of short, broad, comparatively thin- walled, parenchymatous cells {h p) . The 
cross-section (Fig. 50 5) shows the transition of the healthy side of the 
branch (A'') into the dropsical side {W) ; h indicates the normal wood. At 
the time when the layer st was produced, the disease manifested itself in the 



1 Compare Sorauer in "FreihofE's Deutsche Gartnerzeitung" August 1, 1880, and 
Goschke in Monatsschrift d. Ver. z. Beford. d. Gartenb, October, 1880, p. 451. 



337 

cambium and the result was that, from there down on the diseased side, 
parenchyma wood {h p) was formed wdiich at the left ended in a medullary 
ray (m). Still further towards the left, normal wood was produced at the 
same time. The same difference is found in the youngest bark parenchyma 
{t p). Because of the great radial elongation of the cells on the dropsical side 
(W) the hard bast cords {h) are pressed out like bows and the cell rows, 
containing calcium oxalate (o), which accompany the bast body, have also 
been correspondingly misplaced into steeply ascending, irregular rows. At chl 
are groups of parenchyma which have remained rich in chlorophyll. It is 
evident that this loose structure of the tissue, rich in water, which forms 
the swelling, has no great permanency. In dry places and with increasing 
dryness in the air, this tissue turns brown rapidly, shrivels, collapses and 
forms a soft, brown mass, part of which remains clinging to the wood, while 
part sticks to the outer bark tatters which roll back in times of drought and 
spread out, gaping, from one another. Such stems of such plants then 
have a rusty appearance and are best excluded from cultivation. Because 
of the ease with which such stock can be grown on strong soils, the loss 
from the disease would be less important, if it did not attack directly the 
potted specimens which have been budded and if the number of budded 
plants was not considerably decreased thereby. 

I am not of the opinion, often expressed in general practice, that an 
over-abundant feeding of the plant is to blame, but I think that an excess 
of water makes itself felt in some places on the axis. If there should be 
an accumulation of plastic food material here at the same time, it would 
manifest itself preferably by an abundant cell increase. But this is not the 
case. If the cells on the healthy and on the diseased sides are counted, only 
an insignificant preponderance is found on the side attacked. Accordingly, 
an abnormal cell elongation is chiefly concerned here. 

This is explained by the treatment of the Ribes stems during the 
preparation for budding. In order to obtain slender stems, growing tall 
rapidly, the other sprouts, produced at the sides, must be removed and 
even the lateral branches on the young stock must be cut back. 

If now the stock is well rooted, it will grow rapidly in the greenhouse 
and the buds, scantily present because of the earlier pruning, are still fur- 
ther decreased by the fact that the shoots developing from them are cut 
back or entirely removed. By cutting off the branches, the amount of water 
forced up by the water pressure is increased in the main axis and manifests 
itself in a pouch-like elongation of the younger bark cells and in the forma- 
tion of tumor swellings which finally rupture. 

My attempts to produce dropsy by abundant watering and the rapid 
("crcing of well-rooted specimens in the greenhouse, together with a con- 
tinued removal of the developing lateral shoots, gave very favorable results. 

The disease will be prevented if the budded stock is not forced too 
rapidly and the sprouts from the bud are cutting back carefully, but not 



338 

entirely removed. Maurer^ has recommended the use of Ribes nigrum in- 
stead of R. aureiim for budding stock. However, I have also known of 
cases of excrescences on the axes of the black currant, especially after the 
transplanting- of such plants as tend to sterility. 

b). In Stone Fruit.s. 

It may be foreseen that, with the present methods of culture, phenom- 
ena similar to those observed with Ribes, will also appear in other vari- 
eties, for our fruit trees are becoming more and more delicate, due to the 
great increase in nutrition supplied them. The mass of the parenchy- 
matous branch substance increases constantly in comparison with the 
prosenchymatous tissues. Between unbudded, wild stock, and budded 
varieties there are considerable differences. Direct measurements have 
shown me that the branches of the cvdtivated varieties acquire a fleshier 
bark while the wood ring decreases considerably in thickness-. I have 
called this increasing tendency of our fruit trees to form soft, parenchy- 
matous tissues, storing up reserve substances, at the expense of the breadth 
of the wood ring, " parenchymatosis." 

In special cases this change in development acquires such extreme pre- 
ponderance that diseases arise. I observed such diseases especially in the 
fruit wood of pears which is often shortened up to barrel-like fleshy swell- 
ings ; growers call these "Fruchtkuchen." The morbid disturbance con- 
sists either in the shedding of the cork layers and outermost bark layers in 
shield-shaped pieces from the side of the branch, thus showing a greenish 
yellow callus-like tissue mass, or in the uplifting of the bark itself in stiff', 
crumbly scales, like rings extending almost around the whole branch, with 
similar changes in the tissues. In the latter case, all the branches found 
above such a place are dead. 

If the diseased condition manifests itself in a less luxuriantly developed 
fruit wood, which may be distinguished from the "Fruchtkuchen," as fruit 
spears, a complete casting of these twigs was often found resembling that 
of the normal dropping of the twigs observable every year in poplars. In 
the present abnormal dropping in pears, the exposed surface was not smooth 
but uneven and woolly, light colored, however, like the cross-section of 
healthy wood. 

A cross-section through a place in the branch which is found in the 
first stages of the disease, shows that the bark has developed strongly on 
one side, especially within the primar\^ bark. Its parenchym.a is thin-walled, 
vesiculated in places or pouch-like and extremely porous. 

A comparison of the pith in a branch which has split and in a healthy one 
of equal age shows that the former is one-third larger than the latter, while 
the wood ring is only one-third as wide. Significant structural differences 
are connected with these misproportions. While a healthy shoot shows 



1 Der Obstgarten, 1879, p. 182. 

- Sorauer, P. Nachweis der Verweichlichung- unserer Obstbaume durch die 
Kultur. Zeitschr. f. Pflanzenkrankh. 1892, p. 66. 



339 

normal libriform fibres and an abvmdantly developed vascular system, the 
wood of the diseased branch is made up almost exclusively of parenchy- 
matous thin cells, between which the vascular cords are deposited. In 
normal trees, under certain circumstances, the weakness of the wood ring 
can be compensated for by schlerenchymatous elements in the bark\ 

The dropsical branches of pears differ from those of Ribes in that the 
wood body is also involved in the parenchymatosis and entirely broken up. 
By the rounding up and dilation of the wood cells, which have become par- 
enchymatous, the ducts are gradually curved, displaced and finally torn. 
Just as soon as the loosening process has affected the whole extent of a 
fruit spear, or a "Fruchtuchen," dropping follows. 

The diseased branches came from trellised trees in a well watered 
garden, richly fertilized with cow-manure. 

Even if such extreme cases are less frequent, yet the first stages, con- 
sisting of the widening and excrescence of the medullary rays and the pro- 
cesses of elongation in various groups of bark cells, are often observed. 

Swellings on the St. John's Bread Tree. 

Swellings often appear as a result of cell elongation and cell increase. 
Savastano- reports thus, for example, of the outgrowths on the branches of 
Ceratonia Siliqua. Conical outgrowths, rich in tannin, are found at the 
tips of the flower stalks, causing atrophy of the blossoms. In an earlier 
study^, he describes the production of larger swellings on the St. John's 
Bread tree. On normally developed fruit branches, in the beginning of the 
disease, the fruit falls in the first stages of development and the remaining 
basal part of the axial cone begins to swell. The repetition of this process 
in succeeding years produces a knotty swelling which can attain a very con- 
siderable size and a height of 6 to lo cm. The bark of this hypertrophied 
tip of the fruit twig is often seven times as thick as that on the normal 
fruiting wood and the wood itself consists of ductless wood parenchyma. 
In the almost pithy bark, the bast fibres have wider lumina and take an 
unusual course. The medullary rays are twisted, the wood ring is often 
bent. In the parenchyma, various cell groups with discolored walls and a 
gummy content are recognizable. From the beginning of the disease, the 
tannin content of the sweUing increases, causing a distinct disturbance in 
lignification. 

A case described by Vochting* in Kohlrabi plants may be mentioned 
here. If all the vegetative points were removed, the leaf cushions swelled 
to extensive structures. In the normal wood of the axis, as in the leaf 
cushions, the cambium developed thin-walled xylem elements. In similar 



1 Pieters, A., The influence of fruit-bearing on the development of mechanical 
tissues in some fruit trees. Ann. of Bot. Vol. 10. London, 1896. P. 511. 

- Savastano, L., Tumori nei coni gemmarii del carubo. Boll. d. Society d. 
Naturalisti in Napoli. 1888. Vol. II, p. 247. 

3 Savastano, L., Hypertrophie des cones a bourgeons (maladie de la loups) du 
Caroubier. Compt. rend. 12. Janv. 1885. 

4 Vochting, H., Zur experimentellen Anatomie, cit. Bot. Jahresb. 1902. II, p. 300. 



340 

experiments with Helianthus annuus Vochting found little tubercles formed 
on the roots. I observed barrel-like thickenings of the sharply bent roots 
of sweet cherries. 

The swellings, described by Warburg^ in the branch canker of the kina 
tree on damp soils, may also represent such correlation phenomena. 

Retrogressive Metamorphosis (Phyllody). 

If the organs of a morphologically higher developmental stage seem 
transformed into those of a lower one, we speak of a retrogressive meta- 
morphosis. The change in the blossoming organs is pathologically of mo- 
ment only if the sexual apparatus, by changing into a group of vegetative 
organs, loses the purpose for which it was designed and thereby initiates 
sterility. 

These cases are listed under the group of phenomena caused by excess 
of water and nutriment, in accordance with the following theory. The 
development of the vegetable organism depends upon two factors, the con- 
stitution of the organic building materials and the way in which they are 
utilized. With the assumption that the first achievement of the organism, — 
assimilation, i. e., the formation of new dry substance, — takes place in a 
normal way, the development of the plant depends upon the way in which 
this organic building material is utilized. In this we recognize two directions 
which we will keep separate as the vegetative and the sexual generations. 
The latter is initiated usually by the appearance in the organism of an often 
clearly recognizable dormant period in the production of its vegetative 
apparatus. As a rule, new leaves are not formed at this time, the apical 
growth of the twigs stops. In place of this the process of the storage of 
reserve building material becomes conspicuous. 

We find this storage process initiated and favored by a decrease in 
the absorption of water with increasing light and heat. An increased con- 
centration of the cell sap is required, if the reserve substances, for ex- 
ample, are deposited in the form of starch. If such a concentration cannot 
be obtained under any circumstances whatever and the building substances 
remain in a diluted form, — for example, sugar, — only a slight impetus is 
necessary to start up vegetative activity. Thus, a certain antagonism pre- 
vails between the two developmental phases, which we may consider as 
transmissable adaptations to atmospheric conditions. After a cool wet 
period when the plant takes mineral substances from the soil and through 
the production of the leaves causes the chlorophyll apparatus to attain to 
its richest possible development, a warmer, drier period follows which 
makes possible the greatest amount of light. In this period the sexual 
organs are formed from the finished, plastic building materials prepared 
in the leaves and develop further, after a shorter or longer dormant period. 



1 Warburg, O., Beitiag zur Kenntnis des Krebses der Kinabaume auf Java. 
Cit. Bot. Centralbl. 1888. Vol. XXXVI, p. 145. 



341 

The more the plastic material is worked up by the leaves, the more 
numerous and perfect are the sexual organs formed within this dormant 
period. The manner in which these primordial buds subsequently develop 
depends on the nature of their further nourishment. If influences make 
themselves felt which are necessary for the maturing of the vegetative 
organs, foliage leaves will develop and, indeed, either from the newly 
formed centres or from the already existing primordia of the sexual gene- 
ration. Thus "phyllody" takes place. 

From our experience in horticulture, we know that an abundant supply 
of nutritive substances with a simultaneous increase in warmth and mois- 
ture, usually at the time of a lesser light action, are conditions initiating 
and favoring the process of phyllody. This becomes especially apparent 
in the production of double flow'ers, in which the stamens are transformed 
into petals. 

Since this process can become hereditary, like all changes in the di- 
rection of growth, where conditions remain equal, and may be increased, 
it is evident that we will find examples in which the tendency to the retro- 
gression of the sexual organs into forms of morphologically lower develop- 
ment, has affected all parts of a flower, and then the whole blossom turns 
green. 

Of course, the influence of the soil is rarely the direct cause of phyllody. 
This is due rather to definite combinations of all the factors of growth, as 
already mentioned, and also occurs not infrequently as a correlation phe- 
nomenon resulting from the suppression of other processes of growth. Thus 
phyllody of individual flowers and inflorescences is produced by injuries 
to the vegetative axis and by vegetable and animal attacks (mites). For 
example, C. Kraus^ removed leaves from Helianthus annuus plants of differ- 
ent ages, leaving only the bracts of the blossom head. In the older plants 
the bracts curled back and enlarged prematurely. In the younger plants 
25 per cent, showed an actual phyllody, since the bracts assumed, more or 
less, the form of foliage leaves. 

In my freezing experiments, I have often observed that the bud scales 
were transformed into herbaceous, leaf-like organs after the apical portion 
had been destroyed by frost. GoebeP obtained similar results by removing 
the leaves of young plants of Prunus Padus, Aesculus, Rosa, Syringa and 
Quercus, and then putting the plants into plaster casts. 

Teratology has classified the phenomena. The simplest case is 
"virescence," turning green, in which an organ of the flower retains its 
form in all essentials, but becomes green in color. As a rule, the organ be- 
comes fleshier with this appearance of the chlorophyll coloring matter. In 
the actual metamorphosis of the floral organs into leaves (phyllody, phyl- 



1 Kraus, C, Untersuchungen liber kiinstliche Herbeifiihrung- der Verlaubuiig 
usw. durch abnorme Drucksteigerung-. Forsch. auf. d. Geb. d. Agrikulturphysik. 
]S80, p. 32. 

2 Goebel, Beitrage zur Moiphologie und Physiologie des Blattes. Bot. Zeit. 
1880, p. 803. 



342 

lomorphosis) the organ also approaches the foliage leaf in form. Bracts 
become normal stem leaves, the sepals are replaced by actual foliage leaves, 
the petals become green and fleshy, the pistils become stamens (staminody) 
or the stamens and pistils assume the character of petals or green, fleshy 
leaf-like structures, as, for example, in the double cherry, the double 
Ranunculus, etc. In mignonette, through phyllody of the ovules, little leafy 
axes can be formed in the urn-like open ovule cases. In the favorite tub- 
erous Begonias, 1 found that the placentae had grown out of the ovule cases 
and the ovules carried over on to petal-like transformed branches of the 
pistil, etc. 

There are cases in which all the parts of a flower are transformed into 
small, uniformly green leaves, i. e., a complete green flozver condition 
(chloranthy) arises. One of the best examples of this is the green rose 
{Rosa chinensis, Jaqu.), received in its time with great enthusiasm, the 
transformation processes in which have been thoroughly described by 
Celakowsky\ 

I would like to introduce here also parthcnogensis, which various 
scientists have often proved recently to be of constant occurrence. Kirchner" 
saw in this an arrangement "which, differing from the much more wide- 
spread, spontaneous self-pollination, serves to assure the development of 
seed, capable of germination, in cases where, for any reason whatever 
pollination has become uncertain or difficult." Even those seed primordia 
can be assumed to be of a somatic character, in wdiich, at the time of the 
production of the embryo sacs, the reducing division is suppressed and the 
egg cell retains a vegetative character. 

In cryptogamic plants Apogamy corresponds to the process of phyllody 
in the phanerogams. Instead of the sexual products, vegetative organs 
appear here, as in Athyrium Filix fem'ma var. cristatum, Aspidium falcatum 
and Pteris cretica. It is said that in the last plant, no more female sexual 
organs are formed at all, but the young plant is produced from a vegetative 
sprout exactly on the places in the prothallium, where the archegonia m.ust 
have stood^. 

Such plants which "produce their young alive" (viviparous) furnish 
abundant material for propagation, just as, for example, the bulblets of 
many lilies, produced by the transformation of a flower. 

The Barrenness of the Hop. 

A special process of phyllody, of great agricultural significance, is the 
barrenness, the blindness, the fool's head formation of the hop. The names 
designate only dilTerent degrees of a malformation which begins with a 
simple, abnormal lengthening of the catkins and develops into the formation 

1 Celakowsky, Beitrage zur morphologischen Deutung- des Staubgefafses. 
Pringsheims Jahrb. 1878, p. 124. 

2 Kirchner, O., Parthenogenesis bei Bliitenpflanzen. Ber. d. Deutsch. Bot. Ges. 
1904, Vol. XXII. Generalversammlungsheft. Here also a bibliography. 

a Noll in Straszburger's Lehrbuch der Bot. 1894, p. 243. 



343 



of fluttering, dark green inflorescences on which develop foliage leaves, 
difl^ering in size and varying in numbers. 






Fig. 51. Different transitional stages between the normal hop catkin 
and a leafy one. (Orig-.) 

Hop growers know that the cjuality of the hop decreases according to 
the increased length of the catkin and enlargment of the bracts. The de- 
velopment of the catkins, most advantageous for technical use, is a short, 



344 

compact form of the whole inflorescence and a short, broad form and papery, 
thin consistency of the bracts, as shown in the preceding Fig. 51, Nos. i and 2. 
Half of the leaves have been removed in No, 2, in order to show the short- 
ness of the joints in the catkin spindle. Nos. j and 4 show the abnormal 
excessive lengthening of the catkin, known among growers by the name 
"hrausche" hops, which must count as the first stage of phyllody. Such 
"brausche" hops are coarse, contain less substance, ripen somewhat later and 
have more herbaceous bracts. Beginning with this condition, the phenom- 
ena of phyllody increase up to the stage shown in No. 5. The green foli- 
aceous leaves, which here become visible, attain at times the size of a nor- 
mal leaf, h is the leaf blade which may be followed back into the petiole. 
At the base of this petiole stand the two green lateral leaflets {n,n) which in 
the present basal part of the catkin are very small, but increase in size up- 
ward. No. 6 is taken higher up on the inflorescence and shows the lateral 
leaflets {n,n) in a size equal to the other bracts, while the leaf body {h) is 
much smaller. The remaining bracts and protective leaves are seen at No. 5. 
Each one encloses a flower. 

The scale leaves, which exceed developmentally the other leaves and 
are developed only in the normal female inflorescence of the hop have the 
same bract-like constitution as do the protective leaves, so that the whole 
catkin seems composed of uniformly developed bracts. All the bracts are 
short lived and soon become dry skinned, when they lie over one another 
like tiles. 

The barrenness consists, therefore, of the development of the otherwise 
suppressed leaf blade between every two bract-like leaves. Wide exper- 
ience now shows that damp years^ and soils strongly manured with sub- 
stances containing nitrogen cause the more extensive appearance of the 
barrenness. Frequent summer rains, resulting in cloudy days, are often 
injurious, even without directly producing the disease. The cells of the 
leaf, as well as the axis, then elongate and even if favorable harvest weather 
occurs, the catkins ripen only superficially. They are brought into the 
storage rooms while containing much more water of vegetation, thereby 
causing a very rapid heating of the whole heap. Consequently, even in well- 
developed catkins, a rapid loss of the peculiar gloss and the light green 
color takes place, together with a considerable reduction in value of the 
whole harvest product. 

As a remedy for the barrenness, the removal or checking of the causes 
must be attempted, in case these are found in the soil in the form of excess 
of water or nitrogen. If the cause is cloudy, damp air, all means should 
be utihzed which further the greatest possible aeration and illumination of 
the hop-plantation. If nitrogen is present in the soil in excess, a subsequent 
fertilization with superphosphate is advisable. 



1 Beobachtungen iiber die Kultur der Hopfenpflanze. Published by the Deut- 
«icher Hopfenbauverein, Jahrg. 1879-82. 



345 
Forked Growth of Vines. 

It may be noticed in various localities, that different varieties of vines 
assume a tendency to excessive branching and retain it hereditarily. The 
kind of false ramification appears as a forking of the vines and such dis- 
eased plants are usually little if at all productive. Rathay^ published the 
most thorough observations on this subject and corroborated these state- 
ments in lower Austria. The wine growers there, who call these branch- 
sick vines "Forks," or "Double tipped," state that the forked formation may 
commence in very different places. The vines which in adjacent 
groups usually begin showing this abnormal direction of growth, 
first develop scattered forked branches and in this way present a "spurious 
forking" as may be seen everywhere in luxuriant vineyards. This initial 
stage of the disease is not dangerous, since the plants frequently return to a 
normal growth. The danger begins with the spread of the disease over the 
whole plant. Correlated with this is the transmissibility of the disease. 
This has been demonstrated in cuttings and suckers of affected vines. 

No cause of this phenomenon can be given as yet with certainty. 
R.athay was convinced that parasites were not present. The opinions of 
practical workers disagree greatly. Some think that exhaustion of the soil 
by intensive grape culture is the cause, while others are of the opinion that 
a clogging of the soil due to heavy rain storms or to the working of the 
soil during and soon after rain has an injurious effect. 

In my opinion this disease is a phenomenon of turning green — vires- 
cence — i. e., a morbid increase of the vegetative development. 

Kaserer's- statements favor this hypothesis. He states that, the first 
evidences of the disease are found in the transformation of the covering 
bract of the tendrils into a small leaf, the most advanced stage in the trans- 
formation of all the tendrils into leafy shoots. In grape vines, the tendrils 
are axial organs, of which the development depends upon the amount and 
constitution of the organic building materials present. In younger vines 
they become herbaceous shoots, but in older ones develop into inflorescences 
at the lower buds. If all the tendrils are transformed into leafy shoots 
the vegetative development will predominate, a morbid condition. The 
building material present is wrongly utilized. The cell sap necessary for the 
formation of the sexual organs is not properly concentrated. Thus far it 
is possible to agree with Krasser', who speaks of a diseased condition of 
the protoplasm in certain regions as a cause of this "herbaceousness." 

If Krasser, referring to the works of Kober and Gaunersdorfer (1901) 
insists that no disturbances in conduction and no lack of nutritive sub- 
stances can be assumed as causes of the "herbaceousness," w^hich represents 

J Rathay, Emerich, tjber die in Nieder-Osterreich aJs "Gabler" oder "Zwiewip- 
fler" bekannten Reben. Klosterneuburg, 1883. 

2 Kaserer, H., tJber die sogenannte Gablerkrankheit des Weinstocks, Mitteil. 
d. k. k. chemiscli-physiol. Versuchsstation Klosterneuburg-, 1902. Part 6. ' 

3 Krasser, Fridolin, tJber eine eigentiimliche Erkrankung der Weinstocke. II, 
Jahresb. d. Ver. d. Vertreter d. ang-ewandten Botanik. 1905, p. 73. 



346 

only a metamorphosis of scattered buds into leaves, but that a very local 
affection of the cells of some buds is present, this does not upset at all 
our theory of phyllody. It is a matter of course that the formation of each 
organ takes place under definite nutritive conditions. That these change 
constantly and are the product of the momentary combination of all the 
factors of growth has been emphasized already in the introductory chapters 
of this edition. It is still far from possible to determine these combinations. 
For the present, we have only scattered observations on this subject, — that, 
for example, an excess of potassium and nitrogen in relation to the con- 
sumption of the other nutritive substances one-sidedly increases the vege- 
tative activity at the expense of the sexual development. An excess of 
water with a relatively scanty supply of light can in a similar way influence 
the direction of growth. We cannot determine how these disturbances in 
equilibrium are produced individually for the formation of each organ, 
whether momentary' arrestments in the absorption or transportation of the 
nutritive substances form the cause. 

We can, therefore, state only very generally that phyllody is produced 
by a preponderance of the direction of growth producing green leaves as 
against the mode of growth favoring the sexual organs. The so-called 
"changelings" or spurious f orkings, • are plants which are still partially 
fruitful. Among the conditions favoring the tendency to phyllody, Kaserer 
cites unfavorable positions on which drainage water collects from higher 
lying ground. Healthy plants set out in a group of affected plants are said 
to fork rapidly. Superphosphate seems to favor a return to fruitfulness. 

We consider the replacement of diseased plants by healthy ones of 
varieties which withstand a more abundant supply of water and heavier 
soils to be the most advisable mode of procedure. The so-called aggregations 
of forked plants might be improved by drainage and the addition of sand 
together with that of calcium phosphate. 

Falling of the Leaves. 

The falling of the leaves, the normal result of age^ is of pathological 
significance only because, under certain circumstances, it can appear 
prematurely. 

The causes which may lead to such premature dropping of organs 
are of different kinds, and extremes of weather may give rise to it. Ac- 
cordingly, the phenomena could be treated in different sections of this book. 
Nevertheless, we prefer to consider here the processes of loosening as a 
whole, because they are connected with changes in the tissues, in which in- 
creases of turgor occur decisively, after the organs, for any cause whatever, 
have become functionally weak. In regard to the falling of the leaves, for 
example, Wiesner- differentiates the falling of the leaves into a summer 



1 Dingier, H., Versuche und Gedanken zum herbstlichen LaubfalL Ber. d. 
Deutschen Bot. Ges. Vol. XXIII (1905), p. 463. 

2 Wiesner, Jul., Ber. d. Deutschen Bot. Ges. Vol. XXII (1904), p. 64, 316, 501. 
Vol. XXIII, p. 49. 



347 

falling, falling due to groivth, falling due to heat and falling due to frost. 
Pfeffer^ gives us an insight into the diversity of the causes. "Such a hasten- 
ing of the leaf-fall is brought about, for example, by insufficient illum- 
ination, also by an insufficient water provision and by too high a temperature. 
Not infrequently, however, a premature shedding of the leaves is caused 
especially by the sudden change of external conditions, which for perti- 
nent reasons concern fiirst of all the older leaves." As examples of the 
injurious influence of a sudden change in the amount of transpiration, 
Pfeffer cites the sudden loss of leaves in plants as soon as they are brought 
from the moist greenhouse air into a dry room. Sharp changes of temper- 
ature, illumination, etc., can act in the same way. 

V. Mohl- has studied the anatomical processes very thoroughly. 

The shedding of leaves is accomplished by the formation of a trans- 
verse parenchyma layer at the base of the petiole, as a rule within the leaf 
cushion, and, in fact, usually where the cork of the bark passes over into 
the epidermis of the petiole, and in the interior of the petiole tissue, which 
is produced by a special cell division. The cells of this layer separate from 
one another in one plane. 

V. Mohl calls the zone in which the layer of separation is formed, the 
"round-celled layer," because it consists of very short parenchymatous 
tissue, which toward the leaf body gradually passes over into the elongated 
cells of the petiole, but is sharply defined on the side toward the bark of 
the twig. 

In very many cases, a cork layer formed of plate-like cork cells, sep- 
arates the green bark of the branch, rich in chlorophyll and starch, from this 
short-celled parenchyma of the found-celled layer of the leaf cushion which 
usually contains no starch, and very little cholorophyll and turns brown 
at the base at the time of leaf fall. Schacht^ considers this cork sheet, 
which, at the sides, passes over into the inner cork layers of the bark, to be 
the cause of the shedding of the leaves. In fact, it may be assumed that if 
a cork layer be shoved in between the tissue of the bark and that of the 
petioles, the food supply of the leaf is impoverished and the leaf gradually 
goes to pieces. Nevertheless, the cork layer is not the cause of the leaf 
fall, for V. Mohl has shown that it is not formed in many plants which 
cast their leaves. Thus, for example, no cork layer can be found in ferns 
with deciduous fronds (Polypodium, Davallia) further, in Gingko biloba, 
Fagus silvatica, some varieties of oak, Ulmus campestris, Morus alba, Frax- 
inus excelsior, Syringa vulgaris, Atropa Belladonna, Liriodendron tulipifera, 
etc. On the other hand, the cork layer is formed in Populus canadensis and 
/'. dilotata, Alnus glutinosa, fuglans nigra. Daphne Mesereum, Sambucus 
racemosa. Viburnum Lantana, Lonicera alpigena, Vitis vinifera, Ampe- 
lopsis quinquefolia, Aesculus macrostachya, Pavia rubra and P. lutea, Acer 



1 Pfeffer, Pflanzenphysiologie. II Edition, Vol. 2 (1904), p. 278. 
-' V. Mohl, Tiber die anatomischen Veranderumgen des Blattgelenkes, welche 
das Abfallen der Blatter herbeifiihren. Bot. Zeit. 1860, Ncs. 1 and 2. 
•i Schacht, Anatomie and Physiologie, II, 136. 



348 

platanoides, Prunus Padus, Rohinia Pseudacacia. The cork layer should, 
therefore, be considered only as a protective layer for the bark tissue ex- 
posed by the falHng of the leaf, often developed before the leaf has fallen. 

The real layer of separation, in fact, is formed above the cork layer 
in the almost isodiametric parenchyma of the round-celled layer, not in the 
brown-walled portion bordering directly on the cork, but in the adjacent 
healthy portion, of which the walls are light colored. There, shortly before 
the leaves fall, a zone is found running obliquely in front of the bud toward 
the outer side of the petiole and composed of young, delicate walled cells with 
intercellular spaces containing less air. Small starch grains are found in 
these cells which otherwise do not occur in the enlarged end of the petiole. 
In this newly formed tissue-zone, the cells separate from one another with- 
out tearing, but by rounding ofif, as Inmann^ has observed. One part re- 
mains attached to the petiole as it breaks off, the other to the leaf scar 
Avhere it soon dries up. The leaf-fall, accordingly, is a vital act, not a me- 
chanical one. Before the leaf falls, vascular bundles take no part in the 
changes undergone by the cell tissue of the swollen end of the petiole. These 
extend through the round celled layer and the cork layer without changing 
their organization, even without turning brown. The cleavage in these 
*^^kes place in a purely mechanical way after the split has extended through 
the parenchymatous tissue. 

In many plants (Nuphar, many monocotyledons, herbaceous ferns- ) in 
which there is no cork formation on the leaf scar, its outer dried cell layers 
pass over directly into the healthy bark parenchyma and are thrown off 
during later development. 

V. Bretfeld^ arrives at the conclusion that the process of abscission of the 
leaves is the same in monocotyledons and dicotyledons, only the shutting off 
of the abscission surface differs in different genera. An essential difference 
lies, however, in the time of the formation of the tissue zone in which the 
separating layer is produced. While in dicotyledons, the process of ab- 
scission is the product of living activity, taking place shortly before the 
leaves fall, this process in the tree-like monocotyledons, orchids and 
Aroideae is exhibited' as an act prepared by the primordia of a definite 
layer and advancing with the general tissue diff"erentiation. 

The loss of leaves occurring in conservator)^ plants of the her- 
baceous and bushy Begonias, of Cistus species and many Mytaceae and 
Leguminoseae from New Holland must be mentioned in discussing leaf 
fall due to an excess of water. The upward force of the sap is increased 
excessively by an abundant watering of the plants at the time of minimal' leaf 
activity. The cleavage surfaces of the falling leaves at times are very 
mealy, due to the loosened cells of the abscission surface. 



1 Bot. Zeit. 1850, p. 198. 

2 V. Mohl, tJber den Vernarbungsprozess bei der Pflanze. Bot. Zeit. 1849, p. 645. 
p. 645. 

3 V. Bretfeld, tJber den Ablosung-sprozess saftig-er Pflanzenorgane Bot. Zeit. 
1860, p. 273. 



349 
Leaf Casting Diseases. 

The leaf casting diseases form the most significant case of premature 
dropping of the leaves. We speak here in the plural, although it is custo- 
mary generally to call a sudden dropping of the needles of young pines 
"leaf casting." All plants can "cast their leaves" which are capable 
in any way of pushing off their dying leaf apparatus. The only concern, 
then, is whether the leaf body in its entirety suddenly becomes functionally 
weakened, or even functionless. It is only because it appears so uncom- 
monly abundantly among pines and is accompanied by severe results that 
the dropping of the pine needles is cited especially often for "Leaf Casting." 

This form of disease manifests itself most frequently and severely in 
seedlings two to four years old, the needles of which suddenly become 
I'rownish-yellow or brownish-red in the spring and fall after a short time. 
The considerable spread of this phenomenon dates only from the general 
change in the cultural methods; instead of sowing the seed and of the 
Femel management, the raising of plants in seed beds has been introduced. 

Since that time it has been observed that in the months from March to 
Mav, often within a few days, great areas of seedling plants look as if they 
had been burned. In this, however, it can be noticed that young plants 
protected by a not xtry close conifer forest, or one of mixed trees, or, in 
nurseries protected by trees of an earlier seeding, do not cast their needles, 
while exposed areas in the open or in enclosed places are extraordinarily at- 
tacked by the disease. Specimens with pruned roots suffer more than those 
with long, vigorous ones, while plants on wet soil suffer most intensely. 
Mountain plantations are less attacked than those on plains and a northern 
exposure seems to be almost entirely spared, while a southern or western 
one suffers greatly. 

The disease does not appear every year, but generally only after wet, 
cold winters with but little snow, and alternating sharp frosts. The plants 
cast their needles most extensively if dry springs, March and April, are 
distinguished by bright warm days followed by cold nights. Often the 
phenomenon occurs in stripes or spots. It has been observ'ed further, that 
plants protected from the noonday sun by neighboring woods, etc., general- 
ly did not become diseased. Plants in seed beds, which were left covered 
until after the time of spring frosts, did not cast their needles while ad- 
jacent, unprotected seedlings did so. Seedlings grown between older 
covered plants or between broom plants, even those protected by high grass, 
did not develop the disease, while others where the broom plants had been 
dug out in the spring were attacked. 

Ebermayer\ in explanation of these facts, states that observations of a 
forestr}' experimental station, made for several years, showed that in March 
and April the soil temperature down to ij4 rneters was scarcely more than 



1 Ebermayer, Die physikalischen Einwirkungen des Waldes auf Luft und 
Boden etc. Resultate der forstl. Versuchsstat. in Bayern. Aschaffenburg-, 1873. 
Vol. I, p. 251. 



350 

5 degrees C, while the air temperature in the shade not infrequently was 
higher than 19 to 22 degrees C. Such differences in temperature between 
the air and the soil result directly in the excessive transpiration of the aerial 
parts of the plant, while the roots kept in a state of inactivity because of the 
cold soil, are incapable of taking up the soil water, or not to the amount 
necessary to replace the aerial loss. Thus the young pines dry up even 
when the soil is abundantly wet. 

The greater the difference between the soil and the air temperatures in 
direct sunlight, the more abundant and devastating is the leaf casting. On 
the other hand, the more frequently conditions arise which raise the soil 
temperature, such as warm spring rains, or which prevent a greater lowering 
of it, i. e. masses of long unmelted snow or of mulch, the less the disease 
appears. This lessening of the disease will take place also if the temper- 
ature of the air and the intensity of the sunlight are decreased as, for ex- 
ample, by a very cloudy sky, by a position on northern slopes, or under 
the protection of larger trees, high grasses or bushes, or by the artificial 
screening of the seed beds during the day. 

That older plants suffer less often from leaf casting is explained, in the 
first place, by the more strongly developed wood which in all plants may be 
considered as a water reservoir; in the second place, by a more abundantly 
developed, deeper reaching root system, which possesses more organs for 
absorption in its greater number of fibrous roots. 

Holzner^ has raised an objection to this theory. In leaf casting, dis- 
coloration appears within 2 to 3 days, while, in an actual process of dr)'ing, 
the pine needles redden only gradually. He considers the cause a direct 
effect of frost. It is a well established fact that frost will also cause leaf 
casting. Baudisch- protected seedlings by a brush covering one meter deep 
above the surface of the soil. The plants which had remained healthy until 
the protection had been removed then suffered from the April frosts. 

Many authors ascribe an injurious influence to autumn frosts^. The 
theory most generally accepted at present considers the disease to be para- 
sitic and, accordingly, recommends that it be treated with fungicides. Ac- 
cording to V. Tubeuf's* experiments, it cannot be doubted that there are 
also cases of parasitic leaf casting^. However, the fact must be taken 
into consideration, that the fungi of leaf casting are present in abundance 
on older pines, firs, spruces and larches, without calling forth the specific 
phenomena. Therefore, unless some conditions especially favorable for the 
much dreaded juvenile disease are present, it cannot become epidemic. 



1 Holzner, Georg. Die Beobachtung-en iiber die Schtitte der Kiefer oder Fohre 
und die Winterfarbung- immergriiner Gewachse. Freising, 1877. Here bibliography 
of 145 studies on leaf casting. 

2 Centralbl. f. d. ges. Forstwesen VII, 1S81, p. 362. 

3 Alers in Centralbl. f. d. ges. Forstw. 1878, p. 132. Nordlinger ibid p. 389. 
Dammes and others, Jahrbuch d. schles. Forstvereins 1878, p. 40 ff. 

4 V. Tubeuf, Studien uber die Schlittekrankheit der Kiefer. Arb. d. Biolog. Abt. 
am Kais. Gesundheitsamt. Part II, 1901. 

5 Cf. Vol. II, p. 268. 



351 

All these statements as to the factors causing leaf casting agree in 
maintaining that the needles fall because they have become weakened 
functionally or still are normally weak as a result of the winter's rest.. 
Moreover, the abscission process depends upon the development of the cleav- 
age layer which presupposes living activity and an increased turgor. Thus, 
there arises an antagonism; the leaf organ is not at the time in a condition 
to function as a normal center of attraction and consumption. Because of 
its anatomical structure the basal part above the region of the subsequent 
cleavage can be excited and it is prematurely brought to the development 
of this cleavage layer by the increase in turgor, which arises in the spring 
due to exposure to the sun, or has been retained from the previous year, 
and finds no equalizaion since even the inactive lamina of the leaf do not 
take up the water from it. This disturbance in the equilibrium of the turgor 
distribution is the cause of all premature dropping of the leaves. 

In the special case of the pine leaf casting I think that the contrasts 
described by Ebermayer and, indeed, the sharp contrasts, represent the 
most frequent cause of the disease. Only in explaining it, I differ from him 
in so far that I accept as cause the winter's inactivity, evident also in the 
constitution of the chloroplasts, instead of the excessively increased evap- 
oration from the needles. Only the base of the needle is excited and de- 
velops the cleavage layer, which, as will be mentioned under petals, can, 
under certain circumstances, be produced in an extremely short time. I am 
of the opinion that the needle does not become dried out, but is put out of 
action by the cleavage layer. I would like to assume from the absolute 
scanty elimination of water by pines in winter, that a drying of the needles 
resulting from an excessively increased evaporation, is not the cause of the 
discoloration and falling of the needles. An experiment in a water culture 
of one year old seedlings showed me that a pine ceased its evaporation on 
the i/th of November despite following days with temperatures of + 3> 4. 7> 
9 degrees C. Up to the 22nd of December they did not evaporate one gram 
more of water, although the root stood in water\ It can, therefore, scarcely 
be assumed that the spring temperature can, in a few days, cause a great loss 
of moisture, more particularly as the pine is a tree species which evap- 
orates the least of all-. 

Since the drying of the needles does not seem to me to be the cause of 
leaf casting, but rather a lack of equallization in the water supply, resulting 
from the sharp contrast between the needle surface, weakly assimilative, 
and its base, already active, I would like to believe the best preventative 
method to be the avoidance of such sharp contrasts: I, therefore, add the 
proposals made by Ebermayer : — 

A. Increase in soil temperature : ( i ) due to the prevention of too great 
cooling during the winter by means of leaf, brush or moss coverings; (2) 



1 Sorauer, Studien iiber Verdunstung. Forschungen auf d. Gebiete der Agri- 
;ulturphysik, Vol. Ill, Parts 4,& 5, p. 10. 
- V. Hohnel, loc. cit. Vol. II, p. 411, 



352 

by draining wet soils; (3) by loosening and mixing heavy soils with earths 
rich in humus, so that the warmth of the air can penetrate more easily. 

B. Lessening of sharp contrasts by shading: (i) by brushing the seed 
beds with evergreen boughs, which should not be removed on warm days ; 
(2) by making the seed beds in places which are protected on the south by 
tracts of trees. 

"In the restoration of pine woods, on the wliole, the most radical means 
consists in a return from the extensive clearing system to a plan of seeding, 
such that the young plants have the necessary protection from the direct 
sunlight in the overhead wood protection, but can still obtain as much light 
as is necessary for their vigorous development. The same end is attained 
by a slender fringe of trees running from N. E. to S. W., which are much 
used at present in the restoration of the pine tracts. In the cultivation of 
extensive clearings the shading can be obtained by a shelter growth of such 
plants as are favored by the habitat, — for example, by birches, etc., or by 
previous spruce plantations." 

"In cases, where no shelter growth can be arranged because of 
local conditions, the planting of seedlings is preferable (yearling plants with 
a good root system seem best suited for this), yet the first two cultural 
methods will much more surely attain the desired goal." 

Finally it is well to emphasize that every attention should be given to 
obtaining a good root system ; — accordingly, too thick seeding, heavy, un- 
broken soil, considerable injury in transplanting and the like are to be 
avoided. 

A leaf casting occurs also in older trees. The older needle bunches of 
plants standing on moor-soils in misty depressions, or found in localities 
subject to extreme frost, fall prematurely. But, in the autumn, these hang 
to the trees, turning yellow or drying up, and are thus distinguished from 
the seedlings specifically diseased with leaf casting. On heavy soils the 
pine always dies easily^. 

Leaf-Fall in House Plants. 

Among the most delicate of the house plants belong the azaleas, be- 
cause, as a rule, they suddenly drop their leaves in summer or in the 
autumn; the broom-like little tree then at best develops only a few pitiful 
flowers. Here too are concerned sharp contrasts occurring suddenly. Either 
the plants (usually set in moor soil) in summer are left too dry, and later 
watered very abundantly, or they are brought too suddenly into the warm 
house in the autumn. In both cases, the leaves are weak functionally and 
then their functioning is increasingly stimulated by the increased upward 
pressure of the water. If the transition is brought about gradually, the inac- 
tive leaf surfaces would have time to resume their normal action by a general 
slow increase in their turgidity and there would be no resultant injur}\ 



1 Runnebaum, A.. Das Absterben und die Bewirtschaftungr der Kiefer im Stan- 
g-enholzalter usw. Zeitschr. f. Forst- u. Jag-dwesen, 1892, p. 43. 



353 

But, with the sudden upward pressure of the water, the basal region alone is 
stimulated, thus causing the development of the cleavage layer. 

In foliage Begonias, rubber plants, camelias and many others, the 
leaves begin to drop in .the autumn and winter. Here, the leaf is in a 
natural, dormant state. Abundant watering in a warm room causes an up- 
ward current of water which the leaves cannot utilize. 

Here are briefly a few of my own observations. A Begonia fuchsioi- 
des which had been forced through the winter in a warmer room, was 
brought at the end of March into an unheated, but sunny room. Within a few 
days it dropped all its leaves except the youngest ones. Libonia floribunda, 
which had been kept very cold, was suddenly brought into a greenhouse in 
December for forcing. The plants dropped all the older leaves, while 
plants remaining in the cold retained theirs. Some specimens of a double 
white fuchsia were brought into the house in the autumn in order to get 
early shoots for cuttings. Other specimens of the same variety were left 
in the cellar until the beginning of March. At this time the tips of all the 
plants were set as cuttings in a bench with 25 degrees C. soil heat. After a few 
days the cuttings, from the plants in the cellar, lost their leaves up to the 
very tips, while the others had not even lost the leaf at the cut surface. The 
tips of one branch, taken a few days later from a cellar plant, were placed 
in sand in the cellar, without any especial care and were found in May to 
have rooted, while the tips from the cellar plants had gone to pieces in the 
warm case. 

For house plants it may be recommended as a fundamental principle 
that the plants should be subjected gradually to other vegetative conditions, 
and the dormant period, upon which every vegetative plant enters, should 
not be interrupted by an increase in the supply of heat and moisture. 

The Dropping of the Flowering Organs. 

This process takes place in the same way as that of the leaves^ The 
composite axes of the inflorescences in Aesculus and Pavia are known to 
separate into their individual parts, which loosen from one another with 
smooth cleavage surfaces. In the same way, if many fruits are set, a num- 
ber of half-grown ones are often abscissed to a joint in the fruit stem. 
The staminate blossoms of the Cucurbitaceae are abscissed at the cleavage 
layer formed on the boundary between pedicel and blossom, those of 
Ricinus communis in a line of separation, produced at a joint lying in the 
lower part of the peduncle. The hermaphrodite blossoms of Hemerocallis 
fidva and H. flava, left unfertilized, are abscissed by a cleavage layer ex- 
tending under the base of the blossom through the upper part of the ped- 
uncle. The cells of the cleavage surface round up and separate from one 
another. 



1 V. Mohl, H., tjber den Ablosung-sprozess saftiger Pflanzenorffane Bot. Zeit. 1860, 
p. 273. 



354 

In the same way a fully developed cleavage layer is found in the sepals 
of Papavcr somniferum, Liriodendron tulipifera, at the time they fall; in 
the falling parts of the calyx of Mirabilis Jalapa, Datura Stramonium; in 
the petals of Rosa canina, Papaver; in the single corolla of Lonicera Capri- 
folium, Rhododendron ponticum, Datura Stramonium; in the stamens of 
Lilium bulbiferum and L. IMartagon, Dictamnus Fraxinella, Liriodendron ; 
in the stigma of Lonicera Caprifolium, Mirabilis Jalapa and Lilium 
Martagon. 

In the majority of cases, the cells of the abscission layer contain no 
starch, or at least no more than does the surrounding tissue, while, in the 
leaves and thick sepals and petals of Liriodendron abundant starch is pres- 
ent. This lack of reserve nutriment is explained by the rapid formation of 
the cleavage layer in the blossoms, for which the momentarily transportable 
nutritive substance is sufficient. In the sepals of Papaver somniferum, the 
cleavage layer is produced in a single night, in the petals of single roses, 
in the hours of an afternoon. While cell increase seems to occur in the 
cleavage layer of leaves, it can hardly take place in the petals. The pro- 
cesses there visible consist only of a more abundant protoplasm, an in- 
creased porosity and mutual separation, due to a rounding up of the cells, 
and, at times, a pouch-like enlargement of the cells, whereby the cleavage 
layer looks velvety. The appearance of the cleavage layer is delayed as the 
organs are better nourished. 

The Shelling of the Grape Blossom. 

By the term "shelling" or "falling" the winegrower means the dropping 
of blossoms soon after blooming. In some regions the phenomenon returns 
annually while, in other localities, it appears only in isolated years, as, for 
example, in those when wet, cold weather destroys the blossoms. Accord- 
ing to Miiller-Thurgau's^ investigations, with a low temperature at the 
time of blossoming, the cells of the stigmas were beginning to turn brown 
even before the blossom sheaths fell, which indicated death or at least 
an extensive retarding of the process of pollination. Actually, on such 
stigmas the pollen grains did not develop pollen tubes at all, or only 
poorly. The dropping of the petal cap took place \Qvy slowly or was en- 
tirely suppressed. The ovule cases of such blossoms remained for some 
lime, often actually for a long time, but they scarcely enlarged at all. How- 
ever, since, according to Miiller's discoveries, ringing of the vines is usually 
beneficial, the low temperature cannot be the direct cause of the incompleted 
act of pollination and the failure to mature the seed. The dull, cool weather 
during blossoming is especially favorable for the growth of leafy shoots, 
which, on this account, require the material stored up for the development 
of the inflorescence, so that the nutrition is not sufficient for the blossoms. 
Such a starving of the blossom cluster and, consecjuently, a more or less 



1 Miiller-Thurgau, tJber das Abfallen der Rebenbliiten und die Entstehung 
kernloser Traubenbeeren. Der Weinbau, 1883, No. 22. 



355 

extensive shelling of the blossoms will occur also with weather favorable 
for blooming, if abundant nitrogen is present in the soil, or if virgin soil 
with an abundant supply of nutrients and water is used for the cultivation 
of grapes, when the luxuriant development of the vegetative organs limits 
the further development of the sexual apparatus. 

In fact, Miiller gives examples of such cases and, at the same time, 
states his experience, viz., that sometimes fertilization has helped over- 
come the evil, and sometimes a long incision in the vine accomplishes the 
same end. 

Miiller also ascribes to the same causes the appearance of seedless 
grapes on the bunch, which, as a rule, is correlative with a partial shelling. 
The seedless grapes are larger than the unpoUinated seeded ones which, at 
times, remain on the bunch even until autumn. The seedless ones, however, 
are not as large as normal, seed bearing grapes, although, like them, they 
color and become sweet. Indeed, it is evident that they ripen earlier and 
become sweeter than the grapes with matured seeds. 

Since the seed primordia in the seedless grapes do not seem much 
larger than at the time of blossoming, it must be assumed that some dis- 
turbance had taken place at that time. It is probable that, in such cases, 
pollinization had taken place, but that either a temporary lack of suit- 
able nutritive substances, or some other disturbance, prevented the further 
development of the tgg cell. The stimulus, exercised by pollination on the 
walls of the ovule cases is present and the grape consequently develops. 
Since, however, it does not need to use up any of the nutritive substances 
flowing towards it in maturing the seeds, this grape at first exceeds develop- 
mentally the grapes containing seeds. Weighing seedless and seeded grapes 
proves that the seed, in maturing, functions as a centre of attraction for 
material. Miiller-Thurgau^ found that the weight of the fruit flesh of lOO 
berries of Riesling was 

Seedless With i Seed With 2 Seeds Normal, with 4 Seeds 
25.0 g 58.2 g 77.2 g 112. g 

As examples of the differences in the material development, the results 
of an experiment by Miiller with Riesling may be cited here. 
1000 berries on the 25th of September showed 

Seedless a weight of 208.9 ?,> sugar 10.63%, acid 18.2% 

Containing seeds ...a weight of 846.0 g, sugar (^.77%, acid 24.2% 

On the 1 2th of October 

Seedless a weight of 231.0 g, sugar 14.7%, acid 11.0% 

Containing seeds ....a weight of 898.7 g, sugar 12.3%, acid 15.7% 

In regard to the effect of ringing, an experiment showed that the non- 
ringed vines bore only unfertilized grapes, which fell soon, while the bear- 



1 Mliller-Thurg-au, Einfliiss der Kerne auf die Ausbilding des Fruchtfleisches bei 
Traubenbeeren iind Kernobst. II. Jahresbericht d. Versuchs-stat. Wadensweil. 
Zurich, 1893, p. 52. 



3S6 

ing vines, which were ringed shortly before blossoming, furnished com- 
paratively long bunches with an extremely large number of seedless berries, 
between which were found only scattered normal ones. 

This formation of seedless grapes is a great injury, under our present 
conditions, since the prematurely ripe grapes shrivel before the general 
vintage until all the juice is lost, and drop off or decay; they, therefore, are 
wasted. If, on the other hand, this degeneration is increased, it may be 
termed an advantage. Probably our currants and Sultana raisins, among 
which only scattered berries with seeds are found, are the products of 
plants in which a seedless condition of the berries has become the rule. 
In other localities, cuttings of the currant grape are said to bear grapes 
with seeds. 

Eger^ gives some advice well worth considering. He studied the in- 
dividuality of different varieties of grapes from many points of view and 
found that certain plants of the same variety always ripen their berries 
earlier and that many, under otherwise similar conditions, show a lesser 
tendency to the falling of the bloom, which, especially in Riesling, is very 
considerable. Accordingly, in each nursery and vineyard those individuals 
should be labelled which are notable each year because of their favorable 
development, and only from these should cuttings be chosen for propagation. 

Other processes are found in our stone fruit trees when grown for 
trade. If the wood is thinned too much, i.e. too many leaf branches are 
cut away, in order to furnish light for the blossoms and young fruit, the 
buds, blossoms and young fruit may be dropped. By the sudden decrease 
of the evaporating leaf surfaces, an increased root pressure sets in for the 
other organs, which cannot take up the increased amount of water. Cleav- 
age of the abscission layer results. The dropping of the organs can natural- 
ly be initiated by other causes^. 

The Shedding of the Young Flower Clusters of Hyacinths. 

Many shipments of hyacinth bulbs from different growers have shown 
me that the shedding of complete but undeveloped flower clusters is not of 
rare occurrence. The uncolored, otherwise perfectly healthy flower clusters, 
still rather short, may be lifted from entirely healthy bulbs with fully de- 
veloped, often excessively elongated foliage. In the very luxuriant variety 
Baron Van Thuyll (originated in Holland) I found yellowish areas on 
otherwise normally developed leaves and these areas were shghtly swollen, 
even split here and there. The flower clusters were strong, perfectly 
healthy, perhaps 8 cm. in length, with an equally long, perfectly healthy, 
almost colorless stalk. 

The stalk had separated from the base of the bulb and the cells of the 
former were found to be swelled up more or less ascus-hke. This swelling 



1 Eger, E., Untersuchungen liber die Methoden der Schadling-sbekampfung 
und iiber neue Vorschlage zu Kulturmafsreg-eln fiir den Weinbau, Berlin, P. Parey, 
1905, p. 63. 

■■i The Dropping- of the Buds of Peaches. Gard. Chron. XIII, 1893, p. 574. 



357 

could be traced back from the place of cleavage, to varying depths. The 
pro-cambial cells of the firo-vascular bundles were broadened like 
bladders. 

The ducts thus exposed were simply broken off and, like the other ex- 
posed surfaces, had absolutely uncolored walls at first. 

The separation begins to show itself in the rounding up and bending 
outward of scattered cells in the basal tissue of the flower stalk, usually at 
a short distance from the base of the bulb. Simultaneous with the begin- 
ning of this convexity a swelling of the membranes of these cells appears 
at the side where the curvature sets in. It is the striated middle lamella of 
the cell walls which swells. Also, the swelling does not take place uni- 
formly in the whole membranous layer, but in some places to a greater de- 
gree than in others, hence the swollen, stripe-like areas have a knotted 
course, in places showing constrictions, 

A bead-like irregular condition of the outer surface of the cell walls 
in the cells lying next the cleavage surface seems worthy of attention. The 
hemispherical, to nipple-shaped swellings correspond to those in the woolly 
stripes in the apple core and take on a pure golden yellow color with chlo- 
riodid of zinc while the rest of the membrane becomes intensely blue. This 
disturbance sets in if, when growth starts, the hyacinths bulbs are given 
at first too great warmth and too copious watering. The flower cluster, 
not yet beginning to elongate, cannot utilize or absorb the water brought to 
it by the increased root pressure. Thus an excess of water is accumulated 
at the base of the flower stalk, whose cells elongate and weaken their 
connection. 

A slower forcing of the hyacinth might prevent this condition. 

Twig Abscission. 

The small branches which, usually, together with their fully developed 
foliage, are cut off from the main axis by some organic process may be 
called abscissed twigs. This abscission takes place chiefly in the autumn, 
yet it has been observed in summer (July) and as in leaf casting we 
must take into consideration diff'erent causes for the same phenomenon. 
All trees do not show this peculiarity and even those in which it appears 
do not shed their branches every year\ nor do all of them do so. Young, 
vigorous trees often do not shed, while older specimens, or those standing 
on poor soil, in the autumn cover the ground underneath them with branches. 

The poplars- furnish the best known example. Their branches, often 
meters long, with their swollen, hemispherically rounded joint-like abscission 
surfaces, smooth and shining like velvet in damp weather, show most clearly 
that the branch is not loosened by a forcible tearing of its component parts, 
but by a separation of certain tissue zones preceded by internal organic 
processes. 



1 Borkhausen, Forstbotanik I, p. 294. 

2 K. Muller, Hal., Der Pflanzenstaat, p. 532, gives an illustration of this. 



358 

The abscissed branches of oaks^ should be mentioned. In spruces 
except for the twigs frequently found bitten off by squirrels", there are 
probably no actual abscissed twigs. 

Further, this phyllocladia, or loosening of the branches, has been ob- 
served in Xylophylla and Phyllocladus^, in all Dammara species and 
especially in Dammara aiistralis, according to A. Braun, in several Podo- 
carpus species, in Guajaceae, Piperaceae, many bushy Acanthaceae, in 
Laurus Camphora, Crassiila arborescens, Portulacaria afra, Taxodium 
disiichum^ , in Tilia"' in Uhnits pendula, Evonymus, Primus Padus, Erica, 
Salix^, etc. 

The trees partially owe their characteristic habit of growth to these 
abscissed twigs. But the process of freeing varies according to the habitat, 
weather and other agencies. Thus Rose, for example, emphasizes that, 
with continued drought, the branches fall more abundantly; in the majority 
of cases, side shoots are dropped, but many plants lose their tips as well. 
The last case is observed most frequently in young trees grown on fertile 
soil. Nordlinger*' emphasizes that predominantly the weakly grown 
branches are the ones shed. 

Just as we find the leaves falling in summer, we also find a summer 
abscission of the branches. Gymnocladus, Catalpa bignonioides, Gleditschia, 
Tilia and especially Ailanthus glandidosa exhibit the same formation of an 
abscission layer and the separation of the cells from one another as found 
in the case of fallen leaves. In young shoots of Ailanthus it may be ob- 
served that, besides the parenchyma, even the still unlignified cells of the 
vascular bundles are involved in the formation of the cleavage layer. No 
cork is developed at this time either near the abscission or in the upper 
surface of the bark of the branch. Hence we often find it affirmed that the 
process of abscission does not depend upon the formation of a cork layer 
and that this cork layer is to be considered only as a protective layer for 
the free-lying parenchyma appearing sometimes earlier (before the cleav- 
age), sometimes later. 

We owe very extensive investigations of twig abscission to v. Hohnel', 
who has included conifers especially in the scope of his work, and has come 
to the conclusion that, in them, one cannot speak of any twig abscission. 



1 Th. Hartig, Naturgeschichte d. Forstl. Kulturpflanzen, p. 119. Pfeil, Deutsche 
Holzzucht, 1860, p. 136. Wigand, Der Baum, 1854, p. 67. Schacht, Der Baum, 1853, 
p. 305. Lehrbuch d. Anatomie usw., 1859, II, p. 19. 

2 Ratzeburg, Waldverderbnis, I, 1866, p. 219 (Plate 2S, Fig. 3). Compare Beling 
and further Roth (tJber Abspriinge bei Fichten), Bot. Jahresbericht von Just, II, 
p. 968, 971, and v. Hohnel, Bot. Jahresb. VI, Gonnermann, tJber die Abbisse der 
Tannen and Fichten. Bot. Zeit. von v. Mohl and Schlechtendal, 1865, No. 34. Rosei 
Bot. Zeit. 1865, No. 41. 

■i V. Mohl, tJber den Ablosungsprozess saftiger Pflanzenorgane Bot. Zeit. 1S60, 
p. 274 and 275. 

4 Rose, tJber die "Abspriinge" der Baume. Bot. Zeit. 1865, p. 109 (No. 14). 

^' V. Mohl, Dber den Ablosungs]>rozess saftiger Pflanzenorgane Bot. Zeit. 1860, 
p. 274 and 275. 

•! Nordlinger, Deutsche Forstbotanik. 1874, I, p. 199. 

"• V. Hohnel, tJber den Ablosungsvorgang der Zweige einiger Holzgewachse und 
seine anatomischen Ursachen. Mitteilungen aus dem forstlichen Versuchswesen 
Oesterreichs von v. Seckendorff, III, 1878, p. 255. Weitere Untersuchungen liber den 
Ablosungsvorgang von verholzten Zweigen. Bot. Centralbl. 1880, p. 177. 



359 

so long as the shedding of Hving, fresh and sappy branches is meant by it. 
In conifers, the branch to be shed first dies on the trunk, becoming yellow 
or brown ; it is shed in the usual way only after death, and a cork layer is 
always formed ; in this process, the wood breaks off at a definite place. 
The abscissed twigs of deciduous trees are shed in a living and sappy con- 
dition by means of a parenchyma zone traversing the thick wood but with- 
out the assistance of a cork layer. 

The age of normally abscissed twigs varies greatly. In Taxodium they 
are always one year old ; in Pinus strobus, always three years old ; in Piniis 
Larcicio, 2 to 7 year old ; in Pinus sihestris, 2 to 6 years old ; in Thuja 
occidentalis, 3 to 1 1 years old. It was stated at the outset that spruces and 
firs are said not to shed their branches. Nevertheless, I remember once 
having seen fresh spruce shoots with a dismembered surface resembling 
an articulation. 

In deciduous trees, it can be seen clearly that the twigs usually shed 
are those grown from lateral buds or adventitious eyes which are often 
weakly, and have grown only to short shoots. Only in poplars and willows 
and seldom in oaks are long shoots abundantly shed, and then only older 
ones (branches up to 6 years old). In rare cases the process is observed 
also in Primus Padus and Evonymus europaea, while in other trees usually 
one year old shoots alone are shed. 

Worthy of our attention is v. Hohnel's observation that the wood of 
Thuja occidentalis is weaker where the constriction will appear later, than 
at any other place. At the place which will later be the cleavage surface, 
ihe wood is greatly constricted. The parenchyma cells of the bark enlarge 
so that a considerable loosening is produced. In Thuja orientalis the fleshy 
branch cushion is lacking, and no regular shedding is found. Meehan^ 
found in Ampelopsis quinque folia that the basal internode remains stationary 
and, in the following year, produces new shoots, which in turn disarticulate 
with the occurrence of colder weather. 

The law formulated for leaf casting may be applied to abscissed 
twigs: — the centre of consumption, which here is the twig, for some reason, 
no longer forms' the normal centre of attraction for the undiminished flow 
of water and an excess of water accumulates accordingly in the basal zone 
which is still capable of reaction, and anatomically dift'erently constructed. 
Either the branches, from the beginning, have been more weakly set, or, 
because of an unfavorable habitat they do not develop so far or, in great 
summer drought, they have become prematurely ripe or they are rendered 
incapable of action by cold, etc. In a weak organ, the relative excess of 
water makes itself felt first at the base. If this organ develops, from the 
start, with the presence of a large water supply, no shedding takes place. 
Wet years exhibit little if any twig abscission. The theory held by fores- 
ters, that years with much twig abscission initiate good seed years, has its 



1 Meehan, On disarticulating branches in Ampelopsis. From "Proceed, of the 
Americ. Acad, of Philadelphia." Part I, 1880, im Bot. Centralbl, 1880, p. 1005. 



36o 

foundation in the fact that these are dry years, favoring the maturing of the 
blossom buds. 

Even if twig abscission is of Uttle practical importance in forestry, 
it is, however, of horticultural importance as a symptom. Especially in 
the autumn the stem parts of many greenhouse plants are abscissed, as in 
the bushy Begonias, Melastomaceae, Acanthaceae, etc. They are positive 
indications of excess of water, and the only means of prevention is to keep 
the plants dry, 

b. Increase of Food Concentration. 

Among the phenomena of disease to be discussed in this section, those 
must be considered in which an excess of water in the plant becomes mani- 
fest locally. In this the root activity is not necessarily increased, the accum- 
ulation of water is produced rather by a depression of the transpiratory 
activity of the leaves. Increase in turgor must set in in various organs, or 
parts of organs, by increased water supply, as has been proved artificially in 
severed leaves. Consequently, the fact remains to be considered here that 
the humidity of the air often co-operates decisively. Conversely, in other 
cases, in which an excess of nutrients is involved, attention should be called 
to the fact that this excess does not always presuppose an absolute accum- 
ulation in the soil, but also occurs when the solvent, i. e., the water, is 
temporarily present in too small an amount, thereby producing an injuriously 
high concentration of the soil solution. 

The demands made upon the soil solution by each species seem to differ 
according to the different quantitative proportions in which the various 
nutrients and other factors of growth participate in the production of one 
gram of dry weight of a species. In plants, for example, which require 
much potassium or nitrogen to produce their substance, a high percentage 
solution of these substances will be necessary for the root. The plants do 
not die, if the desired high concentration is not afforded them, but they 
change their mode of growth. They then require, as already proved, much 
more water just as if they must strive to obtain the necessary quantity of 
a certain nutrient by an increased absorption of the more dilute solution. 
In spite of the large quantity of water and substances otherwise offered, 
the production as a whole is small. A similar cessation of growth is found, 
if the plants are placed in a too concentrated soil solution. The absorption 
of water is relatively scanty; the amount of ash, however, large and the 
production in dry weight small. The excess then is taken up but not uti- 
lized, the mineral substances are simply deposited in the plant and may 
partially be leached out again by water. In water cultures with a high 
concentration of nutrients the short, gnarled root hairs are sometimes per- 
ceptibly covered with crystalline scales. Thus, for example, accumulations 
of saltpetre may take place in the plant if an excess of potassium nitrate is 
given. Emmerling^, by means of experiments, explains very acceptably 

1 Emmerling, A., Beitrage zur Kenntnis der chemischen Vorgange in der 
Pflanze. Landwirtsch. Versuchsstationen, Vol. XXX, Part 2, 1884, p. 109. 



36i 

the processes taking place. He shows that, exactly as with the use of cal- 
cium nitrate, potassium nitrate is decomposed by oxalic acid, even in very 
dilute solutions, in such a way that potassium oxalate and free nitric acid 
are produced, while oxalic acid does not act strongly on calcium carbonate, 
since it only coats it with an impervious, thin layer of calcium oxalate. If 
now the saltpetre in the soil is relatively great in proportion to the acid 
which a plant species can form, the saltpetre will be taken up, to be sure, 
but will be decomposed only proportionately to the oxalic acid present, and 
the free nitric acid is used in the formation of the proteins; the remaining 
saltpetre is deposited unchanged in the plant. 

In our cultivated plants the law certainly holds good, that they all re- 
quire the same nutrients but in different concentrations, and also that their 
capacity for enduring the accumulation of various substances is decisive 
for the success of the cultures. It should not be forgotten here, that neither 
the absolute amount of nutrients, which is borne without any injury, nor 
also the quantity of any nutrient proved to be the best (optimum) for pro- 
duction, represents absolutely fixed amounts for any definite plant. Rather, 
it should be assumed that the need for any definite nutrient changes con- 
stantly according to the combination in which the other vegetative factors 
are present at the moment. Thus, there is always a relative optimum and 
maximum for each vegetative factor. The mode of production and the 
product, — viz., the plant body, — change according to the momentary com- 
bination of the vegetative factors ; — thus morphological, anatomical, and 
chemical analyses give different values for each individual. 

Each change in concentration in the same nutrient mixture changes the 
method of growth and directly manifests itself, under certain circumstances, 
in the behavior of the root hairs, as stated by Stieler^ He found in the 
growing root hair, with each change in the solution, a change (thickening) 
of the membrane at the end of the root hair; — under certain circumstances, 
in fact, a cessation of growth occurs. In aqueous solutions of the electro- 
lytes, the root hairs in many plants form vesicular, irregular widenings, and 
can even crack open at the tip or (rarely) laterally. The non-electrolytes 
exercise an injurious influence, only if they have a poisonous effect or are 
present in too high a concentration, which causes plasmolysis. The ob- 
servation that concentrated magnesium compounds can be proved to act 
directly poisonously, is especially noteworthy. This cannot be observed 
for other nutritive salts even with high concentration. 

These investigations confirm my own observations, viz., that, in a 
highly concentrated nutrient solution, "gnarled or distended" root hairs 
appear, and thereby indicate that the plant has had to combat difficulties in 
absorbing its food. 

In regard to varieties of grain, the experiments indicate that oats, for 
example, can suffer from the amounts of nutrients which, for wheat, make 



1 Stieler, G., Uber das Verhalten der Wurzelharchen gegen Losungen Disser- 
tation. Kiel 1903. Cit. Bot. Centralbl. v. Lotsy 1904, No. 47, p. 541. 



362 

possible only a full production. Thus oats often fail on parcels of land, 
which have gradually been too heavily fertilized. Measurements of the 
amount of transpiration show that in concentrated solutions, the plant needs 
less water, for the production of one gram dry weight, than it does in very 
dilute ones. From this it is evident that, up to a certain degree, fertilizing 
signifies a saving of water^. 

The structure and size of the root system is changed gradually by con- 
centration, corresponding to the change in the root hair, already mentioned. 
Schwarz's- experiments with pines demonstrated this very well. He found 
a gradual decrease in the extent of the roots of conifers with an increase 
of the nutrient content of the soil, as had already been determined for 
other plants. Here the relation between the aerial and underground axes 
was changed. While, in unfertilized sand, the weight of the root system of 
the pine seedlings was greater than that of the aerial parts, with an abun- 
dant supply of nutritive salts the weight of the root system amounted to 
only one-fifth that of the aerial axis. 

Even in cabbage plants, which have been gradually accustomed by cul- 
tivation to the highest admissible concentrations, an over-nutrition finally 
takes place and with it a retrogression in production. Thus kohlrabi plants 
were found to be especially susceptible to large additions of phosphorus, 
while they require high nitrogen and potassium fertilization, together with a 
corresponding addition of calcium^. 

Changes in Meadows. 

The method of improving sour and sandy meadows by fertilization, 
depends essentially on an increase of the nutrient concentration. The acid- 
loving grasses, or those of sterile soil, which withstand only w^eakly con- 
centrated solutions, then disappear and our good fodder grasses, demand- 
ing higher nutrient content and producing more nutritive substance are 
established. Very instructive experiments on permanent meadows are 
found in Lawes and Gilbert*. We will cite from them only one example, 
in order to show that those different grass species gradually prevail in those 
nutrient solutions, of which they can endure a higher concentration. With 
the stated fertilizers, the percentages of the various grass species in 100 
hay plants were found as given in the following table. 

From this table of grasses, we see how the rapidly spreading Festuca 
duriuscula disappears on sterile sandy soil, if the concentration of the ni- 
trate solutions and the mineral substances increase simultaneously. Agrostis 
vulgaris and Anthoxanthum odoratmn behave similarly, while, conversely, 



1 Sorauer, P., tJber Mifsernten bei Hafer. Oesterr. Landwirtsch Wochenblatt. 
Nos. 2, 3, 1888. 

2 Schwarz, F., tJber den Einfluss des Wasser- und Nahrstoffgehaltes des Sand- 
bodens auf die Wurzelentwicklung von Pinus silvestris im ersten Jahr. Zeitschr. f. 
Porst-u Jagdwesen. January. 1892. 

3 Otto, R., Vegetationsversuche mit Kohlrabi etc. Gartenflora, 1902, p. 393. 

4 From "Journal of the Royal Agric. Soc. of England" and "Proceedings of the 
Royal Hort. Soc. 1870," cit. in Biedermann's Centralbl. 1876, II, p. 405. 



363 

the heavy feeding plants of our sewage disposal fields, Dactylis glomerata 
and Poa frk'ialis, during the five years over which the experiments extended 
(the results are given in the table), became more and more abundantly 
established on the parcels of land strongly fertilized with nitrogen, and 
crowded out the others. The grass of village streets, Brouius mollis, ap- 
peared in high percentages only when stable manure had been used, while 
Loiiiim pcrenne and Holcns lanatus were present everywhere, to be sure, 
yet spread but little where stable manure was abundantly used. 



Species of Grasses ^ -^ 



Festuca dnriuscula i3-04 

Agrostis vulgaris 8.62 

Lolium perenne 8.62 

Holcns lanatus 4.97 

Dactylis glomerata 1.76 

Poa trivialis 1.50 

Bromiis mollis 0.08 

Anthoxanthum odoratum. 3.29 

Among other interesting observations of these authors, is the one that 
the parcels of meadow land, which had remained unfertilized, exhibited 
great diversity in the families and species growing on them. The grass was 
short, stemless. and, at the time for cutting, comparatively very green. With 
mineral fertilizers, the Leguminoseae gained the upper hand, while, in the 
Gramineae, which, however, showed no especial prevailing genus, the tend- 
ency to the development of blossoms was more decided than on unfertilized 
land. Conversely, ammoniuM salts, given alone without other fertilizers, 
almost excluded the Leguminoseae, and the Gramineae, therefore, predomi- 
nated. Festuca and Agrostis reached their highest percentage, and Rumex, 
Carum and Achillea throve luxuriantly. 

If Chile saltpetre alone were used, the effect in general was the same as 
with ammoniutn salts ; nevertheless, among the grasses, Alopecurus pratensis 
was especially prevalent ; and a predominating tendency to leaf production 
also became noticeable in contrast to the development of the flower stems. 
Besides the somewhat better developing Leguminoseae, there was a lux- 
uriant development of the little useful Plantago, Centurea, Ranunculus and 
Taraxacum. 

The highest yield and the best development of the grasses was found 
with stable manure to which some fertilizer containing nitrogen had been 



>) CO 


d 


^ 


£ 


Stable-] 


Manure 


tion onl 
ith 

um Salt 


Si 

.2 to 
tsi 


neral ai 

onium 

ilizers 


'al and 

mmoniu 

lizers 


0) 


s 

3 

C u 
<i> 

£-S 


srtiliza 
mmon 


>.t< 


ith Mi 
Amm 
Fert 


Minei 

uble A 

Fert 




< 


£3 

■£fe 


fc < 





^ 



Q 




'^ 


21.42 


12.00 


2.98 


0.79 


0.22 


0.19 


21.29 


2.76 


11-55 


9-15 


1.38 


0.78 


3-39 


3-03 


11.89 


8.60 


2.59 


2-73 


9.68 


4.86 


11.06 


8.82 


2.17 


2.01 


2.27 


2.79 


5-04 


23-58 


4-85 


16.86 


1. 6 1 


577 


12.00 


15-47 


27-43 


29-34 


0.15 


0.63 


2.21 


0-93 


9.64 


12.53 


2.41 


0.80 


0.49 


O.IO 


0.19 


0.06 



1 By mineral fertilizers, the authors mean a mixture of super-phosphate with 
potassium, sodium and magnesium sulfates. 



364 

added. The Leguminoseae and other plants disappeared, having been over- 
grown by the grasses w^hich then ripen more easily than if they have only 
a nitrogen supply. Stable manure alone also yielded a considerable har- 
vest of Bromus mollis and Poa trivialis especially, with fewer Legumi- 
noseae, but it left much to be desired in the fineness and uniformtiy of 
the hay. 

If mossy meadows are brought under cultivation, the moss cannot en- 
dure a concentrated nutrient solution, or, at least, a high concentration of 
various nutrient salts which require still closer examination. This explains 
the disappearance of moss from meadows after they have been fertilized 
with potassium. The same behavior is found for the horsetail (Equisetum) 
which is said to disappear absolutely after the use of calcium chlorid, and 
seems, on this account, to be especially sensitive to high calcium concen- 
tration. 

In contrast to the extreme impoverishment of the meadows, manifested 
by a mossy vegetation, stands the over-powerful development of grass on 
the so-called rankly grozving places. There is an abundant nitrogen fertili- 
zation from the excretions of animals and its results are shown by a more 
luxuriant blade development. According to Weiske^, the plants had nearly 
twice as much protein but possibly ^ less of substances free from nitrogen, 
than the neighboring plants which had not been over-fertilized. Accord- 
ingly, the ash of the former contained more alkalis, magnesium and sulfuric 
acid. The plants on such rankly growing places, despite their greater 
volume, remained in an immature condition. With a greater spread of such 
over-fertilized places, these plants would become more injurious than bene- 
ficial. In this they resemble the condition on the sewage disposal beds. 

Sewage Disposal Beds. 

The increased use of sewage disposal beds near large cities requires 
special discussion of the injuries unavoidable in this practice. Ehrenberg- 
has recently published his experiences in regard to the Berlin sewage beds. 

Aside from the notably increased development of Plasmodiophora 
Brassicae, due to the rapidly repeated cultivation of species of cabbages, 
he reported also injuries due to animal parasites. Most of all occurred 
the extraordinary increase of Silpha atrafa, whereby great areas of beets 
were completely destroyed. The parasites found over-abundant nourish- 
ment in the decomposing organic substances of the liquid sewage and, in 
the dams and canals, lurking places where they were protected from cold 
and enemies. The great supply of nutrients also attracted the crows from 
long distances to the sewage beds on which seeds, as, for example, maize 
and wheat, were uprooted in whole rows. Rats were another pest. 

In addition to the damage done by animal and plant forms, the wind 
caused more damage here than on other fields. On the Berlin sewage beds 

1 Annalen d. Landwirtsch. 1871. Wochenblatt, p. 310. 

2 Ehrenberg, Paul, Einig-e Beobachtungen iiber Pflanzeiibeschadigungen durch 
Spiiljauchenberieselung. Zeitschr. f. Pflanzenkrankh. 1906. 



365 

a large number of fruit trees in full leaf were blown down, in spite of 
strong stakes, because the earth, which was wet through, did not support 
the roots sufficiently. This was especially noticeable if a part of the field, 
with the surrounding avenues of fruit trees, was flooded with liquid sewage. 

Sugar and fodder beets, carrots and similar roots irrigated during 
the growing season, could not withstand liquid sewage about their crowns 
for any length of time. In a few hours the leaves began to wilt and towards 
evening the petioles became limp. Grains, grass, legumes and other plants 
without fleshy roots did not react in this way. Probably the wilting is 
physiological since the scanty root fibers present on each fleshy root cannot 
draw enough water from the highly concentrated soil solution to make 
good the loss from evaporation. If the concentration of the soil solution 
was decreased by the absorption of the soil, the wilting disappeared. 

To avoid this, dams one meter wide were built, or the roots were hilled 
up as they grew and irrigated in the furrows thus produced. 

Attention has been called in another place to the change in the growth 
of grasses. On the Berlin sewage beds, Lolium italicum abounds and often 
is entirely killed if irrigated in winter. 

The softness of the grass, indicated by its easy decay, is also caused 
chiefly by an excess of nitrogen. On an average, in the years 1900 to 1902, 
a hectare of the Berlin sewage land received 800 to 1200 kg. Nitrogen^ 
In spite of the very sparse seeding and the widely separated planting the 
over- fed grain plants are usually inclined to lodge. I had an opportunity 
to study the process taking place in this lodging of oats on the Berlin sew- 
age beds-. In this, a peculiar softening of the leaf tissue, due to bacteria, 
was noticeable. Regarding the behavior of young seedlings with over- 
fertilization, I observed in barley, that, in comparison with the normally 
nourished plants, over- fertilized ones became a darker green, but were back- 
ward in growth. Then the tips of the leaves bore greyish yellow spots and 
finally turned entirely grey ; at this time a number of seedlings lodged. Soon 
after lodging, the part of the stalk above the bend began to dry. But while 
plants normally drying finally assume a straw color, only the lower leaves 
in this case became straw-colored and the upper ones dried to a hay green 
color. Of importance here is also the diseasing of the vascular bundles 
and the great predisposition of the plants to attacks of fungi•^ 

Besides the well-known delay in the ripening of grain on sewage 
fields. Ehrenberg also mentions the change in the proportion between the 
yield in straw and grain. In irrigated oats the proportion of grain to straw- 
was as I :3.33, in non-irrigated, as i :2.88. 

Such a "luxurious growth of strazv" gradually becomes typical, for 
seven newly grown varieties of barley gave an average proportion of grain 



1 Backhaus, Landwirtschaftl. Versuche auf den Rieselg^utern der Stadt Berlin 
\m Jahre 1914. 

- Sorauer, P., Beitrag zur analomischen Analyse rauchbeschadig'ter Pflanzen. 
Landw. Jahrbiicher von Thiel., 1904, p. 593. 

3 Loc. cit. p. 646. 



366 

to straw of i :i.75, while varieties grown for a long time on sewage beds, 
showed 1 :2.88. Wheat and rye behaved similarly. The amount to which 
ripening can be retarded in extreme cases, was found for red mountain 
wheat, which, sown on April 19th, ripened on irrigated fields on the 13th 
of September, but on non-irrigated, on August 24th. There was then a 
difference of 20 days. 

Mention is made in another place of the disadvantageous effect of 
chlorin compounds on the starch content of potatoes, and on other plants. 

The "coating ivith ooze and mud" is the most important injury in sew- 
age disposal beds. Liquid scivage contains, besides great quantities of 
sodium chlorid and other salts, many organic substances especially pieces of 
paper, coffee grounds and the like. Six investigations of Berlin sewage in 
1902, gave on an average : 

Organic Substances 0.030 per cent. 

Potassium 0.006 per cent. 

Sodium 0.022 per cent. 

Sulfuric acid 0.006 per cent. 

Chlorin 0.020 per cent. 

The pieces of paper and the organic substances dry up on the beds 
into tough, thin, flat cakes, decomposing only with difficulty because of 
their fatty content. Soaked with salts and organic substances, these form 
the ooze, which acts detrimentally to the soil. The high content in salts will 
easily cause a leaching of the calcium through an exchange of bases. 

Analyses^ prove that, on sewage beds covered with ooze, calcium is 
actually carried off. The calcium content amounted in 

upper surface sub-soil 

Normal soil 0-i53 per cent. 0.031 per cent. 

The same soil, but covered with ooze. 0.122 per cent. 0.048 per cent. 

An application of calcium is, therefore, desirable in soils covered with ooze, 
since its action improves the soil physically. 

The disposal of the above mentioned papery flat cakes, which may 
choke young plants, especially grasses, will have to be undertaken first of 
all by harrowing, tearing and removing the rags. Nevertheless, in planting 
the fields, great quantities get on to the soil and liave an injurious effect. 
The enrichment in organic substances, due to the ooze, may be recognized 
from the loss when heated : 

Normal soil contained (in a friable condition) ... 1.994 per cent. 
The same soil, covered wath ooze 2.418 per cent. 

Vegetative experiments in pots shouted that an admixture of ooze always 
arrested growth, and an addition of quick lime did not overcome this re- 
tardation. The arrestment in development did not show itself in the ap- 
pearance of positive symptoms of disease, but only in the delayed sprouting 

1 Backhaus, loc. cit. p. 69 and p. 114. 



36/ 





of the seed and general depression in growth. The explanation of the phe- 
nomenon should be sought in the physical domain. The ooze which is very 
impervious to water and air, 
because of its closely cemented 
particles and its fatty content 
arrests the spread of the roots 
and greatly prevents the rise and 
fall of the water. 

The Scurvy Disease. 

Among the many forms of 
disease, of which the causes 
are not satisfactorily explained, 
scurvy should be included under 
the diseases due to material ex- 
cess. The reason for this is the 
frequent observation that after 
the addition of substances tend- 
ing to increase the alkalinity of 
a soil, scurvy usually appears in 
increased amounts. 

Scurvy or "scab" consists 
of flatly spread, cork colored 
bark-like spots formed on the 
fleshy under- 
ground root, 
or storage tu- 
ber. As long 
as such a bark- 
like cleft re- 
mains super- 
ficial the dis- 
ease is called 
"surface scur- 
vy." If, on the 
other hand, the 
injured places 
deepen rapid- 
ly becoming 
grooves or 
holes, the dis- 
ease is called 
"deep scurvy." 
In certain 

cases warty outgrowths appear on the wounded surface, and this condition 
has been distinguished as "knotted scurvy." 




Fi£ 



52. 



Carrot diseased with deep scurvy, seen from the 
most diseased side of the root. 



Fig. .-1. /, /' and /-, vascular bundle rings arranged in terraces: g. holes in the 
tissue with tinder-like edges; k, tuberous parenchyma outgrowths on the carrot 
head, which may be indicated as the overgrowth tissue of the scurvy wound: s. 
initial stages of the scurvv which extend downward along the root groove (/H: 
;-, outer edge of the scurvy hollow; c. its deepest part: Fig. B. Cross-section of 
tlie carrot near the center of the deep scurvy (c) .■ Vascular bundle rings destroyed 
by the scviryy /, /' and t- which extend outward like terraces from the deepest 
part of the wound; 1 shows the poor formation of the outer vascular rings. 



368 

Besides sugar and fodder beets, potatoes suffer most frequently : also 
roots of the Umbelliferae, such as celery, carrots, parsley, etc. ; more rarely 
the fleshy roots of cabbage plants. This condition is characterized by the 
destruction of the cork layers. For some time they are replaced again and 
again by the underlying tissues. Fig. 52 illustrates a sugar beet suffering from 
"zonal deep scurvy" or "girdle scurvy," the worst form of this disease. 
The beet is 7 to 8 cm. thick at its head, but is circular only at the top ; while 
on both sides where the roots grow, there is a considerable flattening which 
disappears again toward the lower end. The flattened sides are depressed 
like troughs and the centre of the trough is possibly 6 cm. away from the 
cut surface at the head of the beet. • The inner surface of the trough is 
wavy because, around the very deep centre, the dififerent layers of the beet 
flesh rise like terraces above one another towards the outer edge in more or 
less clearly defined zones. 

The consistency of the tissue at the edges of the trough is tindery, 
scurvy-like, i. e. fissured and the fissures traversed by tube-like passages, 
which initiate a fibrous decomposition of the substance. The passage-like 
fissures are lined with brown, corked, jagged pieces of tissue, whose sur- 
faces show a peculiarly grainy decomposition. In spite of the deep decom- 
position at the place attacked, we find that the beet retains the ability to 
react, for the edges of the various rings of vascular bundles, because of a 
new cell formation, curve out like ramparts after the injury. 

That the growth of the beet at the scurvy places may previously have 
been somewhat arrested is evident from the fact that, on the injured side of 
the beet as well as on the opposite side, the different tissue rings are smaller 
than on the other sides. If cross-sections of the diseased plants are treated 
with sulfuric acid, it is found that beneath the brown, dry, gradually de- 
composing tissue layers, which have turned to cork, the intercellular sub- 
stance of the apparently healthy root flesh assumes a yellowish, wine-red to 
bright carmine tone. Often some duct groups also seem to be provided with 
solid balls, or stoppers, which assume the same color when treated with 
sulfuric acid. Later the intercellular substance is found to be broken up 
and finally begins to decompose into a grainy slime. To the naked eye the 
whole process seems a form of dry decomposition. 

As already mentioned, this form of scurvy which extends so deep into 
the flesh of the beet, is less frequent. We usually find much flatter, bark- 
like fissures, occurring in circular areas, and often showing that they have 
appeared in a rather early developmental stage of the beet, but later have 
stopped spreading. It is worth noting that, in the zonal deep scurvy, the 
head of the beet does not seem to be attacked, but the disease becomes 
visible first at a certain distance below this, in the soil. In too deeply 
planted beets the first traces of scurvy are often found at the base of the 
petioles. Very similar phenomena are noticed also in potatoes, carrots, etc. 
In potatoes, it has been observed that the scurvy formation extends out 
from the lenticels. If we examine such a lenticel, we perceive without diffi- 



PART V. 



MANUAL 



OF 



Plant diseases 



BY 



PROF. DR. PAUL SORAUER 



Third Edition— Prof. Dr. Sorauer 

In Collaboration with 

Prof. Dr. G. Lindau And Dr. L. Reh 

Private Docent at the University Assistant in the Museum of Natural History 

of Berlin in Hamburg 



TRANSLATED BY FRANCES DORRANGE 



Volume I 
NON-PARASITIC DISEASES 

BY 

PROF. DR. PAUL SORAUER 

BERLIN 



WITH 208 ILLUSTRATIONS IN THE TEXT 



Copyrighted, 1916 

By 

FRANCES DORRANCE 



t^ 



JAN -3 1917 
©CI,A448786 

THE RECORD PRESS 
Wilkes-Bai-re, Pa. 



l/Wj V 



SB73) 
.56 



3^9 

culty how fit a point it is for parasitic attack. Here, under the skin, 
formed of plate-hke cork cells (k) (in the subjoined Fig. 53), we find the 
first stages of lenticel formation beneath the stomata in the form of irregu- 
lar cells, poor in contents (a). Since this cell formation extends further 
and further backwards and the cells first formed take up water, swell and 
rupture the corky cortex, a lenticel is produced which now gives rise to 
scurvy. From it the loosened cork cells (/) push out in the form of a 
whitist, moist meal. These cells decay, and the process of decay is con- 
tinued further inward so that the close pressed, still connected rows of 
immature cork cells (v) must be sought deeper and deeper in the interior 
of the tissue. Here the starch (st) disappears from the tissue surrounding 
the cork cells. Continued moisture will develop very similar conditions in 




Fig-. 53. Lentical formation on the potato skin. 

other underground parts of plants. In this process the cork mantel, which 
has previously acted as a protection, is seriously loosened and broken apart. 
The scurvy disease has recently been considered to be parasitic and 
usually is described as due to bacteria. Therefore, it is also treated in the 
second volume of this manuaP. But there it is emphasized, that the cause 
is ascribed to very different organisms, by some, to bacteria, and by some 
to fungi. On the one hand, it is stated that these organisms should be con- 
sidered as wound parasites, which cannot attack the uninjured cork layer 
(Kriiger), while, on the other hand, inoculation experiments on immature 
organs have been carried out successfully under special circumstances. 
(BoUey). It must also be added here that a great many practical experi- 
ments have determined beyond question that, as already mentioned, certain 
substances contained in the soils favor scurvy. This explains the possible 

1 See Beet scurvy, p. 46 and Potato scab, p. 75. 



370 

connection of the scurvy disease with parasitic organisms, which, never- 
theless, are not specific scurvy organisms. It is much more probable that, 
in beet soils, saprophytic species, which are generally present, are able, be- 
cause of definite changes in the composition of the soil, to attack weakened, 
old beets, or tender young ones. The fact that the healthy vascular bundle 
rings are more slender where scurvy began, i. e., their growth in breadth has 
been retarded, proves that the beet has undergone arrestment during the 
time of the scurvy disease. 

Supported by Bolley's inoculation experiments^ which prove that beet 
scurvy and potato scab are due to similar causes, we will take up the main 
question, viz., what conditions have been determined practically as favoring 
or causing scurvy. It is Avell known among agriculturalists that marling the 
field results most frequently in an attack of potato scab. The yellow marl, 
which contains magnetic oxid (Fe., O4) is said to be the most dangerous. 
Frank has conducted cidtural experiments- to determine the problem. 
Scurvy is produced on unsterilized soil, but not on sterilized, even 
when loamy marl is added to it. As shown by experience, meadow 
ore. street sweepings, sewer muck, fresh animal manure, liquid manure and 
Chilean saltpetre all favor scurvy, which fact enforces the decision, that an 
alkaline reaction afifords the most favorable conditions for the development 
of scurvy organisms. Bolley^ also arrives at this conclusion. His experi- 
ments show that the scurvy bacteria which he used develop most rapidly on 
neutral or basic nutrient soils. Frank's comparative experiments prove 
that moisture acts favorably, and Bolley emphasizes the observation thnt 
light, sandy soils, as a rule, yield smooth tubers. Frank's results seem to 
contradict the observation that a good deal of scurvy can be found in some 
places in hot, dry years. 

These apparent contradictions are explained by Thaxter's investi- 
gations*. He distinguishes between organisms causing the deep scurvy and 
those causing superficial forms and emphasizes his conclusion that a '^eutral 
reaction seemed most favorable for the organism which he cultivated. 
Slight alkalinity, however, like slight acidity, seemed to have a retarding 
efi^ect. In his experiments young tubers were attacked at any place, older 
ones on wounded surfaces and especially on lenticels, while nearly ripe 
tubers were entirely free. 

All scurvy organisms, therefore, do not seem to require the same con- 
ditions. In common, however, they prefer lenticels and young organs with 
a delicate cork covering. In beets, the places where the rootlets arise are 
especially suitable as points of attack for the micro-organisms. These 
places become very much broken in wet soils, and this fact explains the 
assertion that moisture favors the development of scurvy diseases. Wet, 



1 Bolley, H. Ij., A. disease of beets, identical with deep scab of potatoes. Gov. 
Agric. Exp." Stat. f. North Dakota. Bull. 4, 1891. 

2 Kampfbuch gegen die Schadlinge unserer Feldfriichte. 1897, p. 177. 

3 Zeitschr. f. Pflanzenkrankh. 1901. p. 43. 

4 Thaxter, Roland, Tbe Potato Scab. Fourteenth Annual Report of the Con- 
necticut Agric. Exp. Stat. 1890. 



'371 

heav}^ soils are aerated with difficultA' and if substances are present in the 
soil, which require large amounts of oxygen, they take it from the living 
plant when a sufficient amount is not found in the soil. Refuse, sewage, 
animal manure, ferrous oxid compounds, etc., must be considered as sub- 
stances which require a great deal of oxygen. We find examples where a 
piece of land fertilized with stable manure yielded scabby potatoes, while 
unfertilized land surrounding it yielded a crop free from scurvy^. 

However, in the decomposition of sewage and other animal refuse, 
injurious sulfur compounds are produced in the soil, which will naturally 
act poisonously on the root system and yet favor certain groups of bacteria. 
As soon as such processes set in, the scurvy bacteria, which prefer neutral 
or alkaline soil, will thrive. 

Such conditions may also be produced in clay soils in times of intensive 
beat and drought ; or they can be brought about by the addition of marl 
containing iron. In this way might be explained the appearance and often 
the annual repetition of the scurvy, which may appear after marling but 
does not always set in. All the above named factors favoring scurvy 
can actually develop it in certain cases and not in others. The good 
effect of lime, already observed in many cultural experiments-, may be 
explained by its characteristic flocculating action in heavy soil, with a conse- 
quent improvement in physical texture. The soil becomes warmer, more 
porous, more easily aerated, while the animal manure is more protected 
from unfavorable decomposition. The easily aerated sandy soils, which do 
not long" contain highly concentrated soil solutions, are usually free from 
scurvy. Therefore, the various substances, said to favor scurvy, are not 
injurious in themselves but only in certain combinations, which direct soil 
decomposition into unhealthy channels. 

We have been led to the point of view here expressed by our own 
experiments^, which were intended to answer the question, as to whether 
scurvv can be retained constantly in the soil and can spread there. The 
result was negative. In the two successive experimental years not only the 
tubers obtained from healthy seed, but, with a very few exceptions, even 
those originating from scabby potatoes were healthy. Thus it is clear that 
the condition of the seed does not necessarily determine that the scab dis- 
ease will be present in open land, and so the much recommended steriliza- 
tion is unnecessary. The recommendations for combatting the disease must 
be based on a change in the constitution of the soil and especially on the 
avoidance of substances which favor scurvy. In regard to the oft-asserted 
injuriousness of lime, my experiments have proved that tubers, some of 
which were brought directly in contact with the lime, remained perfectly 
smooth skinned and healthA^ Recentlv, substances have been introduced 



1 Arb. d. D. Landw.-Ges. Jahresbericht d. Sonderausschusses f. Pflanzen- 
schutz 1904. 

2 Kriig-er, Fr., Untersuchungen iiber den Giirtelschorf der Zuckerriiben. Zeit- 
schrift d. Ver. d. Deutsch. Zuckerindustrie. Nov. 1904. 

3 Zeitschr. f. Pflanzenkrankh. 1S99, p. 182. 



372 

into trade which are said to increase the reaction of the soil (for example, 
sulfarin). 

In connection with scurvy diseases of edible roots, we would like to 
call attention also to similar phenomena on smooth barked young trees, 
which have not as yet been studied. Lindens, elms, oaks, etc., on certain 
kinds of soil (i. e. moor-soil) had round, rough splits in the bark, which 
increased greatly in extent adjacent to the adventitious buds or shoots. 
This bark scurvy is frequent near large cities, where the base of the tree is 
exposed to debris of all kinds. 

Another phenomenon found in barley and wheat, which should be in- 
cluded in this group, is "spotted necrosis," i. e., the appearance of deep, 
dark reddish brown, dying spots at the tip and along the edge of the grain 
leaves. Up to the present, I have found the disease most extensively in 
heavy, clayey, or moor soil, which had had abundant potassium fertilization 
and also in regions with a deposit of ashes. 

Progressive Metamorphosis. 

W'hile, in the cases already discussed in this chapter, we have empha- 
sized as the common characteristic of all the phenomena, the influence of 
unsuitable concentrations of the soil solution, because of which the plant 
suffers, we will now consider the cases in which the plastic building sub- 
stances have been increased out of proportion to their utilization. Here, too, 
an excessive supply of nutrients in the soil does not give rise necessarily to 
this condition, but, for various reasons, a disturbance in the equilibrium in 
the formative direction of the individual may occur, that is to say, a change 
in the utilization of the plastic food materials. 

Examples of this are those phenomena grouped under progressive 
metamorphosis, such as the transformation of leaf organs into a morpho- 
logically higher developmental form. Teratology classifies such transfor- 
mations under the heads "petalody'' and "pistillody," i. e., cases in which 
the calyx bracts become petal-like, or parts of the corolla assume the char- 
acter of the stamens, or the organs actually belonging to the androe- 
cium circle are changed into carpels. Numerous examples of peta- 
lody are furnished by the cultivated forms of our Primulae and Ranunculi. 
We find the best instances of pistillody in the poppy (Papaver sornni- 
ferum). Tn this plant, as in the dififerent varieties of cabbage, long con- 
tinued cultivation has so disturbed the morphological rules, that the organs 
tend to transformation. A most interesting case may be found in the poppy 
heads which, at the base, bear a circle of many small, woody primordia of 
smaller heads (stamens which have been changed into carpels). Tn double 
tuberous Begonias, tulips and other Tlliaceae, specimens are found in which 
the stamens have been transformed into carpels with seed primordia. Re- 
lated to this are the phenomena of the "cone malady" in conifers, especially 
in pines, as illustrated in Fig. 54. 



373 



In the majority of 
cases, the cones at the base 
of an annual shoot he close 
together and remain small- 
er than normal ones, but 
yield seeds capable of ger- 
mination. The production 
of such cones, instead of 
staminate flowers, points 
to a local excess of con- 
centrated, plastic food ma- 
terial. Borggreve^ has made 
a corroborative observa- 
tion. He found, the year 
after transplanting several 
spruces, possibly 15 years 
old, in the Botanical Gar- 
dens at Bonn, that the 
terminal shoot had been 
transformed into a pistil- 
late inflorescence. 

If an excess of plastic 
building substances partici- 
pates in this, so that the 
various leaf members of a 
blossom retain their form, 
but the axis is lengthened, 
we speak of the disunion 
of parts of the blossom 
normally united as aposta- 
sis. The calyx, for ex- 
ample, then appears sepa- 
rated from the corolla by 
a long internode, the cor- 
olla in turn from the 
stamens, etc. 

The most perfect form 
of over-nutrition of the 
blossoms is found in the 
so-called "Rose-Kings," i. 
e., in the roses in which a 
new blossom springs from 
the center of an older one. 




1 Forstliche Blatter 18S0. 
Vol. 17, p. 245. 



Fiff. 54. 



Cone disease in the Scotch pine. 
(After Nobbe.) 



374 

or new blossoms appear laterally. A\'e term such cases proliferous shoot 
development {proliferation). Unusual buds arise inside of one blossom 
or of one inflorescence. 




Fig. 55. Sprouting- pears. 

Such buds sometimes develop into blossoms, sometimes into leafy 
shoots. If such an adventitious bud stands in the centre of a blossom, so 
that the axis of the flower appears to end in it and can be continued only 
by the development of this bud, we call such a proliferation diaphysis. If, 
on the other hand, the adventitious bud appears in the axil of any member 
of the inflorescence, or the bracts, the formative variation bears the name 



375 



of axillary proliferation, the appearance of buds within the 
flower (ecblastesis). Sprouts in the centre of the blossoms 
are more frequent than those in the axils, a circumstance 
probably connected with the fact, that all shoots, which form 
the direct continuation of the erect axis, obtain water and 
nutrition more easily than do lateral branches. In favor of 
this is also the very rare occurrence of proliferations in 
flowers which stand isolated in the axils of leaves. 

The doubling of blossoms in the Compositae consists, as 
is well-known, mostly in the change of the normally tubular 
labiate flowers into brightly colored ligulate flowers (ray 
florets). Proliferation in the Compositae has often been ob- 
served, when, instead of the separate florets, a whole head is 
produced at the base of the inflorescence. Thus Magnus' 
reports specimens of Bellis perennis which had numerous, 
stemmed secondary heads around the edge of its heads. The 
same phenomenon has been observed at times on Crepis 
biennis, L. as well as on Cirsium arvense Scop. Everywhere 
the individual florets were so developed that they had a more 
or less long stemmed axis, often provided with dry, mem- 
braneous leaflets and crowned by a small but perfect flower 
head. In fact, on the edge of each secondary head, tertiarv' 
heads and even heads of later orders may develop. 

Similarly sprouts from phanerogamic fruits are not rare. 
The best known examples are found in our pomaceous fruits 
and, of these, more often in pears than in apples. We give 
in Fig. 55 an illustration of sprouting pears, in which one or 
more secondary fruits develop on the primary fruit. This 
phenomenon may be explained by considering the fruits of 
our pomaceous fruit as twigs, of which the bark has developed 
extraordinarily. Usually, the tip of the twig ends in the 
carpels. These develop into a core and bear the seeds inside 
this core. The bark of the twig swells, depressing more and 
more the terminal blossom above the seed primordia and be- 
comes the flesh of the fruit by material changes and cell- 
elongation. As in tlie proliferation of the rose, a pear blossom 
may also develop a secondary blossom in its centre, in which 
the small axillary crown between the embryonic carpels 
elongates ; the carpels are pressed apart, or do not develop at 
all. This secondary blossom matures into a twig, sprouting 
from the firts pear. This develops a blossom at its tip or, 
without it, swells out like a top, thus producing a second pear 
on the first one. If these twigs do not develop sexual organs, 



1 Sitzungsber d. 
Sitz. V. 28. Nov. 



Bot. Ver. d. Prov. Brandenburg XXI, 1879. 



Fig. 56. 
Larch cone 

with growth 
of the axis 
continued. 

(After Nobbe.) 



376 

the monstrous pears have no core. If the prohferous axis of the fruit 
divides, lateral, smaller pears sprout around the central one. 

In apples, the ability to sprout often extends only to some branches of 
the vascular bundles in the fruit. Then a knot swells out at the side and 
can increase to a small secondary fruit. If the lateral sprout develops and 
produces an actual bud, we find two cores lying diagonally above one 
another. This case bears great resemblance to double fruits which arise 
from the union of two separated, laterally placed embryonic flowers. A 
simple case is the development of a dormant leaf bud on the unthickencd 
part of the fruit, i. e., the stem. 

In conifers, prohferation is found in the continued growth of the cone 
axis into a needled branch; this may be found most often in larches (see 
Fig. 56). 

Among the phenomena in which an excess of plastic food material is 
manifest, belongs also the occurrence of leaves at places on the axis which 
normally should be leafless, Chorisis, and the increase of the leaf organs 
in a node {Doubling, Dedoublement) as also the multiplication of parts of 
a compound leaf (Pleophylly). The most common example of the last 
case is the four-leafed clover. Tammes\ in a recent study of this case, 
mentions that De Vries, by continued selection, has created a race, the in- 
dividuals of which possess four to seven leaves. This is also a very good 
example of the way in which phenomena of over-nutrition, once produced 
accidentally, may become hereditary. We referred to this point also in 
treating of fasciation. In the clover, individual veins and even the mid- 
rib seem more vigorous and are divided, at times extending even into the 
petiole. Then each part of the divided petiole bears leaflets at its tip. 
Pleophylly also deceases on the branches of the second, third and fourth 
order in which the supply of nutrients decreases in contrast to the first 
produced, vigorous axes. We find less striking examples in all plants. 
Leaves which display especially strongly developed leaf surfaces and then 
a forking of the different veins are found everywhere on the branches 
most favorably located for the supply of nutrition. 

Such luxuriantly developed forms are found most often in the so-called 
sprouting of the stock, i. e. sprouts growing from dormant and adventitious 
buds on the stumps of felled trees (for example, Populus and Morus). 
The size proportions usually far exceed the average and the leaf forms 
often vary from the type, even to unrecognizable forms. In these cases the 
newly produced shoots have the whole store of reserve substance of the 
tree stump at their disposal, which causes their enormously increased 
growth. 

As related phenomena we will also name here the witches-broom which 
we may pronounce a "twig -malady." The accumulation of the plastic food 
material in various places in the branch, which gradually seeks utilization 

1 Tammes, Tine, Ein Beitrag zur Kenntnis von Trifolium pratense quinquefolium 
de Vries, Bot. Zeit. 1904, Part XI, p. 211. 



377 

in a proleptic bunched formation of branches may be produced, in the ma- 
jority of cases, by parasitic stimulation. As a rule, the abnormally formed 
axes deviate structurally from normal ones^. 

Further, there belongs here retrogression to the juvenile form- in trees 
which sprout vigorously after great injury. The so-called rosette shoots, 
as shown for a pine in Fig. 57, result from local over-nutrition, due to the 
fact that the trees have previously suffered very great loss of foliage 
(usually from the attacks of caterpillars). The mobilized building sub- 
stances, which have thus lost their province of nutrition, now stream toward 
the dormant buds, lying between the normal clusters of needles or more 
clearly recognizable in the form of weak whirls, and cause them to sprout. 
Instead of clusters of needles, simple broad, sword-like needles with serrate 
edges are then produced. In their axils, as shown in the figure, the normal 
short shoots (clusters of needles) may 
again be formed. 

If we consider these cases as a whole, 
we perceive at once a feature common to 
all. It is the excessive presence of build- 
ing material in one part of the axis. In- 
deed, by over-nutrition, organic sub- 
stances, actually newly formed by the 
leaf apparatus, are placed at the disposal 
of a part of the axis, or an accumulation 
of the structural material is produced pig. 57. Rosette shoot of a 

locally since the mobilized reserve sub- Scotch pine. 

stance does not find its normal utilization , ,, , f.u ■ , 

111 the .ixils 01 the simple sword-hke needles 

due to some injury such as attacks of are shown the short shoots with double 

J J needles. (Enlar.ered.) (After Katzeburo.) 

caterpillers, pruning, storms, etc. If this 

excessive material reaches the existing primordial organ, it becomes 
manifest in the increased development of the normal form, or, within the 
compass of progressive metamorphosis, of other organic forms. If the 
structural substances reach a vegetative point, additional organs are formed. 
Each vegetative point is always the product of the food at its command. It 
retains its distinctive morphology only as long as the nutritive process re- 
mains the usual one. If the amount of structural material is increased, the 
vegetative point forms additional primordial organs, thus changing the laws 
of the leaf arrangement, determined by heredity. New normal, vegetative 
points may develop in the form of buds. There are, therefore, no steadfast 
characteristics in an organism and cultivation constantly changes the in- 
herited structural type. 




1 Compare Zang-, Wilh., Untersuch. iiber die Entstehung- des Kiefernhexen- 
besens. Ber. d. Kg-1. Lehranstalt f. Weinbau usw. Geisenheim 1905, p. 235. Abun- 
dant material has been furnished recently in the Naturwiss. Zeitschr. f. Land- u. 
Forstwirtschaft. 

2 Diels, L,., Jugendformen und Bliitenreife im Pflanzenreich. Berlin 1906. 
Gebr. Borntrager. 



378 

Pressure of the Buds (Blastomania A. Br.), 

In the preceding section the so-called "sprouting of tke stock" has been 
considered. The phenomena are observable everywhere where large trunks 
of poplars, oaks, beeches, chestnuts, etc., have been felled. On the cut sur- 
face of the stump a callus arises from the cambial zone and numerous ad- 
ventitious buds are formed on this. The various processes of propagation 
by "leaf-cuttings" of Begonias, Gesnerias, etc., show that new buds may be 
produced on the cut surfaces of herbaceous stems and leaves. The peculi- 
arity of "viviparity" should be presupposed as equally well-known, i. e., the 
development of new vegetative buds from an uninjured leaf blade during 
the normal course of development (Asplenium, Bryophyllum, etc.). Fre- 
quently observed, but abnormal cases, are similar formations of buds in 
Cardamine pratensis, Drosera intermedia^ Arahis pumila, etc. Duchartre 
found small leafy shoots growing out of leaves of Solanum Lycopersicum. 
Braun observed such excessive formation of adventitious buds on the leaves 
and especially on the stems of the cultivated forms of Calliopsis tinctoria. 
For example, he could count about 300 on a piece of stem possibly 20 cm- 
long'. Similar cases have also been observed on other plants-, and I found 
specimens of Pelargonium zonale and P. pcltatum with disc-like, fleshy 
outgrowths at the base of the stem which were entirely covered with little 
buds. Individual, more vigorous specimens developed to such a point that 
even very small leaves could be distinguished; the majority of the buds 
died because of mutual pressure. A similar fleshy cushion was formed by 
a Dahlia variabilis tuber which had been forced in a propagating case, in 
order to develop new eyes from the base of the stem. The shoots were cut 
off immediately for use as cuttings, whereupon the growing stum.ps de- 
veloped new lateral shoots from their basal buds, which became more and 
more numerous but increasingly weaker. In this way a herbaceous goitre 
gnarl was produced. 

The Goitre Gnarl of Trees. 

With the rarely occurring bud accumulation in herbaceous plants, 
above mentioned, there is naturally connected a formation of goitre gnarls 
in trees, which, with few exceptions, are produced when the growth in 
length of normal branch buds is prevented, thus inducing the sprouting of 
new lateral buds in their stead. The shoots from such buds stand closer, 
the nearer they are to the base of the branch from which they arise, because 
the internodes are shortest there. If the tip growth of such shoot primor- 
dia is limited by injury, or some other cause, such as mutual pressure, they 
again develop lateral shoots. 

The illustration from a trunk of Acer campestre in Fig. 58 gives a 
fine example of a goitre gnarl. After the noticeably thick bark had been 



1 Braun. A., tJber abnorme Bildung- von Adventivknospen am krautartigen 
Stengel von Calliopsis tinctoria, Dec. Verh. d. Bot. Ver. d. Frov. Brandenburg, XII, 
p. 151. 

2 Magnus, P., Verh. d. Bot. Ver. d. Prov. Brandenburg, XII, p. 161. 



379 




Fig-. 58. Peeled, gnarled growth of the maple. 



38o 

removed, the wood showed the spike-like processes of the dead bud cones. 
The surface view is given at a; at b the cross-section of the spike-Hke wood 
cones with the medullar}' parencliyma indicated by the darker inner circles. 

Similar structures appear in very different tree genera and at will in 
places on the aerial axis as well as in the buds of the root stock, — ^but here 
more rarely. The places exposed by the removal of branches are especially 
preferred. Here the latent and adventitious buds, accumulated at the base 
of the branch, begin to develop into small shoots. The wood elements. 





Fig. 59. Formation of gnarls on 
the branches of Malus sinensis. 

(After Kissa.) 



Fig. 60. 
Cross-section through a gnarl cushion. 



It is seen that the central part of the individual spikes of 
the Knarl is produced by a broadening of the medullary 
ray of the branch axis. (After KisSA.) 



arising from the cambium of the trunk, take a serpentine course around the 
bud cones, because they are prevented by them from extending through the 
cambium. The plastic food material is, therefore, not conducted so readily 
towards the base of the trunk. But the economy of the tree suffers little, 
as the gnarled swelling usually occurs on one side of the axis, so that the 
opposite side lies free and remains constantly accessible for normal 
nutrition. 

Nevertheless, normal branch primordia may not always be assumed 'as 
the points of departure of gnarl formation. There are also cases in which 
the spikes of the gnarl arise from excrescences of the medullary rays. One 



38i 



such case is treated in a study by Kissa^ on gnarl formation in Malus 
sinensis, which he conducted under my direction. Fig. 59 shows a branch 
of gnarl cushions, which have sprouted chiefly from the parenchymatous 
base of a small fruit shoot. 

In cross-section, it is seen that the conical spikes represent wood 
cylinders, of which the central tissues have arisen from broadened medul- 
lary rays. This kind of medullary ray (Fig. 60) is either primary or is 
produced only in a later annual ring. The wood layer of the spike is a 
continuation of the wood ring of the mother branch. As in a normal 
lateral axis, the spike of the 
gnarl is covered by its own 
bark and has also a well de- 
veloped cambial layer. Just 
like a normal branch, the spike 
of the gnarl ramifies (Fig. 60 
hm') and lengthens by apical 
growth. But not one of these 
axes at any time bears the 
primordia of leaves or buds. 

The differentiation of the ' \ 
tissue of the spike of the gnarl 
takes place in the very first 
developmental stages inside the 
bark of the mother branch, 
which at first appears to be 
only swollen. This swelling is 
produced from the upward 

forcing of the bark by a num- 
ber of especially strongly de- 
veloped medullary rays, pro- 
vided with meristematic tips. 

By the further apical growth 

of these structures, the bark of 

the mother branch is finally 

ruptured and the spikes of the 

gnarl, covered with their own bark, now appear as independent structures. 

But growth in length soon ends since the bark cap and the underlying 

meristematic layer dry up. Instead of an apical growth, a basal, lateral 

sprouting now takes place in the difi:"erent gnarl spikes in the interior of 

the mother branch. 

In Fig. 60, the cross-section of a branch covered with gnarls, we see 

that the medullary rays forming the pith of the spikes are mostly primary, 

and, therefore, arise from the pith of the mother branch, sp indicates the 




Fi.E 



61. Longitudinal section through the 
.spikes of a gnarl. (After Kissa.) 



1 Kissa, N. W., Kropfmaserbildung bei Pirus Malus sinensis. Zeitschr. fur 
Pflanzenkrankh. 1900, p. 129. 



spike ; m, pith ; A, wood ; r^ bark ; c, cambium ; insf, medullary rays of the 
mother branch ; hm, wood layer ; rm, bark layer of the spike ; n, meristematic 
cap of the spike; hm', rm', wood and bark, of the lateral sprouts of the 
gnarl cone; h', second annual ring; h" , third annual ring. 

Fig. 6 1 is a highly magnified longitudinal section through a spike of a 
gnarl lying within the bark of the mother branch. Pli, indicates the phel- 
logen ; k, the cork layer ; Fc, the collenchymatically thickened cells ; Pr, the 
I)arenchyma of the primary bark of the mother branch, of which the inner- 
most layers begin to be filled with starch ; St, 
starcli ; .Ihp, dead layer of parenchyma cells of 
the primary branch bark ; M, meristematic tip of 
the spike; /J, cells of the wood layer of the gnarl 
cone with their pores (For) ; c, cambium ; B, 
bark of the spike. 

Therefore, the cone mantel (Abp), composed 
of the shaded ce-lls, forms the boundary between 
the spike primordia and the mother bark of the 
twig and may be clearly recognized as the axial 
cylinder, since the wood layer (A) is covered 
with its own bark tissue (B) while, between both, 
the cambial zone (c) becomes recognizable. The 
wood cylinder is composed chiefly of very porous 
parenchymatous wood (For). The bark tissue 
abounds in starch. The young spike is lengthened 
l)y the apical growth of its meristematic cap, and 
gradually compresses the adjoining cells of the 
mother bark into a yellowish layer (Abp). Above 
this dead cell layer, the mother bark is still per- 
fectly healthy and dies only if ruptured by the 
gnarl cone. 

In the above statements, we have paid special 
attention to the structure of the completed gnarl 
cone, and Vvill now turn to the processes of 
broadening the medullary rays, which initiate the 
formation of the gnarl cone. I have studied one 
such case in Ribes nigrum'^. 
Fig. 62 h shows the accumulated beady gnarls, up to one millimetre in 
height, which lie side by side, or partially over-lapping. In the cross-section, 
Fig. 63, is seen the radiation of the wood ring of the branch, in fan-like 
or feathery subdivisions, into the body of the gnarl which in this case is 
not conical, as in Malus sinensis, but resembles a spherical wart. 

Fig. 63 gives at B the longitudinal section, at A the cross-section of a 
gnarl wart. -D is the normal axis of the branch with its pith body (m) and 
wood ring (A), which now seems cleft by the excrescent medullary rays 




Fig. 62. Bead-like for- 
mation of gnarls in the 
black currant. 



1 Sorauer, P., Krebs an Ribes nigrum. Zeitschr. f. Pflanzenkrankh. 1891, p. 77. 



383 

(mst). These medullary rays form the point of departure for the fan-like 
gnarl formations (sp) which, in later development, display a central wood 
body (kh) and a distant bark layer (r). 

A cross-section through the branch at such a warty place shows (Fig. 
64) that the wart represents a conical 
outgrowth (k) of the inner bark, 
which has ruptured the outer bark 
layers, but is still covered by them, 
like lips (/). The edges of the lips 
are dead, and a m}-celium is usually 
foimd in the depressions. This grows 
out into the outer, browned and dying 
or already dead cells of the primary 
gnarl cone (p). If we trace back the 
excrescent tissue which, towards its 
base, possesses a wood layer com- 
posed of slender, reticulately thicken- 
ed vascular cells, passing over into 
the normal wood ring, it is found 
to be only a simple outgrowth of a medullary ray. 

Fig. 64 illustrates an advanced stage of the medullary ray outgrowth 
of a branch at the end of the first year (the year of its production) ; the 
left side still shov.s the normal bark structure; at ak are the suberized 

.1 




Fig-. 63. 
of a 



Cri)ss-section through a part 
twig- covered with gnarls. 




Fig. G4. Cross-section through the bark of the black currant; healthy tissue 
at the left; at the right a continued outgrowth of the medullary rays. 



remnants of the outermost bark layers shed in the course of the year of its 
production, which contain scattered crystals of calcium oxalate. These 
remnants are still connected in places with the discolored, uninjured cork 
lamellae (gk) which enclose the twig, like a firm, uniform girdle. Below 



3& 






the cork layer He the collenchymatically thickened bark layers (c o) ; these 
border on the parenchyma containing the chlorophyll (chl) which is seen 
separated into zones by tangential calcium oxalate bands (o, o\ o^). The 
normal bark of the healthy branches also not infrecjuently has tangential 
cavities along these bands of crystals, produced by the tearing of the cells 
which remain thin-walled and contain small deposits of calcium oxalate, so 
that some of the crystals appear to be lying free near the edges of the 
cavities. 

In the autumn of the first year, the phloem rays may be seen to extend 
as far as the first oxalate band (o). Adjacant to these rays, as is usually 
the case in our woody plants, the cambial zone (c) curves outward over 
the wood, and then in again, like a bow. This shows that the medullary ray 

assists in the radial extension of the axis, 
just as the pith cylinder itself causes the 
longitudinal stretching. 

On an average the normal medullary 
ray (m) retains, inside the bark, the 
number of cells last formed in the wood 
and its extension in the bark then depends 
only on the greater distension of the in- 
dividual cells. Near the excrescence, 
however, medullary rays are often found 
of which the cells have increased in 
number (in') but have kept essentially 
their radial, normal elongation. An ex- 
Fig. 65. Medullary ray in the first traordinary cell increase finally takes 
stages of tiie gnari formation. place in the ray of the excrescence and the 

cambial zone curves abruptly outward. 
This is best seen in the comparatively few cases in which the medullary 
rays begin with the formation unilaterally of excrescent tissue, as shown in 
Fig. 65. In this figure m indicates the cells of the medullary ray within the 
wood ; c the cambial zone wdiich at the right side rises towards the wood 
(A) and sinks back at the left side over the wood; nr is the normal side of 
the bark ray, which pushes against the thick-walled bark parenchyma (p) 
and, in caustic potash, is clearly differentiated from its surrounding tissue 
by its yellower color. At are indicated the very thin-walled small cell 
rows containing calcium oxalate; here, near the cambial zone, the walls of 
these cells show a peculiar granular consistency as an indication of their 
approaching decomposition. Such a granular, slimy decomposition of these 
cell bands and the movenient of the calcium deposits to the edges 
of the cavities thus produced is also found in the normal bark. On 
the excrescent side (wr) of the bark ray, of which, the cells turn a still 
darker yellow after treatment with caustic potash, than do those of 
the normal side, and not infrequently display a distinct knot-like swell- 
ing of the w^alls, the cambial zone turns abruptly outward (c') and indi- 




385 

cates that it will curve outward like a cap in the mature tissue of 
the excrescence. 

This conical elevation of the cambial zone is visible in Fig-. 64 wc. 
It forms also an apical region, which, however, does not lie at the outermost 
tip of the excrescence but always remains covered by bark tissue, which 
dies from the outside inward until it reaches the meristematic tip of the 
excrescence cone. 

The apical as well as the basal region of the meristematic zone of the 
gnarl cone begins to develop shoots in the following year. Successful 
sections, showing the full course of a medullary ray. demonstrate that the 
formation of the secondary axes takes place repeatedly in the same M^ay in 
which the primar}^ gnarl cone was produced, — viz., by the outgrowth of 
part of the medullary ray extending through the bark. 

If the structure of the internodes is traced from the spot already 
recognizable as the primordium of a gnarl towards the younger parts of 
the branch, a lack of uniformity in the structure of the medullary rays is 
seen in the very weakly developed wood ring of the axis. At the base of 
the buds of the current year in which the immature wood cylinder has only 
the spiral ducts of the pith crown and a few libriform fibres, together with 
scattered, reticulated or porous ducts, medullary rays may be found here 
and there which vary from the other rays in the somewhat greater width 
of the cells, the somewhat stronger refractive power of the cell walls, the 
distinct straight course and the further continuation in the bark. It is 
noteworthy here that the end of the phloem ray extending furthermost 
into the bark, unlike the other phloem rays, is not more slender than those 
behind it, but broader, in fact, the broadest of all the cells composing the 
ray. While, therefore, the normal medullary rays are conical, this one has 
turned its broadest base toward the periphery. This is the same tendency 
in growth, found in the older stages, which appear as distinct excrescence 
rays. Such a differentiation in the earliest stage shows how this goitre 
gnarl formation is prepared in the first juvenile phases of the axis. 

Besides the excrescences of the medullary rays, there are still other 
factors which distend the bark during the encysting of diseased tissue 
centres. We will return to these points in the section on the "tuber gnarls" 
which are best treated under the processes of wound healing. 

I had an opportunity to obser^^e in Primus Padus the formation of 
goitre gnarls, which branch like witches broom, and have found similar 
structures on gooseberries^ I also found warty gnarls, similar to those 
described in Ribes, in Cydonia vulgaris^. On gooseberry bushes near com- 
post heaps, I could later determine gnarl structures in a form similar to those 
in the black currant^ In a case in the red cherry currant, of which I heard 
only recently, long leafy shoots which had no mature buds on their leaf 



1 Jahresbericht des Sonderausschusses fiir Pflanzenschutz. Arb. d. Deutsch. 
■Landw.-Ges. 1898, p. 145. 

2 Ibid. 1899, p. 188. 

3 Ibid. 1900, p. 213. 



386 

axes, developed from a goitre-like gnarl-knot. At the places where the pith 
bridge in the branch node otherwise leads to the bud, either no meristematic 
layer was found or it remained covered by a bark cap and developed into 
a small gnarl spike. Instead of the apical bud, I found accumulations of 
spike primordia which, in the following year, became actual goitre gnarls 
from which sprouted weak, leafy branches, as in Acer and Tilia. 

So far as may be concluded from their description, the remarkable 
"cylindrical gnarls" (chichi, nipple) on Gingko Biloha may also be in- 
cluded under the goitre gnarls. According to Kenjiro Fujii^ these chichi 
or nipples are found to be cylindrical or spherical excrescences which, as a 
rule, grow down perpendicularly from older branches. Their size varies 
from the length of a finger to 2 meters, with a thickness of 30 cm. They 
resemble normal branches, on Mdiich all foliage is lacking. Having reached 
the soil, they strike root and then are able to develop leaves. Similar for- 
mations are said to occur on the roots. 

I have given a more thorough description to this form of the goitre 
gnarl formation, in which normal embryonic buds do not participate, be- 
cause it demonstrates the importance of the medullary ray tissue in a way 
which, as yet, has not received the slightest consideration. Frank- cites 
references, deserving attention, and also describes earlier observations on 
gnarl structures. In this, however, the chief concern is the explanation 
of the wavy course of the wood fibres in gnarled wood. We lay the chief 
weight on the causes, which lead to the broadening of the medullary rays. 
The form of goitre gnarl, last described, is only the extreme of a tendency 
to an excrescence of the medullary rays, which may lead to certain canker 
swellings. In them, however, processes are involved which are caused by 
wounds, while here we can ascertain internal disturbances in the equilibrium 
of the processes of growth, but no external ones. 

■ We are concerned with local increases of pressure and turgor con- 
ditions brought about by the form of nutrition. Kny's^ investigations in this 
connection, give us the desired proof. He found, in the action of mechani- 
cal pressure, that, in the meristematic cells of the medullary rays, the di- 
vision walls take a dififerent direction and produce two-rowed medullary 
rays. In this instance, the results of mechanical pressure from outside, 
must, according to our conception of the matter, be afifected also by the 
mutual pressure of the tissues upon one another, caused by increase- in 
turgor. Since, however, turgor, — a sufficient water supply being pre- 
supposed,- — depends on the constitution of the cell contents, on the abundant 
presence of compounds which attract water, each increased supply of plastic 
food material will give rise to an increase in turgor and a change of the 
existing pressure conditions in the different tissue forms. 



1 Kenjiro Fujii, On the nature and orig-in of so-called "chichi" (nipple) of 
Gingko biloba. Bot. Magazine. Vol. IX, No. 105. 

2 Frank, A. B., Die Krankheiten der Pflanzen. 2d ed., Part 1, p. 82. 

3 Knv, L,.. tJber den Einfluss von Druck und Zug usw. Pringsheims Jahrb. 
f. wiss. Bot. 1901. Vol, XXXVII, p. 55. 



387 

Such an increased supply of plastic food material is present, if some 
disturbance in the normal economy of the plant arises, due to the removal 
of certain centers of consumption. Goitre gnarl formation arises from the 
removal of branches necessitated by trimming the trunks and various other 
kinds of pruning. We find striking examples of this in lindens, poplars, 
maples, etc., planted along streets ; in an ever-increasing accumulation of 
buds at the places where branches have been removed. If such gnarl accum- 
uations occur at especially preferred places, well suited for the work of 
assimilation, some shoots from these gnarls gain the upperhand and ap- 
proximate water sprouts. 

c. Effect of an Excess of Nitrogen. 

As seen already, a disturbance in the formal development of the plant 
body by a local accumulation of the prepared building materials is. to be 
sure, of interest scientifically but has no great disadvantage agriculturally. 
Indeed, we actually find that the cultivation of such formal variations, as 
doubled flowers, is often intentionally increased. The conditions are very 
different, however, if the material processes are unequally affected by the 
raw materials. Here the question of fertilization comes primarily under 
consideration and disturbances are especially involved which are produced 
by an excess of nitrogen and an unequal increase of the supply of potassium. 

We have already mentioned the fact that the soil will be injuriously 
influenced physically by an over-abundant supply of soluble fertilizing salts. 
Even if the salts keep the soil damper, as long as sufficient atmospheric 
precipitation is present, yet they form a constant menace for the plants in 
time of drought, because a too highly concentrated soil solution may easily 
be produced, making more difficult the passage of the water into the plant 
roots^. This cannot fail to have some effect on the development of the 
plant. Gerneck's- work throws some light on this subject. He observed in 
Triticum that root hairs were formed more abundantly if Ca(NO:,)2 was 
added than if KNO^ was used. In feeding with nitrates, the blades and 
ears developed late, while, with chlorid and phosphate fertilization, they 
appeared early. With the latter method, the root cells appeared to be more 
thickened than with the former, in which the epidermal cells and the leaf 
schlerenchyma were also the least lignified. 

We will now discuss a few special cases. 

Over-Fertilized Seed. 

The erroneous theory that plants can be brought to unbounded per- 
fection by abundant fertilization has given rise to an endeavor to give seeds 
additional help by fertilizing them at the time of sowing. The seeds were 
either "candied," i. e. coated with a crust of nutrients, or they were soaked 

1 Wollny, Ij., Untersuchungen liber den Einflus.s der Salze auf die Boden- 
feuchtigkeit. Vierteljahrsschr. d. Bayer. Landwirtschaftsrates 1899. Supplement 
p. 437. 

- Gerneck, R., tJber die Bedeutung- anorganischer Salze fiir die Entwicklung- 
und den Bau der hoheren Pflanzen. Gottinger Dissertation, cit. Just, ,Bot. Jahresber. 
1902, II, p. 301. 



388 

in more or less concentrated nutrient solutions. The discovery was then 
made immediately, that such treatment assistance is often useless, and some- 
times injurious. 

Fertilization experiments with beets, made by Fremy and Deherain, 
throw some light on this point. They proved that ammonium sulfate and 
potassium salts have an injurious effect on the germinative process, and 
they also found that germination failed entirely, even with a concentration 
of 0.2 per cent. The results of soaking experiments made by Tautphous^ 
with beans, peas, maize, rape, rye and wheat proved that seeds soaked in 
distilled water germinated best of all and that the capacity for germination 
was the more reduced, the more concentrated the solutions (potassium chlo- 
rid. sodium chlorid, (commercial) sodium nitrate, potassium sulfate, potas- 
sium phosphate and calcium nitrate in a solution of 0.5 to 5 per cent.). Rape 
germinated in a 2 per cent, solution almost as well as in distilled water, 
while the other seeds were considerably impaired, even in a 0.5 per cent, 
solution. The development of the seedlings was considerably more lux- 
uriant in a 3 per cent, sodium chlorid solution than in distilled water. 

Fleischer- reports on an experiment made in East Prussia, in fertiliz- 
ing potato seed with kainit and superphosphates ; a considerable number 
did not sprout and at the time of harvesting were found unchanged in the 
soil. The analysis of these tubers gave a content of pure ash nearly twice 
as great as the average values given in Wolflf's ash analyses. In a thousand 
parts of dry weight the ungerminated tubers, compared with normal ones, 
contained potassium in the proportion of 37 to 22. While the calcium con- 
tent was almost the same in the diseased and normal tubers, the magnesium 
was apparently twice as great in the former ; the phosphoric acid almost 
double, and the chlorin content thirteen times as great as in the normal 
tubers. The sulfuric acid also increased to four times the amount in one 
thousand parts of dry weight, so that it is evident that exactly the elements 
of the kainit (potassium, sodium, magnesia, sulfuric acid and chlorin) had 
undergone an unusual increase in the ash of the unsprouted tubers. In the 
present case, the fertilizer was applied in the spring directly before the 
potatoes were planted, not sometime previous to planting, as prescribed in 
the directions for the use of kainit. 

In Fittbogen's" field experiments with oats, which had been mixed in 
a gruel of superphosphate before sowing, the plot sown with candied seed 
yielded less than did that with unfertilized seed. If, on the other hand, the 
superphosphate was diluted with sawdust, the yield was the heaviest of all. 
Probably the sulfuric acid hydrate which often appears, together with 
phosphoric acid hydrate, also acts injuriously in direct contact with the 
superphosphate. Briigmann'* also reports on the injurious action of fer- 



1 Tautphfpus. v., Die Keimung- der Samen bei verschiedener BeschafCenheit 
derselben. cit. Bot. Jahresber. 1876, II, p. 117. 

2 Beobachtungen liber den schadllchen Einflufs der Kainit- und Superphosphat- 
diingung- auf die Keimfahigkeit der Kartoffeln. Biederniann's Centralbl. 1880, p. 765. 

3 Deutsche landwirtschaftl. Presse 1877, No. 81. 

4 Hannover'sclie landwirtsch. Zeit. 1881, No. 12. 



389 

tiliers made soluble by sulfuric acid. This action was very evident in dry 
springs, and, in fact, on v^dieat as well as on other cultivated plants. 

In seeds, the injurious effect of the "candying" will be the less felt the 
longer the seed lies in the sojl, before sprouting, for then frequent rains can 
wash more of the fertilizing salt into the surrounding soil. This has been 
demonstrated in earlier experiments in Salzmunde\ 

Over-Fertilized Beets. 

Common experience with present intensive beet cultivation, shows 
that an increased nitrogen supply increases the harvest in bulk, but reduces 
the sugar content. For this reason we will give only one proof that shows 
the importance of the form in which the nitrogen is applied. PagnouP 
analyzed three beets, of which the first (H) had been watered several times 
with a solution of (commercial) nitrate of soda; the second (J) with 
ammonium sulfate; while the third (K) represented a normal beet, har- 
vested at the same time. 

H. J. K. 

The harvest weight amounted to 4i45g 26/Og ySsg 

Density of the sap amounted to 1.026 1.040 1.046 

Percentage of sugar in the beet 

substance amounted to 3.9 6.3 8.3 

CO2, and Chloral alkalies in 100 

parts beet substance amounted 

to 1.991 0.924 0.814 

The amount of these in 100 parts 

sugar is 28.0 14.6 9.8 

It is evident that with nitrogen fertilization the amount of fresh sub- 
stance harvested has increased three and a half to five times that obtained 
with normal cultivation, but the sugar percentage has fallen to one-half. 
The comparison of the effect of the nitric nitrogen with that of am- 
moniacal nitrogen is especially interesting. Mention was made above that 
the latter gives rise to a considerably greater ammonium content in the beet 
substance. 

Miiller-Thurgau's recent experiments" show that the nitrogen fertiUzed 
plants have a heightened respiration, which may well be the result of a 
heightened conversion of cane sugar into the directly reducing sugar. On 
an average every 6 beets contained 

Sugar, directly reducing, Cane sugar 
Beets rich in nitrogen 0.34 per cent. 8.27 per cent. 

Beets poorer in nitrogen 0.04 per cent. 14-39 P^r cent. 

An idea of the processes which are initiated by a superabundant nitro- 
gen supply may be obtained from the statements of Pfeiffer-Wendessen*, 

1 Jahresber. f. Agrikulturchemie 186.3, p. 60. 
~ Annules agronomiques 1876, p. 321. 

3 s. tJberdiingte Kartoffeln. p. 390. 

4 Bericht liber die Genei^alversammlung d. landwirtschaftl. Centralver. f. d. 
Herzogtum Braunschweig. Blatter f. Zuckerrubenbau 1896, No. 8. 



390 

who is of the opinion that in any case the nitrogen is transformed into 
proteins, which, in combination with calcium, are decomposed into asparagin, 
glutamin and corresponding organic salts. These form soluble salts with 
calcium, which in turn are found again in the sugar extractives, etc. 
Schultze also characterizes the incompletely utilized, intermediary nitrogen 
compounds as essential constituents of the syrup which impair the crystal- 
lization of the sugar. In the plant itself, as in sugar manufacture, the com- 
pounds here named may retard the precipitation of the sugar, and thus 
explain the condition of unripeness and of small sugar content in the over- 
manured beets. Besides the delay in ripening, the beets do not keep well 
when stored in piles. Phosphoric acid improves the quality; the juice of 
beets, which had been over- fertilized with phosphoric acid and badly 
polarized, contained the fewest elements which prevent the crystallization 
of the sugar. 

Good and bad experimental results have been obtained from top 
dressing chiefly with Chile saltpetre. This condition is observed in almost 
all experiments. Besides the quantity used, the result depends also on the 
way in which the plant utilizes the fertilizer. This differs greatly according 
to the variety, the density of the soil, the way it is worked, the locality and 
the weather. Reference should be made to Kuntze-Delitsch's^ observations 
on top dressing. He found that the soil easily forms a crust, causing the 
young beets to die in spots because of a lack of oxygen, while the older 
ones develop poorly. In any case, fertilization with Chile saltpetre should 
be followed immediately by harrowing-. 

Opinions differ as to the advisability of using nitrogen fertilizers with 
seed beets. While it is asserted by some that the quality of the strain de- 
clines, Wilfarth^, on the strength of his experiments, contradicts this 
statement. 

Over-Fertilized Potatoes. 

The effects of over- fertilizing potatoes with nitrogenous fertilizers are 
the same as for beets. Miiller-Thurgau's^ results show for both that an 
abundant nitrogen fertilization causes a stronger leaf development with a 
greater chlorophyll content. At the same time, the formation of starch is 
impeded; the starch is more rapidly dissolved in the leaves, and smaller 
quantities are stored. The organs show a greater glycose content, the re- 
serve substances are more rapidly dissolved, the nitrogen compounds are 
more extensively transformed, while respiration is heightened and growth 
increased. 

A poorer keeping quality of the tubers is correlative with a lesser supply 
of reserve substances and their more rapid consumption in respiration. 



3 cit. Zeitschr. f. Pflanzenkrankh. 1896, p. 310. 

2 The action of the perchlorate in the use of Chile saltpetre will be discussed 
under the section on Injurious gases and liquids. 

3 Wilfarth, H., Wirkt eine Stickstoffdungung der Samenriiben schadlich usw. 
Zeitschr. d. Ver. Deutsch. Zuckerindustrie. Vol. 50, Part 528, p. 59. 

■1 Miiller-Thurgau, Dritter Jahresbericht des ptlanzenphysiol. Laboratoriums d. 
Versuchsstat. Wadensweil. Ziirich 1894, p. 52. 



391 

But an excess of nitrogen directly promotes decay, while that of calcium 
phosphate has an opposite effect. I planted in sandy soil, in alternating 
rows, pieces of healthy tubers from three varieties as different as possible 
and also pieces from tubers suffering from black dry rot^. This field was 
divided into two halves absolutely similarly planted, of which one was given 
large amounts of Chile saltpetre on all the rows, the other Thomas slag. 
In the healthy seed, in the half fertilized with Qiile saltpetre, the tubers 
sprouted very imperfectly while almost all the diseased seed had decayed. 
The results obtained in the plot fertilized with Thomas slag were directly 
opposite. There the diseased seed yielded very uniform healthy plants. 

In the last named plot, plants from healthy and diseased seed of all 
varieties developed shorter shoots with more highly colored foliage. They 
ripened more rapidly and the harvest was nearly twice as large as from 
the plot fertilized with Chile saltpetre-. 

With this might be associated also the phenomenon well-known in 
practical circles as iron spottedness or the multi-colored condition of pota- 
toes. Tubers outwardly normal have brown or brownish-gray places in 
their tissue in the fresh cross-section. In this, the rest of the flesh can be 
perfectly healthy and remain white, or, exposed to the air, may quickly 
assume a rusty red color. The spots originally discolored have brown, 
dead cell walls and many still contain starch. Often, and, in fact, when 
the cut surface subsequently turns red in the air, only traces of starch may 
be found in the diseased centres, but sugar is found instead. 

While some observers think the iron spottedness must be traced to an 
abundance of acid iron compounds in the soil, others are inclined to be- 
lieve dampness to be the cause. Many discoveries show, however, that 
heavy fertilization with stable manure caused the iron-spotted condition in 
certain varieties, which, in the same year, with chemical fertilization, re- 
mained healthy^. Tubers which turn red, when cut, are found most fre- 
quently where an abundant nitrogen fertilization is used. Hence one is 
justified in considering a multi-colored condition of the flesh to be an indi- 
cation of nitrogen over- fertilization. Tubers with iron spots, as a rule, 
yield healthy plants in the following year. 

Chile Saltpetre With Woody Plants. 

Janorschke* has investigated the phenomena of nitrogen fertilization 
without the addition of calcium and phosphoric acid. He found that plants 
with multi-colored leaves became greener for the first year or two. In 
dwarf fruits the branches continued to grow almost without interruption 
until August and even later, which thus prevented the setting of the blossom 
buds. Attention should also be called to the fact that the effect of the fertilizer 



1 Zeitschr. f. Pflanzenkrankh. 1894, p. 12G, und 1895, p. 98. 

2 Zeitsch. d. Landwirtschaftskammer f. d. Prov. Schlesien 1899. 

3 s. Jahresberichte des Sonderausschusses fiir Pflanzenschutz, herausgegeben 
V. d. Deutsch. Landw.-Ges. 

4 Zeitschr. d. Landwirtschaftskammer f. Schlesien 18S8, No. 34. 



392 

on trees does net make itself felt until the year following its application, 
but then has a continuous action up to the third year. From my own ex- 
periments, in which sewage was used, I consider the increased tendency of 
the fruit to decay, especially when it begins at the core, as well as the greater 
susceptibility to frost, to be the effect of a one-sided, excessive nitrogen 
fertilization. Calcium phosphate counteracts this evil. Experiments with 
apple trees, abundantly fertilized with saltpetre, showed that the fertilized 
trees suffered more from aphids than did unfertilized trees\ 

The foliage of Ailanthus glandulosa growing in well-fertilized positions 
became yellow and the branches blighted. On the cut surfaces of fresh 
branches Penicillium developed abundantly. The sugar content of the 
tissue at this place was very great. 

In orange plantations, fertilized trees tended to gummosis and the dis- 
ease called "Die-back" in Florida is traced directly to over-feeding with 
organic nitrogenous compounds. These orange trees are said also to be 
more susceptible to insect attacks". 

Over-Fertilization of Vegetables and Other Field Crops. 

Although our vegetables, as a whole, in their present form, are the 
product of a high degree of cultivation, and have adjusted themselves to 
abundant fertilization, we still often find cases of disease due to over- 
fertilization, especially where sezvage has been used. There is a perceptible 
increase of the easily oxidizable substances which turn brown in the air. 
In this case, the walls of the ducts turn brown and, not infrequently, some 
of the ducts are filled with an inky fluid. Bacterial decay occurs frequently 
in over-fertilized plants. Peas and other Leguminoseae withstand least of 
all an excess of nitrogen while increased adaptation is found in some Um- 
belliferae, as celery for example. But even here the favorable amount is 
often exceeded in sewage bed cultivation. If the cut surface of fleshy 
root tubers becomes rusty, the tubers as a rule have lost in flavor. The 
more advanced stage, frequently found in vegetables shown in the markets 
of large cities, consists of an increased sponginess of the tissue and a greater 
brown spottedncss. Such conditions and the bacterial decay, connected 
with them, manifest themselves in cabbage plants accustomed to nutrient 
solutions of the highest concentration. Under such conditions it is ad- 
visable to add calcium phosphate and to cultivate continuously. 

Owing to the increased use of rhubarb stalks as a spring sauce, the 
plants are being cultivated on sewage beds. In such plantations I observed 
cases where the unusually thick stems were absolutely insipid. Thus a 
scanty production, or a complete consumption of the organic acids, is con- 
nected with over- fertilization. In my opinion this regression in the amount 



1 Fiinfter Jahresber. d. Grofsherzogl. Obstbauschule zu Friedberg i. d. W. 

2 Webber, H., Fertilization of the soil, etc. Yearbook U. S, Depart. Agric. 
for 1894. Washington 1895, p. 193. 



393 

of acid associated zvith an excess of nitrogen may also be sought elsewhere 
and may be the cause of the rapid appearance of bacterial decay^ 

In the Cucurbitaceae (cucumbers and melons) a concentration of the 
nutrient solution, not dangerous in itself, can act injuriously if the temper- 
ature is continuously too low. In this case gum appears most abundantly 
on the iruit and connected with it a blackening of the ducts is also noticed. 

In tobacco culture, an excess of nitrogen manifests itself in coarser 
leaves and a larger nicotine content-. 

Mention has been made of the fact that sewage fertilization of grain 
may cause lodging and sterility. 

ExcESSivB Nitrogen Fertilization for Decorative Plants. 

Very numerous cases of this may be found. Besides fertilization with 
sewage and Chile saltpetre, or ammonium sulfate, horn shavings are ex- 
tensively used, especially for garden plants. Naturally we can cite only a 
few examples. 1 gave a few plants of Begonia semperflorens an excess of 
ammonium sulfate. Four days after fertilization the young shoots became 
discolored at the base and began to drop. The edges of the leaves began 
to show dirty green areas which later became brown and dried up. These 
were connected with the healthy tissue at the centre of the leaf by 
a more transparent transitional zone. In the sun, the wilting became more 
rapid. The pith and bark were found to be filled with masses of calcium 
oxalate ; the individual crystals were not as sharp as those in healthy speci- 
mens but more rounded like tubers. No starch was present in the diseased 
tissues and the chloroplastids were reduced to small angular grains. 
The ducts were frequently filled with a brown, granular content. The cell 
walls of all the tissues were brown. The contents of the epidermal cells of 
the leaves were brown and granular. Before the decomposition of the 
chlorophyll grains, brown drops were often found in the contents of the 
mesophyll cells. 

In Begonias, as well as in Pelargonium sonale, the leaves discolor and 
fall off easily wnen dried. I found an unusual number of calcium oxalate 
crystals in the pith and young bark of the axes of diseased plants. The 
stems of the Pelargoniums contained in general fewer and smaller starch 
grains. They were almost entirely lacking in the bark parenchyma, while, 
in the over- fertilized plants, they were present in abundance. 

This is an example of the same phenomenon observed in potatoes and 
beets, — i. e., a poverty in carbohydrates. 

A slight fertilization with Chile saltpetre, given to freshly rooted Pelar- 
gonium cuttings at first caused a very luxuriant growth. Later, because of 
frequent repetition, the efifects became serious; — the leaves drooped, and 
brown decayed areas appeared on the stem just above the leaf bud. In a 
a short time these spots encircled the entire stem. Then the leaves fell and 



1 See Action of oxalic acid, p. 361. 

- Schellmann, W., Der Tabak und seine Nahrungsanspriiche. "Der Pflanzer." 
Herausg. Usambara-Post 1905, No. 5. 



394 

the whole aerial axis died back to a short stump. New, weak shoots then 
began to sprout. We have cited this example, in order to show that the 
effect of over-fertilization, although it takes place through the soil, does not 
make itself felt at first at the base of the axes but on the peripheral organs, 
the leaves. 

In comparative experiments with Fuchsia cuttings^, a continued fer- 
tilization with small amounts of ammonium sulfate resulted in a noticeable 
increase in growth and an enlargement of the leaves. The epidermal cells 
of the leaves had thinner walls and the wood ring of the branches made a 
weaker development. The starch content was smaller, the chlorophyll con- 
tent larger, the period of growth lengthened. When the fuchsias were 
protected from autumnal frosts, by being brought into a greenhouse, they 
had time to ripen normally, and the differences as compared with unfer- 
tilized plants disappeared. The fertilized ones had rather the advantage 
in a greater growth. Here we have a result such as is evident in growing 
fodder beets. The addition of large amounts of nitrogen retards the ripen- 
ing process. If the plants can reach maturity before frost, so that the leaves 
ripen normally, we obtain the desired results from fertilization, i. e., the 
production of greater amounts of material, with a normal supply of reserve 
substances. But, as a rule, the climatic conditions prevent the termination 
of growth and winter finds the organs in an immature condition. 

The disadvantage of harvesting insufficiently matured plants has been 
emphasized under "agricultural crops." Such plants have a greater tendency 
to decay. 

The same results were obtained with comparative fertilization experi- 
ments with Erica. The red blossoming varieties developed less vividly red 
or almost bluish red blossoms in the series of experiments with a one-sided 
nitrogen fertilization; their habit of growth was more drooping and the 
blossoms set less abundantly. The fertilized specimens suffered so greatly 
from Botrytis cinerea in winter that most of them died, while unfertilized 
plants of the same varieties from the same place came through the winter 
uninjured. Bluth- carried out an experiment which showed the effect of 
a highly concentrated solution of all the nutrient substances. The Ericas, 
in the second year of cultivation, were given continued supplies of a one- 
tenth per cent, solution of Wagner's nutrient salt. After ten to twelve days the 
leaves became a darker color and their growth stronger, but the plants 
showed a greater sensitiveness to the action of the sun and drought, in com- 
parison with many hundreds of unfertilized specimens of the same variety. 
The new lateral shoots of certain tender varieties (£. hiemalis, E. congesta, 
etc.) developed a drooping and often curved habit of growth. Hard 
needled varieties (£. hlanda, E. mediterranea, E. verticillata, E. mamniosa) 
retained their erect habit of growth but the buds set in a strikingly small 



1 Sorauer, P., Einfluss einseitiger Stickstoffdungung-. Zeitschr. f. Pflanzen- 

krankheiten 1897, p. 287. 

2 Zeitschr. f. Pflanzenkrankh. 1895, p. 186. 



395 

number, or not at all, while the branches continued growth. Here too, for 
the most part, the fertilized plants died during the winter from Botrytis. 
In other fertilization experiments, made with horn shavings on Ericas, 
there was a luxuriant leaf development at the expense of the blossom buds, 
but the fertilized plants, during the winter, showed no greater weakness. 

From the many instances which have come to my notice, I must state 
the frequent "failure of forced Lilies-of-the-V alley," as due to an excessive 
nitrogen fertilization. Chile saltpetre and ammonium sulfate are often 
used when the plants are grown for two years out of doors. 

The plants grow more luxuriantly and their very strong (mostly blue- 
tipped) "pips" (bud-cones) deceive the buyer; the formation of the in- 
florescences, however, is weak. Such plants force with great difficulty and 
frequently bear flower clusters in which some buds do not mature. Com- 
parative experiments made by Koopmann^ showed very interesting differ- 
ences in forcing. When kainit was used as a fertilizer in growing the 
plants, the flower clusters developed first and the leaves followed very 
slowly, — on the other hand, when ammonia was used the leaf growth w^as 
so luxuriant that the flower clusters were entirely hidden by the leaves. In 
general, potassium may be recommended as a fertilizer for Lilies-of-the- 
Valley. 

A. further injurious effect could be determined for Roses. I have be- 
fore me observations showing that tea roses, among others, Marfchal Niel 
and Nyphetos, grown indoors, drop their buds after heavy fertilization, or 
decay at the point where the calyx passes over into the stem. When dis- 
eased plants had been repotted in a sandy soil poor in nutrients, normal 
blossoms developed in the following year. I observed similar phenomena 
of decay in Bourbon and Remontant roses in the open after sewage fertiliza- 
tion. Here, an application of gypsum gradually decreased the disease. 

In other garden plants, even in ivy, I had opportunity to observe phe- 
nomena of decay after an excess of nitrogen (usually in the form of sewage 
fertilizers, liquid manure, Chile saltpetre and ammonium sulfate). In the 
majority of cases, I have recommended transplanting the plants into pure 
sand or a very sandy leaf loam for a year and have tried it myself repeatedly 
with good results. 

Leaf Curl of the Potato. 

We will include here this disease so well-known to potato growers and 
so often studied scientifically; the causes of which, however, are still un- 
known. The reason for considering leaf curl here is the deduction from 
my observations that diseased shoots show characteristic evidences of one- 
sided nitrogen fertiUzation. Direct results are not involved here, only the 
after effects in the following year. The parent tuber is either immature in 
a few eyes, or entirely so. In the following year a diseased condition de- 
velops in all of the shoots or only in some of them. This limitation of the 



1 Zeitschr. f. Pflanzenkrankh. 1894, p. 314. 



396 

attack is to be emphasized, because, at times, up to the present, observers 
have emphasized especially that all the stems on a tuber become diseased, 
i. e.' that the cause of the disease must lie in the whole tuber, while my 
observations have shown beyond question that the diseased condition may 
be limited to a few eyes. 

According to Kiihn^, the disease appeared as an epidemic first in 1770 
in England and in 1776 in Germany, causing extraordinary losses. The 
first symptom is the discoloration of the leaves which no longer have the 
fresh appearance of healthy plants. The main leaf stem is usually found 
bent downward or completely rolled up; the various leaflets are folded, 
curled here and there and covered with brown, usually longish spots. The 
latter extend as far as the main rib of the leaf and finally to the stem. At 
first only the superficial cells are brown, later the disease extends deeper 
into the tissue, even to the pith of the stem. This changes the consistency 
of the stem from a normal flexibility to a glassy brittleness. In addition, 
according to Schacht, sugar is found very abundantly in the diseased cells-. 
If such plants live until harvest time, they either set no tubers at all or only 
a very few. 

In the earlier literature, very different causes (including parasitic 
fungi) are given, as shown by reference to the previous edition of this 
manual. Newer theories may be found in Frank's^ study. He distinguishes 
a number of different forms of the disease and, agreeing with me, states 
that the very beginnings of the diseased condition do not show any fungous 
action. The cause of the death of the protoplasm in the various brown 
tissue centers is not known. Differing from my observations, however, 
Frank emphasizes "that all the shoots of a plant became sick simul- 
taneously*." 

In making more extensive cultural experiments, using several varieties, 
and directed especially to the study of leaf curl, I found that the phenom- 
ena of disease appeared initially only in one variety {Early Puritan). The 
diseased plants, scattered among the healthy ones, made only a third as 
much growth and showed the well-known characteristics, especially the 
breaking of the curled leaves. Small corky fissures were often found on the 
petioles. The first stages of the disease on the stems were found in one of 
the internodes below the surface of the soil, where a blackening of the duct 
walls could be determined. This characteristic can be traced back, radiating 
more or less deeply into the tuber which otherwise seems healthy. This 
shows that the tuber has not carried the disease to the shoot but, conversely. 
In the same way, the browning of the ducts radiates out from the diseased 



1 Kiihn, Jul., Krankheiten d. Kulturgewachse. 1858, p. 200. — Ber. aus. d. 
physiolog. Laborat. d. landwirtsch. Instituts zu Halle. 1872, Part 1, p. 90. 

y Bericht an das Kgl. Landesokonomiekollegium liber die Kartoffelpflanze und 
und deren Krankheiten. 1854, p. 11. 

3 Frank, A. B., Die pilzparasitaren Krankheiten der Pflanzen. Breslau 1896, 
p, 300. — Kampfbuch gegen die Schadlinge unserer Feldfruchte. Berlin, Parey, 
1897, p. 217. 

4 Kampfbuch p. 222, 



397 

stem node into the roots, produced at that point, and may be found in the 
whole part of the axis which is still green, up to the ribs of the last leaves. 

Especially striking is the sap turgescence in the apparently perfectly 
healthy parent tuber which exhibits some cells with large unconsumed starch 
grains. The groups of cells containing the starch lie scattered in the very 
turgescent parenchyma of the tubers, which shows scarcely any traces of 
solid cell contents, while the nuclei are large. 

It is further noteworthy that, just as healthy and diseased shoots may 
be produced from one tuber, the characteristics of disease on the same stem 
can often be restricted to definite areas. Healthy eyes may develop on 
diseased stems and diseased stems, are found in which only half of the vas- 
cular bundle ring is blackened. 

Thus, like other diseases connected with the discoloration of the ducts, 
leaf curl begins to manifest the first symptoms of disease at the periphery. 
The cuticle blackens most of all. The cell contents began to change color 
at first to a weak inky color, until the walls and contents have become uni- 
formly brown, after which the epidermal cell collapses. 

Where the epidermis borders on the coUenchymatous tissue, the dis- 
coloration advances in its walls. They become slightly yellowish at first, 
then reddish yellow (in some varieties a peculiar blood red), and finally 
brown. This discoloration of the walls, which seems to spread rapidly 
tangentially, recalls enzymatic activities. 

The further course of the disease diiifers in the difi^erent varieties, 
probably because the cell walls vary in construction, some being more loose- 
ly built, others more solidly. In F.arly Puritan it was observed that the 
browned cell walls could be attacked by a granular decay, in which small 
rod-like bacteria probably participated. In these cases the tissue disap- 
peared, while holes and depressions appeared in the bark tissue of the 
stem and mycelium was found. In Early Puritan the depressions deepened 
to the wood ring and, as the disease advanced, their pressure could be dem- 
onstrated even on the still green tips of the stems. The browning of the 
ducts, however, did not proceed from them ; it began at the base of the 
stem and spread only in the vascular system. At the torn places processes 
of healing often manifested themselves in the pouch-like elongation of the 
adjacent, healthy bark parenchyma cells. 

The statement given above, that the symptoms of disease do not uni- 
versally appear uniformly relates, for example, to the appearance of hrozvn 
specks on the uncurled leaves. However, in the petioles of these leaves 
there is exactly the same pale inky filling of the ducts which, in some cases, 
thickens to a grainy slime ; the walls of the ducts also are browned. 

The characteristics here described occur separately also in other plants 
with an excess of nitrogen. If these symptoms are compared with the re- 
sults of earlier observations, leaf curl may be described as follows. The 
diseased condition appears most luxuriantly and abundantly on tender early 
varieties. The harvested tubers are immature, being distinguished by a 



398 

smoother skin, a lower starch content and a considerably higher potassium 
content. They are also smaller in size and have a smaller dry weight. Under 
favorable conditions, healthy plants may often be grown from such tubers. 

Among the characteristics given, we have emphasized the length of the 
existence of the parent tuber, which remains turgid and retains starch, 
because Hiltner^ has recently described such a case belonging here and, in 
fact, a partial subsequent enlargement of the parent tuber. Different people 
have made the same observations. In Hiltner's case it was also observed 
that the plants produced from the turgid tuber developed no tubers below 
the soil, attached to the stolens, but bore them directly on the lower inter- 
nodes of the green stems. These stems, however, were only half as long 
as in normal plants and bore leaves, rolled together, which reminded Hiltner 
of leaf curl. He thinks that these processes are a result of the use of im- 
mature tubers for seed. These tubers, after developing the stem, had uti- 
lized in their own further growth the material obtained by the action of 
the leaves. Naturally too little organic substance remains for the tubers of 
the current year. 

If we accept Hiltner's theor}' as to the production of tubers which re- 
main turgid, we can infer that leaf curl results from the use of unsuitable 
seed. The tubers were not sufficiently matured in the previous year. This 
must also make itself felt in the full development of the individual eyes. 
While the majority of these had time to develop normally, some may have 
remained immature and have retained this character when sprouting in the 
following year. This will explain the fact that often only isolated shoots 
are found which show leaf curl. The characteristic of immaturity is the 
marked abundance of potassium and nitrogen compounds with a scanty 
deposition of carbohydrates as reserve substances. We find such conditions 
favored by the use of fresh manure with early varieties and drought stops 
the growth of the tubers prematurely. 

If an over-supply of nitrogenous compounds, not normally utilized, 
determines the appearance of leaf curl in the potato, the shrivelling disease 
of the mulberry tree, and other diseases, to be mentioned under "Enzymatic 
Diseases," then the symptoms of the blackening of the ducts and rapid 
bacterial infection, already found, may be explained easily. 

This theory is further supported by a study made by Appel-, who, under 
the name "Bacterial-ring disease/' describes the phenomena which often 
suggest leaf curl. He makes bacteria responsible for the ring disease 
and "indeed, as in black-leg, not one species alone but a few closely re- 
lated forms." "These bacteria are undoubtedly present normally in many 

soils " Influenced by these statements I should like to Include 

bacterial ring disease under those diseases in which a constitutional weak- 
ness in the plant and not a parasite determines the phenomenon and favors 



1 Hiltner, L., Zur Frage des Abbaues der Kartoffeln. Prakt. Bl. f. Pflanzen- 
bau und Pflanzenschutz 1905, Pai't 12. 

2 Appel, O., Die Bakterien-Ringkrankheit der Kartoffel. Flugrblatt 36 d. Kais. 
Biolog. Anst. Dahlem. 1906. 



399 

especially the spread of the bacterial infection. These conditions are simi- 
lar to those described as leaf curl, in which I likewise have observed decom- 
position of the tissue b)^ bacteria. 

It thus seems that we have before us a whole group of potato diseases, 
with the common characteristic that the ducts turn black. This may be 
traced to the fact that incompletely consumed nitrogenous compounds make 
their influence felt in an insufficient development of the carbohydrates. 

We must seek to overcome this condition to the best of our ability by 
fulfilling the requirements for a gradual, complete ripening of the tubers 
on the plant. 

d. Excess of Calcium and Magnesium. 

In addition to the observations on the use of lime as mentioned in 
earlier sections, we will emphasize here first of all Orth's^ warning that it 
should be supplied to the field in small, frequent doses rather than in one 
heavy application. 

Of course, an excess of calcium cannot be determined exactly by defi- 
nite figures, since the demand of each plant and each field is diflferent. Also, 
in adding the lime it does not depend at all on the absolute amount of cal- 
cium supplied but on the proportion to the other nutrients of which the 
calcium influences the solubility and capacity for transportation. Finally, 
the weather conditions at the time the lime is applied must be considered. 

Hofifmann-, from his broad experience, has given many warnings which 
are of utmost value practically. Calcium is injurious when used in large 
amounts on exhausted soils. On lighter, active soils, poor in humus, during 
dry springs, it loosens and dries the soil too much and disturbs the bacterial 
action. If it is used in the form of marl, it must first be well decomposed 
in the air, in order that possible injurious elements can be oxidized at the 
right time. Calcium acts detrimentally in continued drought, and also with 
stagnant water if it, in the form of so-called "water-lime," is mixed with a 
good amount of silicic acid, ferric oxide and clay. In wet weather, it be- 
comes as hard as cement. 

But even under normal conditions, calcium may be detrimental. We 
must not forget that, together with the desired efifect of decomposing organic 
substances, containing nitrogen, and of transforming the ammonia produced 
into calcium nitrate, ammoniacal compounds are set free. If ammonium 
nitrate or ammonium sulfate is mixed with calcium carbonate or phosphate, 
it produces the very soluble calcium chlorid and g\^psum and ammonium 
carbonate or phosphate. In Wagner's^ experiments (Darmstadt), the loss 
of nitrogen, produced by the volitalization of ammonia, was observed to be 
30 per cent, of that in a fertilization with nitrate. The same losses are pro- 
duced very easily, if the soil is rich in calcium carbonate, if the ammonium 



1 Orth, A.. Kalk- und Mergeldiing-ung-. Anleitung, im Auftrage d. Deutsch. 
Landw.-Ges. Berlin 1896. 

2 Hoffmann, M., Diingungsversuche mit Kalk. Arb. d. D. Landw.-Ges. Part 106. 

3 Zeitschr. der Landwirtschaftskammer f. d. Prov. Schlesien. 1904, p. 1683. 



400 

salt is only superficially worked in so that the sun and wind have abundant 
access to it. Then the free ammonium carbonate, produced by the trans- 
formation of the fixed ammonium sulfate, can be removed from the field 
very quickly. 

Sandy soils, which at the time are rich in calcium, are on this account 
not suited for an ammonia fertilization, especially not as a top dressing. 
This explains why quick lime should not be brought directly into contact 
with stable manure or other ammonium fertilizers. 

Besides these reactions, lime also acts on phosphoric acid. This action 
must not be underestimated. The action of the phosphoric acid on super- 
phosphate, which is soluble in water, is impaired by the simultaneous use 



Superphosphate 



Lime 



Ammonium 
sulfite 



Potassium 




Tliomas slag 



Stable manure and 
guano 



Kainit 



Chile Saltpetre 



Fig. CG. Diagrammatic repi-esentation of the favorable and unfavorable mutual 
relations of fertilizers to each other. 

of lime ; but not so much so as the phosphoric acid in Thomas slag, soluble 
in citric acid. The destructive efifect of lime on phosphoric acid is greatest 
when used with ground bone. 

It may be the place here to refer to the mutual relation of fertilizers in 
order to avoid using them in such a way as to impair their action. Instead 
of more lengthy descriptions we will reprint a figure borrowed from the 
"Practical Advisor in Fruit and Garden Culture," 1906, No. 17^ 

In this diagram, the thin connecting lines signify that the various kinds 
of fertilizers may always be mixed together. The fertilizers, which appear 
connected by double lines, may be mixed with one another only very shortly 
before spreading; while those fertihzers connected in the figure with thick 
lines may never be mixed together. 



1 "Praktischen Ratgeber im Obst- und Gartcnbau." No. 17, 1906. 



40I 

The poisonous effects of an excess of magnesium and the associated 
theory given by Loew, as to a definite quantitative relation between calcium 
and magnesium in the soil for obtaining good harvests, have been con- 
sidered already in the section on "Lack of Calcium" (p. 301). Recently 
Loew^ has supplemented his earlier statements by calling attention to the 
fact that the favorable quantitative relation between calcium and mag- 
nesium in the soil cannot always be fixed by definite figures. It changes as 
soon as the two bases are made accessible in different degrees for absorp- 
tion by the plant. 

Loew's theory is contradicted by experiments made by Meyer-. The 
emphatic fact here is that heavy additions of calcium as well as of 
magnesium can greatly impair the yield. Naturally the various plant species 
behave very dift'erently with the same fertilizer. Given the same quantity 
of magnesium, the grain and straw yield of oats was lessened, but that of 
rye was not decreased. 

GosseP, on the basis of his own experiments, also considers Loew's 
point of view to be incorrect, yet we think it, nevertheless, worth consider- 
ation. Too much faith must not be put in definite figures because each 
cultural experiment offers different conditions. A constant effort must be 
made to overcome the injurious effects of the magnesium compounds when- 
ever brought into the soil in great quantities in the fertilizer. Of first im- 
portance is the great quantity of magnesium chlorid spread on the field with 
the so-called "waste salts" which reduces the sugar content of beets, the 
starch content of potatoes, etc. An effort must be made to combine th'e non- 
absorbable chlorine with a base, especially calcium, so that it can be washed 
easily into the subsoil. 

Finally attention must be called to the fact that the same amount of 
calcium acts injuriously at one time and beneficially at another, according 
to whether it is added in the forms of calcium carbonate or calcium sulfate. 
Thus, for example, Suzuki*, found in vegetative experiments with moun- 
tain rice, that the yield was considerably reduced by an excessive ad- 
dition of calcium carbonate (the proportion of calcium to magnesium was 
as 3:1), even if phosphoric acid was present in an easily soluble form. On 
the other hand the addition of an equivalent amount of gypsum caused an 
unusual increase in the yield, especially of grain. From this experiment, 
however, it is evident that the injurious action of an excess of calcium is not 
always to be sought in a decrease in the looseness of the soil as compared 
with that found after the use of slightly soluble phosphoric compounds, but 
probably has its foundation also in the neutralization of the root acids. 

1 Loew. O., and Aso, K., tjber verschiedene Grade der Aufnahmefahig-keit von 
Pflanzennahi-stoffen durch die Pflanzen. Bull. College of Agric. Tokyo. Imp. Univ. 
Vol. VI. No. 4, cit. Centralbl. f. Agrik.-Chemie 1905, p. 594. 

2 Meyer, D., Untersuchungen iiber die Wirkung verschiedener Kalk- und 
Magnesiaformen. Landw. Jahrbticher Vol. XXXIII, 1904, p. 371. 

3 Gossel, Fr., Bedeutung der Kalk- und Magnesiasalze fiir die Pflanzenernah- 
rung. Vortrag auf d. 75. Naturf. Vers. (s. Cliemikerz. 1903, No. 78). 

4 Suzuki, S., tJber die schadliche "Wirkung einer zu starken Kalkung des 
Bodens. Bull. College of Agric. Tokyo, Imp. University. Vol. VI. cit. Centralbl. 
f. Agrik.-Chem. 1905, p. 588. 



402 

By neutralizing the acids of the plant routs the available phosphoric 
acid will not be so largely absorbed. The great difference between the 
action of calcium carbonate and that of gypsum is due to the fact that 
gypsum is taken up from the soil only so far as it is soluble in water (i. e. 
in the very sUghtest amounts), while the absorption of the carbonate by the 
plant depends upon the carbonic acid of the root. 

Excess of Calcium With Grapes. 

Since the introduction of grapes grown on budded American vines 
there have been very many complaints of Jaundice. The disease is de- 
scribed usually as "Chlorosis" ; but according to my conception it must be 
called "Icterus." 

Of course, the causes of the yellow condition of the foliage of grapes 
may differ very greatly, as in other plants. Very frequently, root decay, 
occurring with or without fungi, plays a role in heavy soils. Vitis Riparia 
and V. rupcstris, with their weaker root systems are especially sensitive to 
such soils, while varieties with strong roots (Jacquez, Herbemont, etc.), 
better adapt themselves^. American vines, however, are grown with great 
difficulty on soils containing a great deal of calcium in an easily soluble form 
and not rich in nutrients. In France it was possible to collect the greatest 
amount of information on this subject. Luedecke- repeats the results of 
soil investigations which the agricultural society of Cadillac undertook in 
1890. The soil which showed no jaundice of the vines and that which 
showed jaundice contained 

No jaundice jaundice 

Phosphoric acid 0.07 per cent. 0.06 per cent. 

Potassium 0.39 per cent. 0.37 per cent. 

Calcium 1.81 per cent. i8-93 per cent. 

Ferric oxid 5.90 per cent. 3.02 per cent. 

Nitrogen o.io per cent. o.io per cent. 

The content of both soils in nitrogen, potassium and phosphoric acid, 
therefore, is about equal ; the ferric oxid percentage is high in both, but 
the calcium is nearly ten times as great in the soil producing jaundice. In 
the fertilization experiments undertaken with Chile saltpetre, ammonia, 
superphosphate, potassium chlorid, magnesium sulfate and iron sulfate 
(ferric sulfate), only the last gave any satisfactory results. In this ex- 
perimental plot, the vines formed a great many new roots. The same re- 
sults were again obtained under similar conditions on soils naturally rich 
in iron, in which, therefore, the favorable action of fertilization with iron 
sulfate cannot be ascribed to a previous lack of iron. 



1 Eg-er, E., Untersuchungen liber die Metlioden der Schadlingsbekampfung 
usw. Berlin, Paul Parey, 1905. 

2 Luedecke in Zeitschr. f. d. landw. Ver. d. Grossherz. Hessen 1892, No. 41, 
1893, No. 2. 



4<>3 

Such results, proving that jaundice of the grape is due to a high calcium 
content are found^ frequently as are also observations as to the efifectiveness 
of the iron sulfate. 

The question now is, how to explain the injurious effects of calcium 
and the beneficial action of the so-called iron compounds. Luedecke found 
that the water coming from the lime soils of Rhenish Hessen has an alkaline 
reaction, and he found that with an addition of some iron salt (iron stilfate 
or ferric chlorid), the iron was precipitated. He, therefore, came to the 
conclusion that, since plants are able to take up iron only in a dissolved 
form, and since the alkaline water prevents its solution, the grape vines 
suffer from a lack of iron in spite of the great amount of it in the soil ; they, 
therefore, become icteric. Viala and Ravaz noticed the injurious action of 
lime in a neutralization of the cell sap of the roots". 

i Until we have the results of further experiments, we must be satisfied 
with the fact that large amounts of easily soluble calcium compounds will 
produce icterus of the grape, and that abundant additions of iron sulfate 
have often been found to be useful in combatting it. It is now of the first 
importance to consider that the affinity of the sulfuric acid of the iron com- 
pound for calcium is great and forms g^^psum which, only slightly soluble, 
is proved to be non-injurious, or even beneficial to growth. 

Eger=^ cites Oberlein-Beblenheim's experimental resuhs, showing that, 
on rich soils, fertilization with gA'psum considerably increases the yield. 
Since the addition of gypsum, made at the same time to poor soils, remains 
absolutely without result, the favorable action of the gypsum may probably 
be ascribed to its power of loosening up the soil. 

e. Excess of Potassium. 

Reference has been made already to the danger to soil constitution of 
a continued heavy potassium fertilization, and in this it was emphasized 
that lighter soils and moor soils responded more favorably to the addition 
of potassium. Recently, however. Hollrung has called attention to another 
disadvantage of all fertilization with mineral salts.— therefore, of potassium 
salts also. He refers to Hall's experiments, showing an absolute change in 
the water conditions in the soils. Hall determined (after 1866) the num- 
ber of days in one year in which drainage flowed from an unfertilized field, 
as contrasted with one constantly fertilized with Chile saltpetre. The 
longer the drainage flows, the more water is removed from the field. Al- 
though the results fluctuated in the several periods of five years each, which 
he compared, yet as a whole for the entire length of time, they indicated 
that in the "salted soils," larger amounts of water had passed into the 
drainage through the subsoil. This makes possible conclusions as to an 
unfavorable transformation of the soil. 



1 See V. Babo and Mach, Handbuch des Weinbaues and der Kellerwirtschaft 
(s. Eger). 

2 See Eger. 

3 Loc. cit. p. 84. 



404 

The effect of potassium salts on the plant depends on the form of the 
fertilizing salt and the soil on which it is used^ The question arises here 
as to the part played by the accessory salts incorporated in the soil with 
the addition of potassium. At present, kainit and the 40 per cent, potas- 
sium salt are used more extensively, ^^^ith kainit, 3^4 cwt. should be used 
if one desires to add as much potassium as is present in one cwt. of 40 
per cent, potassium salt. Among the accessory salts introduced in the 
kainit, sodium chlorid plays a prominent role. Besides this, magnesium 
sulfate and magnesium chlorid come under consideration. The individual 
plants behave very differently with sodium chlorid. Its effect on sugar 
beets is very good, but potatoes are very^ sensitive to it". The results with 
sugar beets, however, are rather deceptive. According to Aducco and 
AVohltmann's experiments, the amount of beet substance harvested is in- 
creased, but the quotient of purity and the sugar content are reduced. 

On account of the accessor}^ salts, Schneidewind and Ringleben^ tested 
raw potassium salts with different potassium compounds as contrasted with 
the highly concentrated forms. It was shown for a mixture of clover and 
grass, and for oats, sugar beets and potatoes, that kainit was superior to 
potassium chlorid and potassium sulfate, if sufficient amounts of calciimi 
carbonate were present. If these were lacking, opposite results were ob- 
tained. If the slightly soluble gypsum was used, instead of calcium car- 
bonate, kainit proved to be especially injurious for the mixture of clover 
and grass, but less so for oats. In potatoes the action was favorable if the 
soils were poor in potassium. With an increase of potassium, the effect of 
excess became evident, i. e. the starch content was lowered. Szollema^ 
found that the decrease of starch, effected by the chlorid, which is connected 
with a greater abundance of water, was somewhat greater in the varieties 
of potatoes naturally rich in starch than in those poor in starch. 

When plants are very sensitive to the chlorine compounds of the raw 
potassium salts, as, for example, kainit, the loss of potassium by its partial 
leaching from the soil during the autumn and winter, is really an advantage 
in so far as many of the dangerous accessory salts (sodium chlorid and 
magnesium chlorid), are washed out at the same time; therefore, while 
actually less potassium remains in the soil, it becomes more effective, be- 
cause it is in a purer form. This leaching of the potassium must be taken 
into consideration in soils with only small amounts of calcium and other 
such absorbents, as, for example, in light, sandy, and moor soils^ 

Concerning the disadvantageous eft'ects of potassium fertilization on 
cultivated plants, other than those already named, we will mention further 

1 Blatter fiir Zuckerriibenbau 1905, p. 62. 

- Blatter fiir Zuckerriibenbau 1905, p. 89. 

3 Schneidewind, W., and Ringleben, O., Die Wirkung- der Kalirohstoffe und 
der reinen Kalisalze bei ver.schiedenen Kalkformen. Landwirtsch. Jahrib. 1904. 
Vol. XXXIII, p. 353. 

■4 Szollema, D., tJber den Einfluss von Chlor- und anderen in den Stassfurter 
Rohsalzen vorl-commenden Verbindung-en etc. cit. Centralbl. f. Agrikultur-Chemie 
1901. p. 516. 

5 Schneidewind, Auswaschen des Kalis im Winter, Zeit-schr. d. I^andwirtschafts- 
kammer f. Schlesien 1904. No. 14, p. 471. 



405 

the effect on Tobacco observed by Behrens\ His experiments showed 
that the water content of the leaves increased considerably if potassium 
sulfate was added to stable manure and that this hastened greatly the decay 
of the leaves which dry with difficulty in the air. This probably is con- 
nected with the increase in turgor observed by Copeland, which is due to 
potassium salts (Potash). Sodium salts (soda) did not show this physi- 
ological reaction-. 

The complaint of farmers that continued potassium fertilization re- 
duces fhc quality of pasture plants so that animals fed with such hay, 
grow thin, should be considered here. Even if the statement that this ex- 
cessive action occurs is still contestible, nevertheless it is true, that a de- 
crease in flavor has been observed in the hay from fields repeatedly fertilized 
with kainit, or with kainit and Thomas slag^. 

The injuries appearing in different field crops and fruit trees are gen- 
erally the result of an unexpedient use of potassium salts, a practice often 
followed by serious injurv'*. These will best be prevented by not using 
potassium in large amounts on heavy soils, by not spreading the salt with 
the seed, by repeated, smaller applications of potassium and (in plants 
especially sensitive to chlorine, as, for example, potatoes) by the use of the 
40 per cent, potassium salt, and of other purified, highly concentrated com- 
pounds, instead of the commercial salts. 

The frequent use of potassium in small quantities is often beneficial 
because the calcium in the soil water, containing carbon dioxid, will be 
more easily leached out the more potassium salts are added to the soil, since 
the calcium is converted by them into soluble compounds. Hoffman^ 
recommends the use of a high per cent, commercial marl, where possible, 
and its application in at least 5 to y^A double centner*' per acre. If the 
soil is liable to become encrusted {"he baked"), at least 2^4 double 
centner of quick lime should be turned under superficially in the autumn 
and repeated possibly four years later. 

f. Excess of Phosphoric Acid. 

Injuries due to an excess of phosphoric acid are rare. They can only 
be expected where superphosphates are used abundantly, i. e. where some 
phosphoric acid, soluble in water, is present. The phosphoric acid of 
Thomas slag, soluble in citric acid, is less mobile. However, even the phos- 
phoric acid, soluble in water, passes over immediately into an insoluble 
form since the di-phosphates of calcium, magnesium, aluminum and iron 
formed in the soil, are dissolved only very slowly by the carbon dioxid of 



1 Behrens, J., Weitere Beitrage zur Kenntnis der Tabakspflanze. Landw. 
Versuchsstationen 1899, p. 214. 

2 Bot. Jahresber. 1897, I, p. 72. 

3 Mitteilungen d. Deutsch. Landw. -Ges. vom 11. Marz 1905. 

•t Clausen, Resultate von Obstbaunadungungen. Landwirt.schaftl. Jahrbiicher 
Vol. XXXin. p. 939. 

3 Hoffmann, M., Die Kalisalze. Anleitung. Herausg. v. d. Deutsch. Landw. 
Gesellsch. 3d ed., 1905. 

« A double centner equals 220 lbs. 



4o6 

the soil and the acid secretions of the roots. Injury from superphosphates 
is, therefore, to be feared even with heavy appUcations only on soils which 
are poor in calcium, iron and aluminum carbonates. There are only a small 
number of experiments on this subject. The careful investigations, made 
at the experimental station in Bernburg, on sugar beets^ fertilized with the 
monobasic calcium phosphate, i. e., excess of phosphoric acid soluble in 
water, have shown that the sugar content does not decrease and also that 
the amxounts of beet substance and non-sugar have remained the same as in 
normally fertilized beets. 

So far as my own experience goes, an excess of phosphoric acid may 
manifest itself in a shortening of the root system,— the usual result of 
culture in all highly concentrated solutions, and also in shortening the 
vegetative period with a premature ripening of the crop. The plants do not 
develop fully, the leaves turn yellow prematurely, and, accordingly, the 
yield is smaller than it would otherwise have been. 

g. Excess of Carbon Dioxid. 

Experiments on the effect of carbon dioxid content in the air and soil, 
greatly in excess of the normal, have led to contradictory results. While 
some observers have recognized only injurious effects, others report a 
satisfactory development. These apparent contradictions may be due to 
the fact that with carbon dioxid, as with all other nutritive substances, the 
effect depends upon how simultaneous the activity of all the other growth 
factors may be. The activity of the plants is generally adjusted to the 
small normal carbon dioxid content of the air-. They sometimes respond 
to a greater increase of carbon dioxid by arresting growth, sometimes by 
increasing it, depending upon whether the carbon dioxid increase occurs 
suddenly, or gradually, and whether the amount of light and warmth, water 
and nutrients permits the individual utilization of the increased amount of 
carbon dioxid. Godlewski" has substantiated this point of view by 
experiment. 

Our hot bed plants furnish abundant proof of the favorable affect. 
According to E. Demoussy's investigations*, this is due not only to an in- 
creased warmth, but actually also to an increase of the carbon dioxid in the 
air of hot beds, sometimes amounting to more than two thousandths parts. 
In comparative cultures, the air of the hot bed, which after careful testing 
showed no ammonia, had furnished nearly three times the harvested weight 
of plants grown in ordinary air under otherwise similar conditions. 

1 See lecture by H. Roemer; cit. Blatter f. Zuckerrubenbau 1905, p. 229. 

2 Brown, F., and. Escombe, F., Der Einfluss wechselnden Kohlensauregehaltes 
der Liuft auf' den photosynthetischen Prozess der Blatter und auf den Wachstums- 
modus der Pflanzen. — Farmer, J., & Chandler, S., tJber den Einfluss eines tJber- 
schusses von Kohlensaure in der Luft auf die Foiin und den inneren Bau der 
Pflanzen. Proceed. R. See. LXX. cit. Centralbl. f. Agrik.-Chemie 1903, p. 586. 

a s. Sachs, Arbeit, d. Bot. Instituts zu Wiirzburg. Part III. 

4 Compt. rend, de I'Acad. d. sciences 1904. cit. Centralbl. f. Agrik.-Chemie 
1904, Part 11, p. 745. 



407 

The fact that experiments in steriUzed soil, as contrasted with those in 
non-sterilized soil, resulted in much smaller amounts of yield, is ascribed 
by Demoussy to the killing of the micro-organisms which, by their activity, 
contribute to the decomposition of the carbon dioxid production. It is also 
probable that the growth of plants close to the ground is favored by the 
carbon dioxid constantly given off by the soil, since it has often been de- 
termined that air at the surface of the soil contains more than three ten 
thousandths carbon dioxid. 

In air in which the carbon dioxid has a tension five times above the 
normal, a great many different plants increased about possibly 60 per cent, 
more in weight than they did in ordinary air. These also blossomed earlier 
and more abundantly^. 

If plants, which naturally behave differently according to species and 
individuality, are no longer able to utilize the carbon dioxid given them, 
their life functions must cease. Kosaroff- distinguishes between a specific- 
ally injurious effect, and one due indirectly to the decrease of the partial 
pressure, or rather, the removal of oxygen. As a result of the depression 
of the transpiratory current, the plants wilt. Bohm^, like Saussure, ob- 
served that germination was retarded, in that with an increase of carbon 
dioxid, the roots and stems constantly became shorter and shorter. The 
chlorophyll formation and assimilation were considerably decreased. 

Neither can geotropism be perceived in articulated plants (Gramineae 
Commelinaceae, etc.) in a carbon dioxid atmosphere, nor may a stimulus, 
found in the air, initiate any bending*. 

Finally, when carbon dioxid begins to be excessive, the effect may first 
be beneficial, then later gradually harmful. Reference should be made 
here to the experimental results obtained by Brown and Farmer^. They 
observed that, with an increased carbon dioxid content in the air, all the 
parts containing chlorophyll became a darker green after 8 to 10 days, and 
the starch content increased, but the internodes became short and thick, 
the leaves rolled up even to the point of deformity, the flower buds dropped, 
or their primordia were not formed. 

Such conditions as are given in the experiment need scarcely ever be 
feared in practice. Such cases occur most frequently in hot beds where the 
manure, needed to raise the temperature of the beds, sets free too much 
carbon dioxid. This trouble may be overcome by proper ventilation, (even 
on frosty days.) 



1 Demoussy, E., Sur la vegetation dans des atmospheres riches en acide car- 
bonique. Compt. rend. CXXXIX, p. 883. 

2 Kosaroff, P., Die Wirkung der Kohlensaure auf den Wassertransport in 
den Pfianzen. Bot. Centralbl. 1900, Vol. 83, p. 138. 

3 Sitzungsber. d. "Wiener Acad. 1873 vom 24. Juli. 

4 Kohl, Die paratonischen Wachstumskriimmungen der Gelenkpflanzen. Bot. 
Zeit. LVIII, 1900, p. 1. 

5 Lioc. cit. 



SECTION II. 



INJURIOUS ATMOSPHERIC INFLUENCES. 



CHAPTER IV. 



TOO DRY AIR. 



Injury to Buds. 

Although in house plants, for example, we have constantly met with the 
lack of sufficient atmospheric moisture as a factor in the production of the 
phenomena of disease, it has as yet been but very little taken into 
consideration. 

The direction in which continued great scarcity of atmospheric moisture 
makes itself felt may be seen from the peculiarities of the xerophytes. As 
an example of this, we will mention Grevillius\ He found in the plants 
of a treeless lime plateau a thickening of the epidermis and its wax coating, 
or, as a substitute for this, a great increase of pubescence. These char- 
acteristics are more marked in leaves near the top of the stem. The epi- 
dermal cells, in contrast to normal forms, usually have somewhat smaller 
lumina. The palisade cells are broader and more closely joined to one 
another, the intercellular spaces are smaller; the mechanical tissues in the 
branches and petioles are better developed, the pith less ; it has smaller cells 
but is richer in starch. These changes, in fact, occur almost always in con- 
nection with a great lack of moisture in the soil whereby it is hard to judge 
which is due to the dryness of the air alone and which to the excessive 
transpiration conditioned by it. However, we find various processes setting 
in when, with a sufficient supply of soil moisture, the air is constantly hot 
and dry ; these will have to be discussed here. They are in part phenomena 
of arrestment in the life of the buds or in the conditions of germination; 
in part disturbances in the mature leaves which lead to the falling of the 
leaves in summer. 

Two stages must be noticed in the life of the buds and the development 
of the young shoot after the bud has unfolded. If a considerable dry period 



1 Grevillius, Morpholog-isch-anatomische Studien lib. d. xerophile Phanero- 
g'amen -Vegetation der Insel Oeland. Englers Jahrblicher 1897, XXIII, p. 24. 



409 




SSog 





sets in in the early spring when, as a rule, it is continued by a persistent 
East wind, the opening of the buds, dependant on the alternating action of 
sunshine and rain, will be delayed. The gummy masses 
in the bud scales of many varieties of trees, usually due 
to the gelatination of the tissue, must be softened by rain 
to facilitate the development of the buds, while the resin- 
ous and partially balsam-like products of this softening 
in the scales, warmed by the sunshine, 
give way at the same time to the pres- 
sure of the buds. In continued dry and 
windy, spring weather, the buds unfold 
more slowly because the necessary 
growth of the inner side of the scales 
is prevented so that they cannot turn 
back far enough. 

In the second kind of injury, the 
young tip of the shoot, just appearing, 
is suddenly exposed to the sharp rays 
of the sun and to very great evapora- 
tion in abnormally dry air, after the 
protecting scale has been thrown off. 
In order to understand this process, we 
give a few illustrations from Griiss^ 

In Fig. 67 is shown the cross-section ;;^^-^QC 
through the bud covering of the oak ; 
in Fig. 68, one through Pinus Mughiis. 
It is easy to distinguish the different 
scales firmly overlapping above the 
strongly developed epidermis of the 
outer side and, by comparing the 
two bud coverings, the increase of 
precautionary protection in the conifers 
is found to take place by means of the 
deposition of masses of resin (h). In 
the cross-section of the individual cov- 
ering scales it is noticed that their outer 
or, later, under side possesses especially 
strongly developed elements. In the 
pine, the epidermal cells have been very 
greatly thickened sclerenchymatically. 
The bud covering of the winter oak is 
composed of 8 separate scales, and its cell layers found underneath the epi- 
dermis are so strongly thickened that the lumina have almost disappeared. 











Fig-.67. Cross-section Fig.GS. Cross-section 
through the bud through the bud 

covering: of Quer- covering of Pinus 
cus sessili flora, Mughus, Scop. 

Sm. (After Griiss.) (After Griiss.) 



1 Griiss, J., Beitrage zur Biologic der Knospe. 
schaftliche Bot. Vol. XXIII, Part 4, p. 637. 



Pringsheims Jahrib. f. wissen- 



410 

The summer oak, Quercus pedunculata, Ehrh. behaves somewhat differently. 
If, in the Spring, a basal growth increases the sclerotic elements, the cover- 
ing scales show a certain stiffness and remain longer attached to the growing 
shoot. They thus protect it longer from the dangerous fluctuations in tem- 
perature. The oak in the warmer Mediterranean countries, Quercus Ilex, L. 
hardly shows the sclerotic elements in its scantier bud coverings, and some- 
times they are entirely lacking. In this we are concerned with protection 
against the summer drought period and find it in the hairs, which develop 
from the epidermis, and also the cork layer, which develops from the sub- 
epidermal tissue. 

Before the leaves burst out from the bud, the scales, bent together like 
a roof, are simply small leaves reduced to stipules, but when the leaves 
break out, the under side grows further at the base, while the sclerotized 
outer side does not do so. Consequently the base of the scale, drying from 
the edges backward, become fleshy, cushion-like and, like a prop, presses 
the scale outward. This is the time of danger, since even the delicate vege- 
tative cone is exposed to the fluctuations of temperature, and almost with- 
out protection. This explains the internal ruptures made by the action of 
the frost, sometimes found in the spring^ and also the phenomena of 
shrinking from drought, resulting from constant sharp East winds. 

No matter in what way the protective apparatus of the bud scale is 
formed in the various species, whether from sclerotic cell layers or from 
cork layers, layers of hair or masses of resin, the fact holds good that this 
apparatus develops differently in different years, according to the weather 
and the amount of nutriment at the time of its formation, and, accordingly, 
is of different protective power in the following spring. If, for example, 
the summer has been moist and cloudy, the covering scales tend to develop- 
ment towards the nature of the green leaf and the cells become larger or 
less thickened. In spring they react more quickly to the increase of turgor 
of the tissue and separate from one another more quickly. Thus the grow- 
ing point is exposed prematurely to inclement spring weather, and so loses 
too rapidly the protection against its power of transpiration. 

This factor must not be underestimated, for Griiss reports- that, 
when he removed the strongly developed outer scales from an oak 
bud, he noticed that the bud was destroyed with great regularity, even 
if the temperature did not fall and there was present sufficient moisture. 
Also the inner, more dehcately walled coverings became dry since they were 
not accustomed to the increased transpiration. Uninjured buds kept under 
similar conditions (on cut twigs) developed further. 

Experiments with beech buds, from which the whole covering had 
been removed, showed that the young, exposed leaves kept fresh much 
longer than those of the oak. This is due to the pubescence of the young 
beech leaves, which protect them from too great transpiration and the con- 



1 See chapter on the Action of Frost. 

2 Loc. cit. p. 649. 



411 

sequent drying. This view is supported also by the observation of Griiss, 
that, in Aesculus Hippocastanum, the young leaves, known to be very 
thickly pubescent, will develop normally after the removal of the bud cover- 
ing. The effectiveness of the resin covering is seen from an example of 
Abies Pinsapo, Boiss. When the resin had been removed from the buds 
by carbon disulphid, they dried up. 

It may now be asked how such irregularities in the unfolding of the 
buds can be combatted practically. 

The formation of the bud covering cannot be influenced and the danger- 
ous fluctuations in temperature and atmospheric moisture in spring cannot 
be controlled. Nevertheless, we think a precautionary measure might in- 
deed be adopted in forestration in order to moderate the extremes of trans- 
piration. In the first place, the soil should retain its natural covering of 
moss or litter, since in this way the soil moisture is preserved, and a damp 
atmosphere made possible. Hence it might be advisable not to clear away 
all the leaves, etc. Finally, however, and especially in younger plantations, 
it might be advantageous to retain protective forests on the side of the tract 
exposed to the strong spring sun. Among such protective trees the rapid 
and loosely growing birch is especially useful. 

In garden plants, naturally, one can control conditions very much 
better. In this conne^ction, attention should be called for the present only 
to the fact that one should not attempt to replace the uniformly great loss 
from transpiration by increasing the water at the roots. That does not work 
well and plants are found to dry up which have an excess of water at the 
roots. The only natural means is artificial shading. 

Defoliation Due to Heat. 

Observation shows that every year from spring on the foliage falls 
from our deciduous trees. In city planting this is especially noticable in 
Acer Negundo and the slightly developed inflorescences of the linden show 
this almost at once, sometime before the "linden blooms." The process is 
less striking, but constantly present in other deciduous varieties. Wiesner^ 
gives this constant dropping of separate yellow leaves the special name of 
"the summer defoliation" and sees its cause in the changes in the sun's 
altitude. I think that other causes can also operate here, for, while the 
summer defoliation usually sets in predominately after the 21st of June, 
observations show that, for example, according to Wiesner's statements, in 
Acer Negundo, Acer Calif ornicum., and related species, the leaves first 
formed may be dropped even in May and at the beginning of June. 

As long as this loss of leaves is slight in comparison with the whole 
foliage of the tree, it has no pathological significance. Experiments have 
shown that it is a perfectly normal phenomenon for the leaves on a branch 
to complete their cycle of growth at different periods. Thus some would 



1 Wiesner, Jul., tJber Laubfall infolge Sinkens des absoluten Lichtgenusses 
(Sommerlaubfall). Ber. d. D. Bot. Ges. 1904, p. 64. 



412 

fall earlier, some later. Those produced first in the spring are weak in 
their formation, being smaller and not so brightly colored; hence they soon 
reach their full development, Avhen their assimilation is arrested, as the 
stronger leaves, produced later, cut off their light. Then the tree frees itself 
of the organs incapable of working. 

However, the summer defoliation is to be considered as a phenomenon 
of disease when it becomes extensive and suddenly attacks the well develop- 
ed foliage in full sunhght. Late frosts and more often a continued period 
of drought, combined with great heat, are among the causes of summer 
defoliation. Wiesner distinguishes the latter form as "defoliation due to 
heat," clearly a result primarily of excessive transpiration with an unequal 
decrease in the supply of water in the trunk. 

I found examples of defoliation due to heat in the trees planted along 
the streets, especially among the lindens, in spite of abundant watering. 
From this it is evident that actually the dry air with abundant sunshine 
should be assumed to be the injurious factor. With deficient water supply 
in the soil alone the foliage dies from summer blight but usually remains 
hanging on the tree. 

The linden, despite its beauty, is not to be recommended as a street 
tree because of its especial sensitiveness. The summer linden shows earlier 
and more severe effects than the winter linden, and after the appearance of 
summer heat, almost without exception, is found covered with the fine webs 
of the weaving mite {Tetranychus telarius). In many trees aphids occur 
in immense quantities. After defoliation, from which only the tips of the 
branches are excepted, there is manifest a prematurely dormant period. As 
soon as the weather becomes cooler (or when the streets are abundantly 
watered during the hot period) a second growth appears in which the de- 
velopment of lateral buds can push off the hanging leaves (defoliation due 
to growth, according to Wiesner). In wet autumns the wood of this second 
growth does not ripen properly and is easily injured by the winter frosts. 

In order to avoid these conditions it is advisable to plant elms rather 
than lindens along the streets. If these conditions appear along avenues of 
older trees, v/hich cannot be replanted, the streets must be sprinkled as 
frequently as possible. Spraying under heavy pressure in the late evening 
may prove to be especially useful. I consider that consistently following 
this measure will prove the most effective prevention of vermin attacks. 

Honey Dew. 

According to observations made up to the present, a disease must be in- 
cluded here which has often^ been described under the name "honey dezi'" 
{Melligo, Melaeris, Ros mellis) and which has been traced to very different 
causes. This disease is characterized by the appearance of a sugary coating 

1 Saccharogenesis diabetica; Unger. "Exanth. p. 3.— Honning- Dugen, Fabricius 
Kiobenh. 1774. — Le Givre, Adans, cit. bei Seetzen: Sistematarum generaliorum de 
morbis plantarum. Gottingae 1789. 



413 

on leaves, blossoms and young twigs of woody and herbaceous plants usually 
covering the outer surface of the organs, sometimes as a shining uniform 
varnish, sometimes in the form of yellowish tough drops. Meyen^ relates 
that for some time tlie theory expressed by Pliny was accepted, namely, 
that the honey dew was an actual falling from the air, occurring in the dog 
days especially and coating not only the plants, but even the clothing of 
men. T- Bauhin contradicts this theory and calls attention to the fact 
that only isolated plants or species in any region become diseased. After 
the excretion of a sweet sap from the anus or the abdominal tubes of the 
aphids had been observed, they were considered to be the cause of the dis- 
ease and at the time it was observed that aphids and honey dew were fre- 
quently found together. To this, however, was opposed first of all, the fact 
that the aphids usually occur on the under side of the leaf, the honey dew, 
chiefly on the upper side. However, this fact is no very certain proof 
since the aphids of the under side of the leaf can sprinkle the upper side of 
the leaf lying next below. But gradually the observations on honey dew- 
were increased on isolated outdoor and indoor plants on which no aphids 
could be found or upon which they did not appear until sometime later. 
Hartig's observation, made in 1834, is interesting in this connection. A 
rose plant, wdiich had not been taken from the house, secreted small drops 
on the under epidermis of the leaves from which the sugar was separated 
in rhomboidal or cubical crystals. Tn this the green color of the leaves 
changed to a grayish one, due to the disappearance of the chlorophyll in 
the mesophvll at the secreting places and to the appearance of clear drops 
in the cells. Treviranus", in the same way, frequently found such sugary 
secretions in the warm, continuously dry air out of doors as well as in 
greenhouses, on white poplars, lindens, orange trees, distils (Carduus 
arctioides) and cited still older observations by Lobel, Pena, Tournefort et 
al., according to wdiich honey dew occurs on olive trees, varieties of maple, 
walnuts, willows, elms and spruces. He, and later Meyen, were convinced 
that the drops containing sugar were secreted directly from the epidermal 
cells, to which the former observers also added that the stomata did not 
take part in this secretion. Further observations on honey dew occurring 
in very different plants, especially oaks, were furnished later by Gasparrini''. 
The honey dew on the linden has been chemically investigated by 
Boussingault and that on the grape cherry (Prunus Padus) by Zoller^ 
Boussingault found that the honey dew% collected at two different times, 
differed quantitatively in regard to the different substances; from which 
fact it is evident, that the secretion does not always have the same per- 
centage composition. But the nature of the substance seems to change also, 
for although Boussnigault found only cane sugar (48 to 55 per cent.), in- 
vert sugar (28 to 24 per cent.), and dextrin (22 to 19 per cent.), Langlois 

1 Pflanzenpatholoj?ie, 1841, p. 217. 

2 Phvsiologie der Gewilchse, 1838, Vol. II, Part I, p. 35-37. 

■" Sopra la melata o trasudamento di aspetto goommoso etc. Bot. Zeit. 1864, 
p. 324. 

* Okonom. Fortschr. 1872, No. 2, p. 39. 



414 

also found mannit as one constitutent of the honey dew on the linden. 
Czapek^ collected the results of more recent observations. From this it 
may be concluded that the composition of the honey dew varies in different 
plants. 

A harmony of the theories as to the causes of the phenomenon has not 
been obtained as yet. While Biisg'en- studied carefully the aphid stings on 
plants, he proved that the animals secrete through the anus much larger 
amounts of honey dew (the secretions of the abdominal tubes are waxy) 
than is usually assumed, and, on this account, he concludes that real honey 
dew depends only on aphids. Bonnier^ made some experiments which showed 
an artificial production of honey dew without the intervention of the 
animals. 

Biisgen says the peculiarities of the cuticle allow neither an osmosis 
or distillation of sugar saps from the interior of the cell nor, as Wilson 
assumed, an osmotic withdrawal of liquids through drops of sugar to be 
found on the surface of the leaf, such as are formed by the excretion of 
the aphids. This statement, however, does not consider the fact that the 
smooth surface of the cuticle can become broken and that secretions in 
individual cases can find their Avay through the stomata. Bonnier's results 
prove the later case. Leaves which had been exposed to great differences 
in temperature (conifers, oaks, maples, etc.), showed under the microscope, 
when examined by direct illumination, the formation of nectar-like drops 
from the stomata when the light was sufficiently strong. 

My own observations confirm the occurrence of honey dew without the 
intervention of aphids. In one case T found an abundant formation of honey 
dew on the older leaves of pear seedlings grown in water cultures and 
exposed to the hot July sun. This observation showed that deficient soil 
water was not necessarily a factor. I believe that honey dew is produced 
if there is a sudden excessive increase of transpiration in strongly function- 
ing active leaves, caused by a strong light stimulus, and brings about too 
high a concentration of the cell sap. If the disturbance continues beyond 
a certain point, the leaf suffers permanently and falls prematurely. In 
another case the rain gradually washed the sugar coating away, which made 
possible an attack of the black fungi (sooty dew). The production of 
honey dew is not always dependent upon extreme and absolutely high 
temperatures and strong light stimuli, but sudden great contrasts as, 
for example, the sudden shock to an organism caused by an intense morning 
sun following a very cool night, which had suppressed its activity. 

Shading would be the best preventative measure and repeated 
sprinkling an effective remedy. 



1 Czapek, Fr., Blochemie der Pflanzen. Jena. Gustav Fischer. 1905, Vol. I, 
p. 408. 

2 Biisgen, M., Der Honigtau. Biolog. Studien an Pflanzen u. Pflanzenlau.sen. 
Sond. Biologisches Centralbl. Vol. XI, Nos. 7 and 8, 1891. 

3 Bonnier, G., Sur la miellee des feuilles. Compt. rend. 1896, p. 335, cit. Zeit- 
RChrift f. Pflanzenkrankh. 1896, p. 347. 



415 

Probably the much dread Mafuta disease of the sorghum millet 
(Andropogon sorghum) in German East Africa belongs here. The word 
Mafuta means oil. Honey-like excretions are found on leaves and stems. 
These give rise to a sooty coating'' . Other plants also suffer especially in 
times of drought. 

Heart Rot and Dry Rot of Fodder and Sugar Beets^. 

The heart rot of the sugar beet should be considered as a phenomenon 
usually related to honey dew^. It is found usually in hot Julys in rainless 
periods and is characterized by the death of the heart leaves. These have not 
grown to half their normal size. The dying foliage suddenly becomes black. 
In severe attacks the whole leaf area dies, but, as a rule, the plants develop 
new foliage. In addition to the affection of the leaves, the body of the 
beet is attacked by a decomposition or dry rot. The beet, near its head end, 
has spots which can deepen as the tissues decompose, and finally destroy the 
beet. Of greater agricultural significance in this connection is the fact that 
a part of the non-reducing sugar disappears from the beet and another part 
is converted into reducing (grape) sugar". If the rainy weather sets in at 
the right time, the dead tissue can be thrown off through the formation of 
cork. 

If the healing process does not set in soon enough, so that a long con- 
tinued autumnal dampness can exercise its influence on the decayed places, 
the process of destruction of the beets, which are poorer in sugar, is also 
continued in the storage pits. 

Most observers are inclined to seek the cause of the trouble in fungi, 
since mycelium is often found in the diseased heart leaves*. Frank 
especially defended the fungi theory and wished to make two species re- 
sponsible for it : Phoma Betae, Frank^ and Fusarium heticola, Frank. 
It is certain, however, that the first stages of the disease of the heart leaves 
are without fungi and bacteria, and the parasites later, during damp weather, 
occasion an advance in the destruction of the tissue. However, when the 
beet plants are healthy, the fungi cannot attack them. Only when evapora- 
tion is sufficiently increased and the absorption of water sufficiently de- 
creased do the conditions arise which predispose the plants to attack by 
fungi. 

Practical workers state that the addition of lime also in the form of 
waste lime favors the attack of the disease. We have very instructive 
field experiments^ along these lines in which some areas were limed, and 
some not. Where lime was used, the beets were diseased, where there was 
none, the crop was healthy. 

1 Busse, W., Weitere Untersuchungen liber die Mafuta-Krankheit der Sorghum- 
Hirse. Aus "Tropenpflanzer," cit. Zeitschr. f. Pflanzenkrankh. 1902, p. 82. 

2 See Vol. II, p. 240. 

3 Frank, A. B., Kampfbuch. 1897, p. 131. 

4 Prillieux et Delacroix, Complement a I'etude de la maladie du coeur de la 
Betterave. Bull. Soc. mycologique. VII, 1891, p. 23. 

5 syn. Phoma sphaerosperma, Rostr., Phoma Betae, Rostr., Phyllosticta tabifica, 
Prill, et Del. 

6 Zeitschr. f. Pflanzenkrankh. 1895, p. 250, 1896, p. 339. 



4i6 

Also the location itself has often been found to favor the appearance 
of the disease, since on field ridges with a gravelly underground, or declivi- 
ties from v\^hich the water runs away quickly, often only dry rotted beets 
are produced. The different varieties are proved to be susceptible to 
different degrees ; the Vilmorin sugar beet is said to be especially sus- 
ceptible ; varieties with smooth leaves spread flat on the ground and long 
roots should be preferred in threatened regions^. 

Sasse-, as a result of his very thorough field experiments, states that 
vapor and deep cultivation prevent the outbreak of dry rot. Opinions vary 
greatly as to the influence of fertilization. In my opinion, the variation is 
explained by the varying action of the same fertilizer on different fields, 
and dependent on the weather. Fertilizers making the soils more porous, 
increasing their capacity for warmth and decreasing their power for re- 
taining water, tend to favor the development of dry rot ; this can occur with 
waste lime^. The same fertilizers are satisfactory^ in heavy soils. Fertiliza- 
tion with kainit has been most questioned. Tt is erbphasized that the soil 
will actually retain water better after fertilization with commercial manures, 
i. e. offer greater resistance to the influence of drought, and yet not infre- 
quently where kainit fertilization has been used, the first heart rot of the 
beets will be found. 

In my opinion there is a natural explanation for this phenomenon. 
Kainit tends to develop leaves extraordinarily ; hence, with a continued dry 
period, the extensive leaf area withdraws water very quickly from the root 
system, causing an injurious concentration of the cell sap. Analyses have 
shown that, with a high potassium content in the leaves, the dry rot appeared 
more marked, the smaller the proportion of phosphoric acid present. 

Therefore, the choice of land which dries quickly may be a preventa- 
tive measure for this disease. When the soil is light those materials, which 
heat the soil (lime, separator ooze) must not be given directly to the beets. 
With the appearance of dangerous droughts, one should decrease the drain- 
age since, ordinarily, it would not be practical to always water the crop. 
A further condition should be considered, namely, whether the evaporation 
of the plants can be reduced by removing the older leaves, or by shading 
with straw mulching. 

Faulty Development of the Blossoms. 

Much oftener than is generally supposed, great atmospheric dryness 
manifests itself in blossoms, especially double flowers. If specimens of the 
same species with single and with double blossoms in the same position be 
compared (fuchsias, petunias, tuberous begonias, roses, etc.), it will be 
observed without exception that the single blossoms develop more rapidly 



1 Bartos, W., Einige Beobachtung^en iiber die Herz- unci Trockenfaule, cit. 
Centralbl. f. Bakteriologie 1899, p. 562. 

2 Sasse, Otto, Einig-e Beobachtungen aus dem praktischen Betriebe betreffs 
Auftretens der Herz- oder Trockenfaule. Zeitschr. f. Pflanzenkrankh. 1894, p. 3.59. 

3 Richter, W., tjber die Beziehungen des Scheideschlamms zum Auftreten der 
Herzfaule der Riiben. Zeitschr. f. Pflanzenkrankh. 1895, p. 51. 



417 

and quickly. The slower and more retarded dexelopment of double blooms 
may be traced to greater distribution of the water and nutritive substances 
conveyed through the petioles over a more considerable leaf area. The loss 
in transpiration, due to the increased number of petals, is greater and can 
in no way be replaced by supplying w ater to the roots. Consequently, the 
organs develop more quickly ; they become ripe prematurely and cease 
growing before the blossom has been completely developed. On this account 
half open blossoms often fall where there is great atmospheric dryness. 
This should not be confused with the dropping of the blossoms, due to 
excess of water. In the latter case it may often be observed that both the 
blossoms and peduncles fall. \\^ith excessive transpiration in a very dry 
atmosphere, the petals fall where they join the peduncle after having 
turned brown there. 

AMien, as is often attempted in greenhouses, an artificially moist atmos- 
phere is produced by abundant watering of entire plants, their condition is 
improved only if the flower pots stand on the soil, since the vaporizing 
dampness from the soil keeps the atmosphere constantly moist. But if the 
pots stand on wood, iron or stone, the blossoms shrivel up in spite of the 
watering and a Botrytis growth is found where the petals loosen. This 
leads consequently to erroneous conclusions since Botrytis diseases are 
usually accompanied by great atmospheric humidity. 

The double staminate blossoms of tuberous begonias fall in excessively 
dry air, and form one of the most striking examples of the difficulty. I 
observed this often in the dry summer of 1904 in places which had never 
had direct sunlight. That the falling of the petals was actually due to dry- 
ness of the air was shown l)y an experiment in which plants were used, 
which usually drop their blossoms at the time of opening. They retained 
and developed them, however, if placed over broad basins filled with water. 

The pistillate blooms always mature. The first indication that the 
staminate blossoms are going to fall is that the bud does not straighten up 
but remains drooping. AA'ith the hand lens a small brown ring may be seen 
at the union of the calyx and peduncle. There the young tissue is found 
to be deep brown, its walls and contents collapsed. At the calyx, the 
shrivelling and tearing of the tissue forms large holes until finally the petals 
hang only by a few shreds of tissue. In the individual petals, the vascular 
bundles also seem deeply browned even at the places which are still not 
discolored and apparently fresh. This drying of the base is really a pre- 
mature end of the life cycle, since the cell contains only scanty flakes of 
protoplasm. Near the dead tissue there is an abnormal accumulation of 
asymmetrically formed, separate crystals of calcium oxalate, as the final 
residue of the organic substances consumed in respiration. 

A second kind of defective blossom development, resulting from dry- 
ness, was observed in the Liliaceae and Amaryllideae. In these instances 
the perianth remained stuck together at the apices. Although the rest of the 
blossom was normally developed and colored, the tips of these perianths 



4i8 



turned yellow, sliivelled up and dried into a mass which finally crumbled. 
The injury is horticulturally of significance only when the blooms are forced 
and large individual blossoms are desired as in Lilium aureum, Liliuni longi- 
florum and Hippeastrum robustum, Dietr., etc. 

In that species which is known among gardners as Amaryllis Tettaui 
and is often grown as a house plant because it blooms freely, I observed 
more carefully the mechanics of opening and incomplete development dur- 
ing drought. 

The three outer tips of the brick red perianth begin to separate from 
one another at their base on the day before the blossoms are completely 
opened; hence the large conical flower bud first of all shows three shts. 

The tips of these three outer- 
most petals, however, remain 
stuck fast together even if 
the process of separation from 
one another is so hastened by 
the increased growth of the 
innerside of the perianth that 
this is curved outward like a 
pouch. In this convexity, 
which becomes constantly 
greater, lies a great elasticity 
which would be able to sep- 
arate the gummed tips from 
one another and, in normal 
cases, actually does tear them 
apart. The strength of this 
elastic power, produced by 
the basal epinasty of the 
perianth, is demonstrated if 
the still gummed apices of the 
three tips are cut off about 
forty-eight hours before the 
normal time of opening. Then, within lo minutes, the individual tips have 
separated 1.5 to 2 cm. from one another, i. e. the corolla has begun to open. 
The resistance offered to this strong elasticity arises from the fact that the 
green apices of the three outermost tips are anchored to a strong cone about 
5 cm. long. Sometimes this cone is thimble shaped. There is a heavy 
growth on the underside of each tip which curves out like a ridge, and 
corresponds with a midrib, making a very fleshy growth on each tip. 

Fig. 69 shows three of the perianth tips, touching each other with their 
keel-like wedges (a). These wedges contain no vascular bundles. These 
lie {g) frequently in groups of 3 or 4 peripherally in the real laminal part. 
The individual laminal halves at both sides of the fleshy median ridges are 
curv^ed inward and touch the adjacent peripheral tip with their edges (r) ; 




U...4^- 



a 



Fig-. 69. Cross-section throug-h the apical region 

of a still closed blossom of Hippeastrum 

robustum. Explanation of the letters 

in the text. 



419 

these are green, while the fleshy cushions at the center (c) , containing the 
largest parenchyma cells, seem colorless. In contrast to the abundant small 
grained masses of starch in the rest of the tissue, the cushions display only 
a few large starch grains. The epidermis is normally flat walled at the 
outside of the peripheral tip, but, on the ventral side, at the beginning of 
the development of red coloring matter, shows a papillary outgrowth. Al- 
though this grew out to distinct pajjillae, mutually interlocking, like 
clogged wheels, on the cushion-like raised places (a), it shows scarcely 
any elongation on the flat laminal part. 

In this close interlocking of the papillae of the tip of one part of the 
perianth with those of the others may be seen the reason for anchoring 
these tips so firmly together. An elastic strain loosens the tips since these 
pai)illae grow rapidly to conical hairs, thus breaking the connection. In 
the cavities (h) which the outer petals leave free, lie the tips of the three 
inner ones, whose epidermis, however, develops papillae sooner than that 
of the outer ones. The mutual resistance of the out-growing papillae 
favors the separation of the inner tips of the perianth and, therefore, the 
blossoming. 

When the atmsophere is dry, the primordia of the papillae may still be 
found, but they do not develop into conical hairs ; hence the tips of the 
petals remain united and gradually shrivel up. 

House Plants. 

The typical picture of a house plant which meets our eye shows brown- 
ing and drying leaf tips. Where gas is burned, usually one is inclined to 
lay the blame on the gas. As a fact, the dryness of the air in the room is 
the cause and the condition is as marked in dwellings where gas is not used. 
The fact that plants, especially the so-called foliage plants, die after the 
tips become brown and dry, may be explained as due, not to the atmos- 
pheric dryness, but to the attempts of the grower to get greater moisture in 
the air by very frequent watering. However, the plants get no benefit from 
this increased supply of water. They can use more water and transpire 
it only when the tissue develops more abundantly, resulting in a more 
vigorous assimilation and a greater production of leaves. The dryness of 
the air, however, inhibits this very development of the leaves. 

When the foliage of tropical climates (many foliage Begonias, Hoflf- 
mannias, RuelHas, Marantes, etc.), are brought from the moist conservatory 
into a room of the same temperature, the development at once ceases. The 
older leaves begin to curl back; the younger ones roll up their edges and 
remain smaller than those previously formed. The apical growth of the 
shoots is retarded ; all processes of elongation are reduced. It is peculiar 
that with many plants (for example, many bushy Begonias) the blossoms, 
produced in dry air, either do not open at all or only incompletely, and 
finally fall off without having become diseased. This process may also be 
observed out of doors. The dormant period of the plant sets in more 



4'20 

quickly, and, when tlie new vegetative period begins, the development of 
the buds is retarded and often entirely prevented. With such activity in 
the parts above ground, the roots will rot if given too abundant water. 

Various methods have been proposed to overcome the injurious in- 
fluence of the dry air in the room, such as to spray frequently or to cover 
the plants at night with damp cheese cloth, etc. However, such methods 
have not proved sufficiently satisfactory. I obtained best results by using 
Wardian cases or by setting the plants over water. Recently flower tables 
have been used in which the plant stands on a zinc box filled with water, 
the top of which has been punctured full of holes. Through this, water 
vapor constantly rises between plants placed above it. 

Hard Seeds in the Leguminaceae. 

The hard-shelled condition of Leguminaceae seeds, not only those of 
the Papilionaceae, but also those of the Mimoseae and Caesalpiniaceae, can 
be considered as a natural protection against micro-organisms at a time in 
their development when they are most readily infested. All our wild grow- 
ing Papilionaceae exhibit the same constructive principle and the hard- 
seeded condition becomes dangerous only when it prevents germination. 

This hard-shelled condition arises from the special thickening of the 
palisade layer of the seed grain which, with its cuticle, forms the outer- 
most covering of the seed shell. These columnar palisade cells, lying very 
close to one another, show in cross-section strongly refractive cross lines 
(light lines) of an especially dense substance. The cell content contains 
those substances which cause the coloring of the seed shell and to which 
great importance is ascribed as substances protective against parasite at- 
tacks. Next to the palisade layer, described by Nobbe as the "hard layer," 
lies, on the under side, a layer of so-called hour-glass cells, next which are 
thin-walled cell layers with large intercellular spaces. These cells function 
especially in the swelling of seed. Corresponding to the gluten layer in 
grain seeds, we find in the majority of Leguminaceae seed, with the ex- 
ception of the Phaseoleae. Vicieae and a few other varieties, according to 
Harz\. the endosperm in the form of a hard, horny matter, which becomes 
slimy when placed in water. In the region of the scar, palisade cells and 
round hour-glass cells usually appear in two rows. 

In this instance we follow Hiltner's experiments-, which show that the 
hard-seeded condition preventing the rapid swelling of the seeds, naturally 
forms a protection against micro-organisms. Older lupine seeds, wdiich 
were not absolutely hard-shelled but swell up only wdth difficulty, were 
soaked in water. The seeds which swelled each day were laid separately 
in the germinating box. This showed that those lupine seeds which swelled 
most rapidly and hence w^ere not hard-shelled; almost always rotted, while 



1 Landwirtschaftliche Samenkunde. 

- Hiltner, I^., Die Keimungsverhaltnisse der Leguminosensamen und ihre 
Beeinflussung durch Organismenwirkung. Arbeiten d. Biolog. Abteil. f. Land- u. 
Forstwirtsch. am Kaiserl. Gesundheitsamte. Vol. Ill, Part 1. Berlin 1902. 



421 

the percentage of g-ermination was higher in those seeds where the swell- 
ing hegan later; due to the higher percentage of hard seeds. 

It was concluded from experiments with eight year old clo\er seed 
which, on account of age, had already begun to grow dark, certain seeds 
having become brown and shrivelled, and which was sorted according 
to color, that the grains, which still had the appearance of completely fresh 
seed, gave the highest percentage of germination. Among the slightly dis- 
colored seeds, the brown ones germinated least and gave more than 90 per 
cent, of rotted grains. Among these seeds, a much larger percentage of the 
light-colored ones decayed than of tlie violet ones. This led to the deduction 
that the violet color of the seed covering offered a protection against bac- 
terial attack. 

The different percentages of hard-shelled seeds from a given variety 
over a period of several years, show the dependence of that condition on 
the weather. Hiltner, by drying the seed artificially at a temperature of 
35°C., or over sulfuric acid, could increase the percentage of hard-shelled 
grain. This experiment showed the atmospheric condition required to pro- 
duce the undesired hard-shelled seeds. This condition, therefore, resembles 
glassiness of grain. As the process of drying during ripening is hastened, 
more hard-shelled seeds might be formed. 

In general practice, however, contradictory results are often found. 
In dry positions it was observed that the seeds of lupines, vetches, scarlet 
clover and the kidney vetch (anthyllis ) (W'indklee), in time become hard- 
shelled, while the finer clover seeds show rather the reverse. Hiltner's 
observation on artificially dried seeds explains this contradiction. The in- 
fluence producing an increased toughness of the shell in thick-walled seed 
aff"ects thin-walled seeds as well, but in them the shell splits, consequently 
increasing their small capacity for swelling; further Rodewald states that 
cold can decrease the hard-shelled condition of Leguminaceae seeds, 

\\'hen one realizes that hard seeds can lie for years in the soil without 
germinating and that those, even less capable of swelling, may germinate 
so late that they cause a second growth, it will be evident that the seed 
grower must control the formation of hard shells to eliminate them. In 
the course of years, many methods have been recommended. Thus, for 
example, the seed should be laid in a i to 2 per cent, solution of sodium 
carbonate, to dissolve the silicic acid in the shell. Again, simply sift out 
the hard-shelled seeds, since they are all somewhat smaller than the normal 
ones which will germinate. Again, treating the seeds with hot water has 
sometimes been successful, sometimes not. Dipping in boiling water for 
one minute was injurious, but was beneficial when the seed was emersed for 
five seconds only. This treatment, however, over so short a time, cannot 
be entrusted to laborers. Potassium permanganate, dilute sulfuric acid, an 
ammoniacal solution of copper sulfate, have been as unsuccessful as the 
sodium solutions. On the other hand, Hiltner found concentrated sulfuric 
acid to be successful. The sulfuric acid injured only tliose seeds which 



422 

had been damaged in threshing, even if the seed was left for sometime in 
the acid. Frequently, treatment with sulfuric acid for half an hour will be 
sufficient if the seeds have been thoroughly wet by stirring. When the 
treatment is completed the acid should be thoroughly washed ofif with clean 
water and then immediately with lime water for at least 5 to 20 minutes. 
Microscopic investigations of seed treated in this way showed that (in 
Acacia Lophanta) the sulfuric acid had removed not only the cuticle but 
also the greater part of the palisade cells and had stopped before reaching 
the "light line." Yet the seeds could swell in water only when the acid had 
penetrated the light line in some places^ Therefore, this cell layer, present 
in the seed shell of all the Leguminaceae, according to Mattirolo^, con- 
sisting of an especially dense cellulose, prevents the seeds from rapid ab- 
sorption and elimination of water. 

Connected with this innate hard-seeded condition is the hardening of the 
seed membrane during germination. With those seeds which, in germi- 
nation, pushed their cotyledons above the soil, the cap-like seed shell is 
gradually pushed off, if it has been retained until the moisture is absorbed 
and thus remains flexible. But if a hot, rainless period sets in suddenly, 
the cap dries on the cotyledons, preventing their development, as well as the 
breaking of the young stem. In case it is not destroyed, it is twisted to 
one side. Lopriore^ mentions here the germination of beans. I have ob- 
served similar phenomena in cucumbers, pumpkins, melons and the seeds of 
stone fruits. The retention of the dry, stony shell shows itself most de- 
structively in the seedlings of plums, peaches and other Amygdalaceae. 
Sprinkling of the seed bed in the evening is, therefore, a precaution which 
should not be omitted. 



1 Hiltner und Kinzel, tJber die Ursachen und die Beseitigung' der Keimungs- 
hemmungen bei verschiedenen praktisch wichtigeren Samenarten. Naturwissensch. 
Zeitschr. f. Land- u. Forstwirtschaft 1906, p. 199. 

2 La linea lucida nelle cellule malpighiane degli integumenti seminale. Torino 
1885, cit. von Hiltner und Kinzel. 

3 Berichte d. Deutch. Bot. Ges. 1904, Part 5, p. 307. 



CHAPTER V. 



EXCESSIVE HUMIDITY. 



The Mode of Growth With Continued Atmospheric Humidity. 

Older works have called attention to the fact that the structure and 
functions of individuals are altered by the influence of a high degree of 
atmospheric humidity in the same way as by the removal of light. Accord- 
ing to experiments of Vesque and Viet\ plants grown in moist air have 
longer, less branched roots, more delicate stems, leaves with longer petioles 
and smaller blades. The walls of the epidermal cells are less wavy; the 
cell rows of the mesophyll somewhat less numerous and without differ- 
entiation into palisade parenchyma. The whole tissue of the leaf grown 
in moist air is in every respect more uniform, while in dry air the difference 
between palisade and spongy parenchyma is clearly seen. The vascular 
bundles in the internodes are much more developed in dry air. This refers 
not only to the diameter of the whole bundle, to the number of ducts and 
their diameter, but especially to the hard bast fibres which may occur 
abundantly in dry air and be entirely lacking in moist air. Duval-Jouve- 
observed with grasses that dry, hot situations increased the development of 
the bast bundles, while, in moist places, this development is retarded. The 
authors named quote Rauwenhoff^ who describes etiolated plants in this 
way. In comparative experiments with dry and moist air, under light bell- 
glasses, as well as shaded ones, it was found that, in darkness but in dry 
air, the plants were less spindling than those grown in the light in moist air, 
from which it is concluded that the form of the etiolated plants is due chiefly 
to deficient transpiration. 

Brenner* expresses the same theory. In his experiments with Cras- 
sulae, he observed a tendency to decrease the succulency of the leaves in 
moist air, but to increase the upper surface. The cells of the stems were 
actually elongated. Wiesner^ also found that the leaves of Sempervivum 

1 Vesque et Viet. Influence du Milieu sur les vegetaux. Annales des scienc. 
nat. Sixieme serie. Botanique t. XII, 1881, p. 167. 

2 Botan. Jahresbericht 1875, p. 432. 

3 Annal. d. scienc. nat. 6 ser. V, p. 267. 

4 Brenner, W., U.ntersuchungen an einigen Fettpflanzen. Just's Bot. Jahresb. 
1900, p. 306. ' ^ , ^ 

5 Wiesner, Jul., Formveranderungen von Pflanzen bei Kultur in absolut 
feuchten Raumen. Ber. d. Deutsch. Bot. Ges. 1891, p. 46. 



424 

tcctorum considerably enlarged in an absolutely moist room and became 
markedly epinastic. The leaf rosettes were spread out because the inter- 
nodes developed further. W. Wollny^ found that a lessened thorn de- 
velopment occurs in normal leaves of Ulcx enropaeus as a result of con- 
tinued atmospheric humidity. He also observed, however, that the chloro- 
phyll content decreased as the leaves increased. According to Eberhardf', 
the number of chlorophyll grains is decreased if the stems become longer 
and the leaves larger. In a later work" this investigator summarizes his 
experiments as follows ; moist air combines a reduction in the thickness 
of leaves and stems with elongation. The formation of hairs is decreased, 
that of blossoms and fruit retarded. Epidermal, bark and pith cells become 
longer, the intercellular spaces greater, the number of secretion canals 
smaller and the development of the wood less noticeable. A smaller pro- 
duction of lateral roots is noticed. 

E. Wollny* also mentions that the time of blossoming and ripening is 
retarded and, by numerous experiments, strengthens the easily foreseen 
conclusion, viz., that the evaporation from plants and soil, under otherwise 
equal circumstances, is smaller, the greater the atmospheric humidity. It 
should be mentioned briefly in passing that in numerous cases abundant 
excretion of water takes place in the form of drops with the reduction of 
transpiration and by means of different devices in the various plants"'. We 
frequently find this in potted plants which in the fall are brought into un- 
heated greenhouses, when the leaves touch the rapidly cooling window- 
panes. 

Finally, I will mention the results of my own experiments''. 

In trees (pear) the whole new growth and also the different individual 
internodes and petioles were observed to be shorter in dry air, and the leaf 
blades more slender in moist air. In grains, the growth from seed was 
found to be somewhat less in dry air; the leaf number was also somewhat 
decreased, but the size of the individual leaves was increased longitudinally, 
while somewhat lessened in width. The same change in dimensions was 
also exhibited by the individual leaf cells. The influence of moist air 
elongated the leaf sheaths and also the individual blades, as well as the 
roots themselves, although the plants, even those exposed to dry air, stood 
in a nutrient solution. 

The fact that the substance as well as the form of the plants will be 
changed with varying humidity is to be surmised as a matter of course. 
In fact, my experiments show that in moist air a lesser amount of green 



1 Wollny, W., Untersuchungen liber den Einfluss der Luftfeuchtigkeit auf das 
Wachstum der Pflanzen. Inaugural-Dissertation. Halle 1898. 

2 Eberhardt, M., Action de I'air sec et de I'air humide sur les vegetaux. Compt. 
rend. 1900, t. 131, p. 114. 

3 cit. Centralbl. f. Agrik.-Chem. 1904, Part 8. 

4 Wollny, E., Untersuchungen tiber die Verdunstung und das Produktions- 
vermogen der Kulturpflanzen bei verschiedenem Feuchtigkeitsgehalt der Luft. 
Forsch. auf d. Geb. d. Agrikulturphysik Vol. XX, 1898, Part 5. 

5 s. Dot. Jahresber. 25. Jahrg., Teil I, p. 76. Abh. von Nestler und Goebel. 
G Sorauer, Studien iiber Verdunstung. Forsch. auf d. Geb. d. Agrikulturphysik, 

Vol. III. Part 4-5, p. 55 ff. 



425 

matter was produced and that of this green matter, with plants in moist 
air, a large percentage occurred in the roots. In this, the aerial parts were 
richer in water. It was determined in regard to the functions, that evap- 
oration in moist air is absolutely less ; it is less also, however, per gram of 
green and dry matter produced, i. e. the plant in the production of one gram 
of material in moist air needs less water and this might occur because, 
under these circumstances, it produces it with few^ mineral substances. 

A further experiment with peas^ shows that the newly produced sub- 
stance has an actually lower percentage of ash. The increased amount of 
water taken up by the plant, because of the strong evaporation in dry air, 
results in the plant's taking up in a given unit of time only half as con- 
centrated a solution as it does with a weakened evaporation, when growing 
in moist air. 

These results explain sufficiently why plants in moist air frequently 
succumb more easily to disease than plants grown in dry air. The plants 
are weaker in growth, richer in water and poorer in ash. Nevertheless, we 
have no insight into the diversity of the organic elements in the plant body. 
It is very probable that plants grown in moist air are richer in sugar, 
poorer in starch, as well as richer in asparagin and poorer in actual protein. 

Influence of Moist Air on Plants Injured by Drought. 

It has been supposed that plants which have suffered from intense 
drought can be most quickly restored to their former activity if placed in 
a very moist atmosphere. The following experiment shows the danger of 
this procedure. Cherry seedlings, which survived a long drought in sand 
cultures, at once showed an adjustment to the lessened amount of w^ater 
supplied the roots. At first, without change of habit of growth, evaporation 
gradually decreased until the sand still contained possibly only 4 per cent, 
of the amount held when saturated. At this point the plants began to wilt, 
but, at the same time, evaporation ceased almost entirely. For example, 
at a temperature of 30°C. and abundant sunlight, a little plant which had 
formerly used daily about 8 g. water, evaporated only one decigram. After 
adding considerable water, the plant gradually increased the amount of 
evaporation. If, on the other hand, the drought continued too long, the 
leaves dried backward beginning at the tips, showing no discoloration. 

If now, after being watered, the plants were brought into moist air 
they did not recover as I had thought they would at first. Those under 
the bell jars containing dry air had elevated the upper mature leaves, and 
The partially dri'ed bases of the older leaves became turgid again ; evapor- 
ation again set in slowly. 

The gardener will find this observation of practical use in growing 
potted plants. Excessively dry plants after watering must not be changed 
in position. They must be somewhat shaded and they should not be placed 
in air practically saturated with moisture, since this will stop almost all 
activity. 

1 Loc. cit. p. 79. 



426 

Cork Outgrowths. 

Cork is universally formed as normal tissue. It may increase abnorm- 
ally, forming an excrescence under special circumstances. Even the regular 
formation of cork may be observed in varying amounts in different seasons. 
Attention should be given to the usual bark pores with their rounded com- 
plementary cork cells separated by intercellular spaces. These cells, show- 
ing for some time a cellulose reaction, are steadily reproduced during the 
time of growth. In winter, when the exchange of gases in the dormant 
bark is at its minimum, the production of the complementary tissue is 
stopped. In the autumn a layer of normal cork is formed from the cambium 
layer instead of the roundish complementary cork cells. With the awaken- 
ing of bark activity in the spring, the cork cambium again forms comple- 
mentary cork, rupturing the winter covering layer of the lenticel, just as, 
when the first lenticels were formed, it had split the epidermis. The more 
moist the air becomes, the more frequently the elongating complementary 
cork cells which attract water are formed on the surface of the bark. The 
longish, mealy, white excrescences, which may be rubbed off, are well- 
known. They occur on the smooth barked trunks of cherries and alders 
in damp habitats when the atmospheric humidity is increased and the fohar 
transpiration decreases. 

At the base of the strong petioles of Juglans regia, Sambucus nigra, 
Ailanthus glandulosa, Paulowna imperialis and other trees, in the autumn, 
structures may be observed very similar to lenticels, only the cambium layer 
is missing (Stahl)\ Later research- has shown that cork cushions not only 
develop at the base of the petiole but, in many plants, at the veins of the 
under side of the leaf {Ficus slipulata) and finally also on the leaf-blades. 

Now, although this formation of cork on the leaf-blade is a phenom- 
enon almost as widely distributed as that on the stems with which it closely 
corresponds in structure and development, yet, in spite of the wide distribu- 
tion, there is no pathological significance in these formations. 

In these cork outgrowths of leaves, two types may be distinguished^, 
either the cork layer with its dividing walls and its usually one-layered 
phellogen lies parallel with the leaf surface in the same plane,- — when the 
cork excrescences are raised above the surface of the leaf in the form of 
warts ; or the cork layer and especially its phellogen lies in the form of hour- 
glass-like, depressed zones in the interior of the leaf and usually becomes 
deeper and deeper. Many plants have both forms on the same leaf. In 
contrast to the regularity of the appearance and production of stem cork, 
emphasis should be placed on the accidental appearance of cork excrescence 
on leaves. Aside from the fact that the two above mentioned types can 
begin on the same leaf, there are also transitions between the two types. In 



1 Stahl, Entwicklungsgeschichte und Anatomie der Lenticellen. Bot. Zeit. 
1873, No. 36. 

2 Poulsen, Om Korkdannelse paa Blade. Kjobenhavn 1875. 

3 Bachmann, tJber Korkwucherungen auf Blattern. Pringsheim's Jahrb. 1880, 
Vol. XII, Part 2, p. 191. 



427 

fact, the cork outgrowths can arise in the same leaf in different layers (they 
usually occur in the sub-epidermal layer) and can have a different develop- 
mental course (Bachmann). 

The external appearance of these cork formations on leaves, occurring 
on gymnosperms, monocotyledons, and dicotyledons, is very different. 
Sometimes there are small cones, sometimes sheets of cork, or strips of 
considerable extent. " At times the cork excrescences, however, lead to the 
formation of holes which penetrate through the whole leaf (Ilex. Zamia, 
Ruscus, Camellia axillaris, Peperomia obtusifolia. Eucalyptus Gunni and 
E. Globulus, etc.). This perforation begins as yellowish points. In leaves 
with large intercellular spaces the cork formation is preceded by a growth 
of the parenchyma cells, in such a way that the intercellular spaces are filled 
by outpushings of the cell walls. If the cells with somewhat thicker walls 
in the rows of cork cells are changed by repeated division, the cell walls 
lose their original thickness. Frequently also the cork cells undergo a 
subsequent elongation after they have split the epidermis; the outer ones 
are stretched first. • 

In Zamia integrifolia, brown stripes, running parallel with the veins, 
are found on leaflets, splitting later into pieces or tearing down the whole 
length. These stripes are cork tissue which are not produced sometime 
after the leaflets have been torn and, thereby, representing wound cork, but 
are structures formed even embryonically in the younger leaf. Cork ex- 
crescences appear on both sides of the older leaves of Dammara robusta, 
but especially on the upper side, remaining usually small and flat. When 
young, they form small round spots on the green leaf surface and later be- 
come brown, when they are raised like little mounds. Finally, the epidermis 
and the immediately adjacent cork layers rupture. In Araucaria Ciinning- 
hami and more rarely in A. Bidwilli, small cork mounds may be found on 
older leaves of the previous year which can coalesce into ridges. In 
Sciadopytis verticillata and Cryptomeria japonica small cork warts occur 
at times also on older leaves ; such structures may be recognized more fre- 
quently (but usually only on the underside) on the broad leaves of Sequoja 
sempervirens. In commercial horticulture, small point-like cork warts in 
Cyclamen persicum form a blemish as do also the chart-like etchings on 
the upper side of leaves of Pelargonium peltafum and in different kinds of 
foUage Begonias. These cork outgrov/ths appear, so far as observed, only 
in moist greenhouses and hot beds. 

Among the monocotyledons, Clivia Gardeni, Hook and Clivia nobilis, 
Lindl., Pandanus reflexus, Dichorisandra oxypetala, Billbergia iridifolia, 
Vanilla planifolia, and other orchids exhibit cork structures which penetrate 
into the leaf. The cork excrescences on the leaves do not occur in the same 
amount in all specimens, nor to equal extent on all the leaves of the same 
plant, nor are the appearances constant each year. It must be concluded 
from this that special conditions cause this development of cork structures. 
So far as experience shows, they are due to an excessive atmospheric 



428 

dampness with a continued excessive supply of water at the roots and a 
decreasing intensity of hght. An insight into the production of these phe- 
nomena may be found in the 

Cork Disease of the Cacti. 

This disease, often found in imported cacti, has become a constant 
source of anxiety for the European grower. It manifests itself in the 
different varieties of cactus, in the appearance of dry, papery places. These 
begin sometimes as raised yellow spots, or as spots remaining green and 
looking somewhat glassy. They widen out either into large cork colored 
surfaces, or become depressions which look like the scars of places injured 
by biting insects or animals. My special studies were first of all with 
Ccrcus flagelliformis. In severe cases the tips of the stems still seemed 




t 



Fig. 70. Piece of the trunk of a Phyllocartius which, on its under side, exhibits 
"cork excrescences in the form of warts, while, on the opposite side, the 
process of perforation is beginning-. 

fresh and green, but at a little distance back from the tip a zone of rust 
colored specks began, starting usually below a thorn cushion. The specks 
gradually united into a rusty surface which ruptured here and there. 

On the healthy part, the outer epidermal tissue consisted of two layers 
of irregularly 4 to 6 sided cells with thickened, heavily cutinized outer walls. 
Under this double layer was a single row of cells elongated tangentially and 
thickened like collenchyma. Then came the bark tissue containing chloro- 
phyll and an abundance of crystals of calcium oxalate. Cork had been 
formed in the outer epidermal cells of the rust spots on the stems. The 
cork cells were wall-like in some places, irregular in others, like a cap which 
finally ruptured on the crest, thus rupturing the outer wall of the upper 
epidermal layer. 

In other Cereus species, different sides of the stem seemed whitish and 
dry in wide stretches. Here cork layers formed in the epidermal cells in 
the angle of the stem; these were raised like papillae, while on the surface 



429 







of the stems they were warts. In young spots a change hi the bark par- 
enchyma was noticed. The outer cells were no longer distinctly collenchy- 
matic and tangentially elongated but rather were broadened radially, thin- 
walled, poor in chlorophyll and partially divided. Because of this structure, 
the bark cells forced the cork tissue outward, causing whitish blisters or 
warts. 

In Opuntia and Phyllocactus, the second variety of cork outgrowth is 
prevalent and is characterized by the formation of depressed places or by 
total perforation. Fig. 70 of a Phyllocactus illustrates both forms of cork 
excrescence. On the under side we see wart-like convexities, on the upper 
side the beginnings of perforation. 

A cross-section of the flat stem shows the fleshy bark beyond the vas- 
cular Inindle. In healthy places the 
bark is hlled with starch (st) and con- 
tains numerous slime cells (s), cal- 
cium oxalate crystals and glands (0). 
when the wart begins to form, the bark 
parenchyma, by utilizing the starch, 
stretches, divides and pushes out the 
epidermis. The peripheral tissues (i) , 
poor in contents, begin to die and a 
layer of flat cork cells (/) separates 
the (lead tissue containing many inter- 
cellular spaces filled with air from the 
still living succulent tissue. At this 
])oint the progress of the disease stops 
and the stem seems covered with dry 
paper-like spots. If, however, there 
is no further removal of starch nor 
stretching of the bark parenchyma, and 
large particles die, the upper surface 

of the dead tissue finally ruptures, forming holes (/) which gradually be- 
come more and more depressed v/hile the flattened cork cells (t) are 
constantly formed, growing inward. At r the bark changed, giving rise to 
the cork formation. There the change occurred earliest and most intensively 
and advanced rapidly into the interior of the leaf. 

The process of cork formation is in itself a normal process in cacti 
when the stems reach a certain age. At the base of older stems there may 
be seen a formation of bark as in trees. The i)atliological feature is the for- 
mation of flat cork layers in the younger parts, at the expense of the bark. 
The cause may be found in the formation of tissue centers in the bark in 
which the cells elongate, while the starch breaks down and the cell contents 
are gradually impoverished. 

Fig. 71 shows the first change in the tissues, in the formation of bark 
types of cork excrescence. This illustrates a piece of bark from Phyllo- 




Fig. 71. First stage of a cork 
excrescence in Phyllocactus. 



430 

cactus with a spot dififerentiated from its healthy surroundings by a scarcely 
perceptible yellowish discoloration and a very slight convexity : e, indicates 
the epidermis ; I, the collenchyma-like thickened cells ; o, the crystals of 
calcium oxalate. The change begins close to the vessels i^g) in the delicate 
venation traversing the succulent parenchyma. The darker spots in the 
parenchyma indicate the chloroplasts, which are found there either in the 
normal position along the walls, or collected in large refractive drops of 
cell contents (o'). Probably as a result of an accumulation of destructive 
enzymes and an increase in acid content, the sheath cells of the vascular 
bundle {gs') and those even further away ii) become poorer in contents and 
elongate, thus causing the first evidences of disease. Thus an inner growth 
is produced which, if it advances nearer to the upper surface, starts the for- 
mation of cork. If the cells, extending further back into the inner bark, 
become impoverished, more and more cork will be formed. Since the cork 
tissue cannot elongate as the organ grows, it must be of necessity rupture, 
and thus forms superficial warts as the cork formation advances. Grooves 
are formed by the strain of the tissues growing with varying rapidity and 
these deepen until there is a complete perforation as in deep scurvy of 
potatoes. 

In order to control or eradicate this important disease of cacti, the 
water supply is lessened and air is given abundantly. Should there be a 
regular appearance of the disease covering several years, the plants must 
be kept dry even to shrivelling. 

Bitten or Perforated Leaves. 

In herbaceous plants, as also in trees in different localities, the leaves 
are often strongly perforated as if some animal had eaten away the tissue 
between the veins, without, however, finding any animal on whom the 
blame may be laid. Since the injuiy increases in intensity with time, ob- 
servers are more eager to find the cause. In extreme cases the injury is of 
such extent that the leaves appear like many paned windows, since only the 
network of veins remains together with a slight margin of leaf parenchyma. 
.Such leaves are often bent and twisted but do not die prematurely. The 
shoots themselves show no disease and frequently new sprouts with normal 
foliage develop in the axils of these perforated leaves. 

The most extreme case which I have had opportunity to observe was 
found in potatoes. The shoots of the plants at the beginning of July bore 
only perforated leaves (see Fig. ^2). Usually the lower leaves w^ere per- 
forated only in places, the upper ones w^ere split longitudinally in the areas 
between the veins and frequently parts of the edge were also destroyed. 
The younger leaves often had a feathery appearance since the different 
leaflets consisted only of the veins with a very slender margin. 

Between the perforations yellowish points were seen in the leaf-blade 
when held to the light. These proved to be the first stages of the process of 
suberization w^hich ended wdth the perforation of the leaf. The formation 



431 

of cork took place in the way described in the preceding general section. 
It was proved, however, to be a secondary phenomenon. The disease first 
manifested itself in the pale green color of the mesophyll usually near the 
finely anastomosing veins. This appeared more frequently in the palisade 
than in the spong}' parenchyma. In isolated cases, instead of becoming 
pale, the cell contents discolored to a brownish tone which was accom- 
panied by the suberization of the walls. The epidermis, in its changes, 
followed the mesophyll groups and small dead tissue centers were produced 
which did not change any further. 

In the group of cells forming the transparent places in the leaf because 
of the dissolution of the chlorophyll, an enlargement was seen on account 




Fig. 72. Potato leaf perforated as a result of a morbid formation of cork. 

of which the non-participating epidermis was pushed outward. A cork 
formation now set in among the enlarged mesophyll cells ; then these places 
broke out. By the advance of these processes backward into the flesh of 
the leaf, the cork centers were depressed to complete perforation. This 
can be understood easily since young leaves are affected. In their growth, 
these stretch all the tissues; since the tissues containing cork cannot stretch 
with the other tissue, they must tear. 

The process, therefore, is, in principle, that found on the stems of 
cacti. 

In other plants also, which show perforations of the leaves, the im- 
poverishment and enlargement of difi^erent cell groups may be recognized 
as the early stages and, on this account, naturally belong to the phenomena 



43-' 

which will later be described as intumescences. The causes will also be 
taken up more in detail then. 

In the production of the perforations, individual nutrition plays a 
prominent part; for, in the same place of growth, specimens which seem 
almost eaten up, may be found near plants which remain untouched. At 
times, only isolated species suffer. Thus, for example, I found in groups 
of different species of maple only one single vigorously growing variety 
which was diseased, among other kinds developing noTmally. 




Formation of Cork on Fruits. 

The brown, dull, not infrequently scaley spots or lines on the smooth 
outer surface of apples and pears, the so-called rusty tracery is well-known. 
Some varieties show the phenomenon every year, so that it has been in- 
cluded in the general description of the species. They are formations of 

cork, which, as a rule, arise from the 
stomata. In some years the process be- 
comes abnormal in its appearance, so that 
not on]}' "the varieties with rust spots" 
have a |)artia] or entire cork-colored sur- 
face, but also the fruits of varieties 
usually remaining smooth-skinned are 
affected. 

Injuries to the epidermis when the 
fruit hrst swells are the cause of this phe- 
nomenon. In cases already known to me 
(apples, pears, plums, grapes), it could 
be proved that a light late frost had split 
the cuticle covering of the young fruit in 
innumerable small tears. Under these 
the fruit at once formed cork layers. 
In places the epidermal cells die and remain together with the first formed 
cork layers as scales on the rather dull, leather colored surface of the fruit. 
Whenever the corked places form a contiguous surface, the fruit in 
development does not swell uniformly, with the result that huge splits show 
on the fruit itself. The spores of Monilia especially enter these places and 
mummify the fruit. 

But these phenomena, in the strictest sense, do not belong here. They 
are connected with an excess of moisture only in so far as the splitting 
occurs the more easily, the more quickly the swelling of the fruit takes 
place with continued moisture. 

On the other hand, I would like to consider the appearance of cork warts 
on the stems of grapes as a process which becomes noticeable only in moist 
air. In Fig. 73 we see two grapes, the stems of which exhibit a browned rough 
surface due to the appearance of many cork-colored, closely distributed warts. 
The phenomenon occurs before the grapes have reached their normal size. 



Fi£ 



73. Grapes with cork warts 
(W) on the fruit stem. 



microscopically small splits. 



PART VI. 



MANUAL 



OF 



Plant Diseases 



BY 



PROF. DR. PAUL SORAUER 



Third Edition—Prof. Dr. Sorauer 

In Collaboration with 

Prof. Dr. G. Lindau And Dr. L. Reh 

Private Docent at the University Assistant in the Museum of Natural History 

of Berlin in Hamburg 



TRANSLATED BY FRANCES DORRANGE 



Volume I 
NON-PARASITIC DISEASES 

BY 

PROF. DR. PAUL SORAUER 

BERLIN 



WITH 208 ILLUSTRATIONS IN THE TEXT 






Copyrighted. 1916 

By 

FRANCES DORRANCE 



P'- 



JUL 1 1 1917 



THE RECORD PRESS 
Wilkes-Barre, Pa. 

©CU470231 



433 



The warts are developed most abundantly at the place where the grapes 
join the stem: large branches of the clusters usually remain smooth and, 
as a rule, only some grapes show the disease. This is unimportant in con- 
tinued dry weather, but with humidity makes for a development of parasites. 
If then a sharp dr}- period follows, some of the \er}' warted stems shrivel 
and the grapes as well. 

Fig. 74 shows a cross-section through a warty grape stem which exhibits 
the usual axillary structure and has some strikingly broad medullary rays 
(ms) which divide the wood ring (h). In the bark we notice a regular 
distribution of the hard bast groups (b) and in front of them the sieve 
elements (.v) with often thickly swollen walls. At o is indicated one of the 
abundant crystals of calcium' ox- 
alate. These occur at times as 
small glands, at times as raphides. 
The dififerent stages of the forma- 
tion of these corky warts are 
shown at JV. The wart-like ex- 
crescences, which resemble len- 
ticels. are produced by the radial 
enlargement of some of the par- 
enchyma cells lying immediately 
beneath the epidermis or some- 
what deeper; and the consequent 
outpushing of the outer skin. By 
an increase of this process, which 
does not preclude the dividing of 
the elongated cells, an accumu- 
lation of tissue is produced with a 
corky covering which finally be- 
comes brow^n and splits. By the 
increase of the bark parenchyma 
and the dying of the outermost 
brown corked elements the large 
warts are produced, the peripheral cell layers of which are pushed out from 
each other in a saucer-shaped form. A distinct cork cambium is formed 
connected with the dying bark of the outermost layers. This constantly 
extends deeper into the bark of the stem. If the weather continues to be 
cloudy, warm and damp, or if the grapes are too much hidden under the 
foliage, the conditions are ideal for the development of fungi among which 
may be noticed first of all Botrytis cinerea. 

The phenomenon is especially frequent in greenhouses, and here the 
close, moist atmosphere must be improved by ventilation and heat must be 
provided at the same time. If the warty grape stems are found out of doors, 
some of the foliage above the bunches of grapes must be removed and, after 
each rain, the water retained by the foliage carefully shaken off. 




74. Cross -section through the warty 
fruit stem of a grape. (Orig.) 



434 

As a phenomenon related to cork excrescences, I once observed wings 
on young grape leaves. These appeared between the larger side veins on 
the leaf blade and were opposite each other like lips. These outgrowths 
(emergences) were a development of the blade usually forming over a 
vascular bundle. 

The chagrinisation (granulation) of the rose stem should be cited here 
in addition. As is well known, standard roses are laid flat through the 
winter and covered with brush or earth. At times in the spring when 
these are raised from the soil, the young bark stems, which should be 
smooth, are often found covered with small warts, many having, as a rule, 
a pale or brownish-red periphery. The warts are outgrowths of the lenticel. 
These begin below the stomata and force the guard cells apart. Mycelia 
may be proved to be present if the periphery is discolored. 

Yellow Spots (Aurigo). 

At times the leaves of monocotyledons, more than those of dicotyledons, 
are covered with yellow or reddish brown specks. This speckled condition 
begins at the tip. The specks usually shade through a pale green zone into 
the otherwise normally green leaf. Their number may be increased, since, 
as the disease progresses, small new specks are formed between the older 
ones. At times the tissues affected in the discoloration are forced out, 
which shows a clear transition to real intumescences^. 

This yellow spotting occurs especially in greenhouse and house plants, 
and among these, we find it most frequently in Dracaenae, palms and varie- 
ties of Pandanus. 

To illustrate the formation of these specks and show how, under certain 
circumstances, they increase until the leaf is perforated, I will cite some 
observations on Pandanus javanicus. 

The spots always begin in the part of a mesophyll lying between two 
veins. Toward the upper side of the leaf these cells resemble the palisade 
parenchyma, on the under side, spong)^ parenchyma, but in the centre they 
are very thin walled, approximately isodiametric, somewhat hexagonal, 
filled with a colorless watery content. 

From the innermost colorless tissue groups, the peripheral cells, i. e., 
those bordering on the mesophyll, containing chlorophyll, begin to stretch 
excessively toward the side of the least resistance, viz., toward the centre, 
whereby they frequently compress the central cells. Frequently the elon- 
gatioin takes place only in the cells arranged directly upward and downward, 
but not in the lateral ones of the thin-walled group, and a peculiar arrange- 
ment is thus produced. The central part of the tissue then consists of empty 
cells arranged radially, elongated like pouches, which often have become 
thick-walled by swelling, later browning and turning to cork. With 
increasing intensity, the spongy parenchyma is involved in this process of 
elongation with the dissolving of its chlorophyll body; its contents disinte- 

1 Vol. 9, Part 5. 



435 

grate 'into a brown granular substance, and in this the yellow coloration 
becomes more intensive. The upper surface of the leaf is often raised like 
a wart when the tissue, rich in chlorophyll, is drawn into the abnormal 
process of elongation. 

Frequently the progress of the disease is stopped when the elongated 
cells become cork, then there are only yellow spots, recognizable when 
immature, indeed, only when the light falls through them. The whole 
centre of the disease may then be separated from the healthy tissue by a 
zone of actual cork cells. As the disease advances in severity even the cells 
of the vascular bundle sheath may be affected and show the characteristic 
elongation, browning and swelling until finally the elongating mesophyll 
cells rupture the epidermis above them. The processes already described 
under the phenomenon of perforation nov; follow. Diseases due to fungi 
and seemingly similar in outward appearances may easily be distinguished 
in Pandanus, since in them there is no elongation of the cells. In Dracaena 
rubra and Draco, the disease at times only disintegrates the chlorophyll of 
the inner cell groups ; here membranes are often seen with bead-like swollen 
places extending into the inner part of the cell. In studying Dracaena 
tndiz'isa, I observed an abundant formation of sugar in those tissues in which 
the chlorophyll had dissolved. This sugar did not occur in healthy tissues 
and disappeared from the diseased spots as soon as the walls began to turn 
brown and develop cork. 

Hence this yellow spotted condition seems in many cases to be an 
initial stage of real intumescence, in others, as in the Dracaena, it is usually 
a diseased condition without any sequelae and the temporary increase of 
sugar and the bead-like swellings of the walls point to causes which are 
similarly affective in the over-elongation of the cells. In practical treatment, 
one should realize that the plants exhibiting aurigo suffer from a supply of 
water which they cannot assimilate. The amount of water destroying the 
equilibrium need not be greater than that normally supplied, but, being given 
during the dormant period, the plant cannot utilize it and the external con- 
ditions are not such as could stimulate this absorption. The spots occur 
with great frequency in the autumn and winter when the plants are brought 
into a warm place. They then have sufficient heat, water and mineral 
nutrient substances, but the light is deficient. Hence the one-sided stimulus 
must be removed and the plant put in a cooler, dryer place where there is as 
much light as possible. 

Intumescences. 

The knot-like or pustule-like distensions of the tissue usually occurring 
in groups and which I have considered as "Intumescentia" have not been 
sufficiently studied by practical pathologists. They are most abundant in 
leaves but are not rare on the stems. However, as yet, the observation of 
intumescences on blossoms and fruits has been limited. 

The consideration of a specific case gives the best information as to the 
development of such structures, the value of which lies in their symptomatic 



436 

significance. In January, 1879, I observed specimens of Cassia tomentosa 
in a hothouse. I found the edges of leaflets on young shoots were curled 
under. This curhng seemed to be due to the increased growth of the upper 
side, which showed a pustule-like convexity. When these convexities were 
fewer and located along the mid-rib, the leaflet was less curled. If they 
were scattered abundantly and uniformly over the whole surface, the leaf 
seemed almost blistered. This cannot be said to be actually blistered, how- 
ever, because the convexity of the upper side corresponds to no equally 
great concavity of the underside. 

The swelling is conical, having, at first, the same color and dull upper 
surface as the rest of the leaf. Later the tip of the cone becomes light 
colored, more rigid and shiny. Still later the tip becomes yellow, broadens 
and finally ruptures (Fig. 75, se), if the whole leaflet has not already turned 




Fig-. 75. Leaf intumescences in Cassia tomentosa. (Orig.) 

yellow, the swelling now seems depressed in the centre, funnel-like, and 
turns brown. 

The phenomenon is due to a sporadic tube-like outgrowth of the upper 
palisade parenchyma (p). The inner side contains many chloroplasts closely 
packed together and, toward the spongy parenchyma, is provided with 
slender, slit-like intercellular spaces filled with air. 

With the appearance of swelling, the chloroplasts begin to disappear 
from the tip of the cell backward, a few of the cells become elongated; 
gradually the surrounding tissues are involved. More and more chlorophyll 
is dissolved as the elongation advances, so that finally the palisade cells, 
which have become tube-like, seem almost entirely colorless or are provided 
with a few small yellowish grains scattered throughout the whole cell lumen. 
With this elongation of the cells forcing up the epidermis there is a slight in- 
crease in width, which presses the cells very^ close against one another 
laterally, with only small intercellular spaces in the spongy parenchyma. As 



437 



soon as this pressure has ruptured the epidermis (e) at the highest point of 
the excrescence {^e) the ends of the paHsade parenchyma, which are now 
freed, swell up hke clubs (kp) and, turning brown, thicken their walls more 
or less farther back. The epidermal cells which are ruptured, and others 
in the same region, turn brown and partially collapse. 

The same swelling can also occur on the side of the leaf. In this case, 
the spongy parenchyma cells lying directly beneath the epidermis, covered 
with hairs (h) and otherwise usually isodiametric, become long and 
cylindrical. 

In various epidermal cells of the upper as well as the lower side of the 
leaf and in many of the parenchyma cells which have grown out like tubes, 
glycerin draws together in indi- 
vidual large glucose drops or many 
small ones. 

I found similar leaf distensions 
in Acacia longi folia and A. micro- 
botrya leaves specked with yellow 
and also on those normally green. 
Myrmecodia echinata is an ex- 
ample of the general appearance of 
intumescences with cork leaves. 
The leaves of this plant usually de- 
velop intumescences on the lower 
side, while the cork excrescences 
predominate on the upper side. In 
Fig 76 we perceive that actually 
both of the parencyma layers lying 
next to the epidermis participate in 
the formation of the delicate gland- 
like outgrowth of the tissue. The 
epidermis (c) (its stomata are un- 
changed) is raised up and ruptured 
where it joins the normal tissue. 
Strange to say, however, it appears 

to be still unbrowned and turgescent, i. e., still completely and sufficiently 
nourished like the tube-like mesophyll cells (a). I found that the excres- 
cences had dried up and had been cut ofT from the healthy parenchyma by 
the formation of the layer of flattened cork cells at their base (b) only 
when the leaf was well advanced in age. 

The partially blister-like, partially wart-like cork excrescences are most 
frequently found without intumescences. They are distributed irregularly 
over the whole leaf surface as rusty, sometimes silvery shining specks; the 
region of the mid-rib is most affected. 

The cork forms first within the epidermal cells, advancing thence into 
the mesophyll, attacking at first two adjoining layers of the hypoderm. 




Fig-. 76. Piece of a leaf of Myrmecodia 
echinata with a cork wart breaking out 
on the upper side and gland-like intu- 
mescence on the under side. (Orig.) 



438 

formed of four or five rows of colorless cells with very wide lumina but 
poor in contents (d). The underlying palisade parenchyma, extending into 
the hypoderm in the conical-Hke buttresses (e) is usually not affected, but, 
like the spongy parenchyma, poor in chlorophyll, often exhibits strongly 
refractive, often green colored drops in its cells where the cork is formed. 

Often such corky masses very greatly resemble certain fungous dis- 
eases as I have had opportunity to observe in Pelargonium zonale. 

The under sides of the leaves were covered with white cystopus-like 
masses, isolated or united into large groups. These were hemispherical 
cork excrescences, later separated from one another like fans and filled 
with air. They began with an enlargement of the spongy parenchyma, 
whereby all the intercellular spaces were filled up. The epidermis, as a 
rule, remained unchanged while the mesophyll cells adjoining it were elon- 
gated perpendicularly and were divided by cork walls, with a gradual loss 
of chlorophyll. The cork cells partially lost their parallel arrangement 
because of an irregular increase and were much distended until the epidermis 
ruptured. The epidermis, however, manifested its restraining influence by 
pressing upon the cork cells, so that their walls seemed crumpled. The 
process of elongation and suberization extended deeper and deeper into the 
mesophyll until at times the excrescence was four times as thick as the leaf. 
A brown, twisted mycelium (possibly a Cladisporium) grew into the stomata 
and later into the wound of the rupturing cork excrescence. 

Grapes are especially susceptible to intumescences and especially those 
plants taken from greenhouses into the open for early forcing. In addition 
to the excrescences on the leaves, little knots were formed on the stem of 
the grapes, and, since the structure of these dift'ered from the warts already 
described, they may be considered here more thoroughly. 

Fig. yy is a cross-section through such a knot. The vascular bundles, 
forming the wood-ring of the stem, are indicated by h, the pith by m; the 
hard bast by hh ; the abnormal change in the bark parenchyma extends to 
this point. This change is characterized by a distension of the parenchyma 
lying underneath the coUenchyma-like elements and an ultimate elongation, 
the cells of which have subsequently divided. Because of this over elon- 
gation the coUenchyma {c) is pressed together and, without previously 
having participated in the elongation, dies together with the epidermis. The 
normal epidermis may be recognized 2it e; k indicates the cork zone formed 
on the boundary of the dying tissue. The latter may not always be found, 
however. Often the dying tissue passes over imperceptibly into the very 
thin-walled, still living tissue which shows slight cork formation at the place 
of transition, eg indicates the normal collenchyma, occurring in groups and 
not in connected rings. The division and over-elongation of the bark 
parenchyma and the absence of cork excrescences distinguish these knot- 
like intumescences from the cork warts which, in an immature stage, 
resemble them greatly. 



439 

The intumescences on grape leaves have on the under side the form of 
iand-Hke elevations which often coalesce and are indicated on the upper 
leaf surface by yellowish and at times somewhat raised places. They are 
produced by tube-like outgrowths of the spongy parenchyma lying under 
the epidermis ; the cells of this spongy parenchyma are poor in solid con- 
tents and closely pressed against one another b}^ the distension. With their 
increasing over-elongation, the epidermis is browned and ruptured. 

In the beginning only the cells lying directly beneath the epidermis are 
affected, but usually, after the distension begins, the cell layer next below 
is attacked and it is usually this which later is most elongated and its cells 
not infrequently divided by cross walls. The cells forming the centre of the 
swelling are the longest and most slender and stand exactly perpendicular to 
the outer surface of the leaf, while those laterally adjacent are arranged 




Fig. 77. Part of a knot-like intumescence on the stem of a gi'ape. (Orig.) 

slantingly like a fan, decreasing in length, increasing in width. The presence 
of starch could not be proved. In the most extreme cases observed, all the 
cells of the mesophyll, up to the palisade parenchyma of the upper side, take 
part in this elongation. I did not observe, however, that the palisade 
parenchyma had been attacked. 

These intumescences are not infrequent in vineyards and cases may be 
found showing their cause most clearly. In the course of years material 
has come most abundantly to my hands. I quote from the report of the 
court gardener, Mr. Rose. 

He had a grape house planted with 14 vines; of these, six were Black 
Hamburgs (Blauer Frankenthaler), one of these was planted where the hot 
water pipe entered. Therefore, the temperature was higher and the humid- 
ity very great. 

This vine alone developed intumescences to such a degree that the 
under side of the leaves seemed almost felty. A Royal Muscardine vine 



440 

was planted on the opposite side of the greenhouse. The foUage of these 
two plants became intertwined as they grew into the upper part of the house. 
The Royal Muscardine plant had no trace of disease. 

These instances show how differently varieties behave in the same 
environment, and how individual diseases in the same variety may be 
explained. 

In regard to the dift'erent behavior of dift"erent vines, reference should 
be made to a study by Fr. Muth\ who observed the production of intu- 
mescences after spraying the leaves with copper compounds, while, for ex- 
ample, the early red Veltliner and Muscat St. Lauret show no sweUing. 
Morillon panache, Madeleine Angevine and the Blue Ox-eye were very 
greatly affected. 

In another similar case, Noack- found that the disease decreased when 
water was withheld. 

The occurrence above described does not correspond with the phe- 
nomena found on Ampelopsis hederacca". In this plant Tomaschek found 
bead-like structures on young branches, petioles and leaf veins, and espe- 
cially on the outer side of the side leaves. The beads were very small when the 
illumination w^as insufficient and dried up in the autumn. They were formed 
below the stomata even in the very young parts, since the cells surrounding 
one cavity grew down into it and forced up the epidermis by an increase 
in size. In the autumn and winter true lenticels with a cork formation were 
found, instead of these outgrowths. 

In addition to the instances already described and those to be men- 
tioned further on of disease manifesting itself on greenhouse plants, I will 
now report on the behavior of one of the Gramineae. 

On the island Riigen, among vigorously growing oats, plants were found 
showing abnormal growth. A cross-section of the lowest node, covered 
with dirt, is illustrated in Fig. 78. The centre of the node exhibits the well 
known irregular course of the vascular bundles (g) and the primordia of 
a root (w) ready to break through the distended bark of the node. In this 
bark covering r indicates the normally formed part, while at r' the subepi- 
dermal parenchyma cells are already beginning to elongate radially. The 
excessive elongation increases at j to a decidedly tube-like character and 
affects all layers of the bark near the root just coming through. This dis- 
tends the epidermis very greatly, and, as its cells do not take part in the 
process of elongation, it finally begins to separate in different places (c). 
The leaf blade at s shows an external injury from grazing cattle which 
extends deep into the node. The tissue is considerably browned, the 
vessels, as far as the middle of the node, are partially filled with gum. The 



1 Muth, Fr. tjber die Beschadigung der Rebenblatter durch Kupferspritzmittel. 
Mittel. d. Deutsch. Weinbau-Vereins 1906. 

2 Noack, Fr., Fine Treibhauskrankheit der Weinrebe. Gartenflora 1901, p. 619. 

3 Tomaschek, tJber pathogene Emergenzen auf Ampelopsis hederacea. Osterr. 
Bot. Zeit. 1879, p. 87. 



441 

facts warrant considering this injury the exciting agent in the formation of 
intumescences. Other adjacent blades which have not been similarly 
injured, do not develop the excrescences. The assumption can be very 
easily made that, given an abundant supply of water and nutritive sub- 
stances, the turgescence in the stem would be great, while the evaporation 
from the node covered with soil would be slight and an injury from grazing 
cattle which would remove part of the tissue, would so increase the turgor 
that intumescences would be formed. 

I had already observed similar correlation phenomena in the action of 
copper sprays on potato leaves^ In vigorously growing varieties a number 
of leaves were found injured by the spray; near the dead spots in the tissue, 
the intumescences later appeared. Still other causes may have similar 




9 r ,g 

Fig. 78. Intumescence on the lower node of an oat plant. 

results, since small warts have been observed on potato leaves when the 
copper solution had not been used-. Von Schrenck^ has reported more 
recent results in this connection. A few days after cabbage plants in green- 
houses had been sprayed with copper ammonium carbonate, pale knots, 
gradually becoming white, developed on the under side of the leaves. They 
proved to be intumescences. Unsprayed plants in the same house showed 
no eruptions. Spraying with weak solutions of copper chlorid, copper 
acetate, copper nitrate and copper sulphate did cause some distensions. Von 
Schrenk, however, considered these intumescences a reaction of the leaf 
tissue to the chemical stimulus of the poisons, not correlative phenomena. 

1 Sorauer, P., Elnige Beobachtungen bei der Anwendung von Kupfermitteln 
gegen die Kartoffelkrankheit. Zeitschr. f. Pflanzenkrankh. 1893, p. 32. 

2 Masters, Leaves of potatoes with warts. Gard. Chron. 1878, I, p. 802. 

3 Schrenk, H. v., Intumescences formed as a result of chemical stimulation. 
Sixteenth ann. report Missouri Bot. Gard. May, 1905. 



442 

Here belongs the case which Haberlandt^ describes in a Liane, Cono- 
cephalus. He describes the formation of compensatory hydathodes, after 
the normal organs of the leaves have been poisoned. The extremely 
abundant nocturnal transpiration takes place at the base of the shallow 
depressions on the upper side of the leaf by means of sharply differentiated, 
epithemial hydathodes with water pores always lying over the juncture of 
vascular bundles. Where these organs had been poisoned by painting the 
leaf with a 0.5 per cent, alcoholic sublimate solution, small knots were 




Fig. 79. Stem of Lavetera trimestris 
— with intumescence. (Orig.) 




Fig. 80. Brancii of Acacia pendulata — 
witli intumescence. (Orig.) 



Fig. 81. Magnified section of Fig. SO. 
(Orig.) 



formed above the vascular bundles. Each morning large drops of water 
were found. on these places. These knots, which had assumed the function 
of the dead hydathodes, seemed to be composed of long, pouch-like cells, in 
the lower part divided by cross walls adjoining one another (without inter- 
cellular spaces). The club-like swollen ends separate from one another 
like a brush. They have been produced by the elongation of the conductive 
oarenchyma cells and often of the palisade cells and have broken through 
the epidermis. 



1 Haberlandt in "Festchrift fur Schwendener," cit. in Naturwiss. Woclienschr. 
1899, p. 287. 



443 

Fig. 79 shows the habit of growth of a piece of Lavatera trimestris 
stem with excrescences due to cell elongation. Fig. 80 shows the rup- 
tured bark of Acacia pcndxila, while Fig. 81 shows the same much more 
clearly because of its magnification. 

In Malope grandiflora and Lavatera trimestris, stems and branches 
were found bearing many long calhises on the side exposed to the sun. 
These were caused by considerable longitudinal and radial stretching of the 
bark and wood cells. If the callus is still young, the process usually sets in 
by a radial and still more marked tangential stretching, at the level of the 
primary hard bast bundles of the parenchyma cells containing chlorophyll 
and lying between two bundles : with this increase they are pushed outward 




Fig. 82. Cro.ss-section through a year old branch of Acacia pendula with 
intumescence. (1-433).) (Orig-.) 

like a bow. The mechanical ring appears to be broken because the bast 
bundles are pressed far apart and the collenchyma layers less developed. 
In large intumescences the broken places apparently extend deeper since 
the wood also changes its prosenchymatous elements and the cells of its 
medullary rays into a wide meshed parenchyma. 

Fig. 82 throws sufficient light on the processes concerned in the forma- 
tion of the moss-like collection of intumescences in Acacia pendula; m 
indicates the pith ; h the woodring ; c the cambium ; h the hard bast groups ; 
e the epidermis ; s the beginnings of elongation within the primary bark ; zv 
the bark parenchyma cells which have become tube-like and ascend in 
spirally parallel roM^s and, after breaking through the epidermis at w, 
separate from one another like sheaves. 



1) Sorauer, P., tjber Intumescenzen. 
S. 458. 



Ber. d. Deutsch. Bot. Ge.s. 1899, Bd. XVII. 



444 

When the intumescence is highly developed, the over-elongation extends 
backward to the secondary bark, stretching the cells of the phloem rays (q). 
In fact, cases occur in which the woodring seems stimulated in those layers 
last formed because the outermost cambial layers are constructed of paren- 
chyma wood. As on the various kinds of Eucalyptus, the intumescences 
occur most frequently on the side of the branch turned toward the light, 
and often only then. After the explanation given these cases, a more 
thorough discussion is needed here. 




Fig. S3. Blossoms of Cymbidium Lowi with gland-like intumescence (a) on the 
tops of the perianth. (Orig.) 

Intumescences occur most rarely on blossom organs. I observed one 
such case in Cymbidium Lowi. The blossoms, normally large and otherwise 
well-developed, exhibited on the under side of the perianth, quince yellow or 
yellowish green, hemispherical bosses (Fig. 83a) ; exactly the same struc- 
tures could be found also on the ovaries. In an immature stage they had 
a smooth upper surface, later they cracked open in the apical region and 
became depressed like a funnel. In the older knots, the depression advanced 
to complete perforation of the perianth tip. For this reason the blossoms 
were unsalable. In Fig. 84, it may be seen that the cell layer found beneath 



445 

the epidermis (e) of the under side of one part of the perianth has devel- 
oped erect, club-Hke tubes, at first bent toward one another hke lopped 
trunks (s), which first had been held together by the brown-walled, swollen 
epidermis not afl:'ected by the stretching. After the epidermis had ruptured, 
the tubes, which were rather thick walled, deep brown and had lost their 
contents, separated from one another like sheaves. The process of the 
over-elongation gradually attacks the deeper and deeper lying parts of the 
cell and finally advances even directly to the upper epidermis (w). At this 
time the epidermis ruptures and the tips of the perianth tip^ become 
perforated. 

The first stages of the intumescences have been studied in the ovaries. 
The first symptoms are a localized change in 
the epidermal cells, the walls of which are yel- -^ 

lowish brown, and swollen. These cells extend 
over«the upper surface. Beneath these places 




Fig. 84. Cross-.section througrh an intumescence on the perianth of Cymbidium 
Lowi. Upper figure, young stage; lower figure, mature condition. (Orig.) 

O upper side. C under side, e epidermis, i- (upper figure) beKiniiiiiR of elongation of the sub-epidermal cells, 
J (lower figure) the rupturing of the chib-like over-eloug ited cells, g vascular bundled. zt> av.mced 

condition of perforation. 



the tissue is perfectly colorless, more closely pressed together and filled more 
abundantly with protoplasm and oily looking drops. In some of these places 
a radial stretching has already taken place, which increases up to a diagonal 
inclination and cross-division. The process gradually extends to the sur- 
rounding cells, especially to those lying directly beneath the epidermis. The 
elongating layer becomes strikingly thick-walled and turns cofifee brown, 
while the collapsing, swollen epidermis forms a light yellowish brown cap. 
The discoloration is accompanied by a process of suberization, and to this 
probably may be ascribed the fact that the cells, becoming brittle in the still 



1 Sorauer, P., Intumescences an Bliiten. Ber. d. Deutsch. Bot. Ges. 1901. 
19, p. 115. 



Vol. 



446 



incompletely developed organs affected during their elongation, rupture and 
crumble. This is the beginning of the funnel-like depression at the tip of 
the intumescence. 

Among fruit intumescences, I have most frequently observed the unripe 
pods of beans and peas and noticed that many varieties of fungi infested 
the pods. The fruits, especially when near the surface of the soil, seemed 
closely covered with warts and awakened the suspicion of a marked fungous 
infection, as may be seen in the pea-pod shown in Fig. 85. 

•In cross-section, it may be seen in different places, which still seem 
smooth to the naked eye, that some epidermal cells have already begun to 

elongate. These often lie directly beside the 
stomata, but without the cooperation of the 
stomata in producing intumescences. Gradu- 
ally the parenchyma cells lying below be- 
come elongated. The elongated elemerfts are 
often divided by cross-walls and form warts. 
However, these are first formed of rows of 
cells arranged like columns. These warts 
grow to a height of one millimeter ; later they 
become brown from the dying of the peri- 
pheral layers and, after the covering splits, 
the rows of cells spread out like a sheaf. 

Fig. 86 shows the greatest development. 
The normal wall of the pod is shown at fr; 
c indicates the epidermis ; P layers of the 
thick-\\alled partially intersecting elements 
of the inner parchment-like fruit membrane. 
In the centre of the outgrowth {w) the 
elongated columnarly arranged parenchyma 
cells, separating toward the outside, irregu- 
larly like a fan, are visible. The outermost 
peripheral zones, shaded in the drawing 
{z, z), indicate the moribund tissue. The 
walls of these collapsed parenchyma groups, 
often shrinking together in curling tips, seem 
yellow to brown and give the warts an earthy color. From the repeated 
splitting of the intumescences, which are often so close to one another that 
only a few normal epidermal cells separate them, the whole wall of the pod 
obtains in places a mossy outer surface. 

The parchment-like inner wall of the pod forms intumescences ; indeed 
this is. more frequently the case than on the outer wall. In some kinds of 
peas, with very pithy pods, white tissue felts resembling species of mold 
may be found almost every year on the firm, smooth inner surface. In one 
case in the intumescence tissue, I found numerous oospores which presum- 
ably had belonged to Peronospora Viciae. 




Fig-. 85. Pea-pods with gland- 
like raised outer surface. 
(Orig.) 



447 




mcr- 






'^:. 



f^ 



From the examples already cited it is evident that the intumescences 
may occur on all aerial organs of plants. They form one link in a chain of 
phenomena which in part commonly occur together and in part, in fact, 
overlap. We have described the simplest disturbances as "Aurigo ;" they 
are characterized by the impoverishment of some tissue groups in the 
interior of the leaf with a destruction of the chlorophyll apparatus, usually 
with the formation of carotin. As the chlorophyll disappears the cells are 
apt to become distended. They fill the intercellular spaces, thus exercising 
pressure on the surroundings ; they finally die as the cell walls become 
suberized. Such nests of over-elongated cells are also termed "internal 
intumescences." In real intumescences the processes of impoverishment 
and cell elongation begin in the peripheral layers of the organs and in fact 
usually in the sub-epidermal 
cell layers, more rarely in 
the epidermis itself. The 
process of over-elongation 
is less impeded here and 
frequently advances into 
the more deeply lying tis- 
sue layers, so that we find 
cases of intumescences be- 
ginning on the under side 
of the leaf and gradually 
including the whole meso- 
pliyll as far as the upper 
epidermis. If the forma- 
tion of cork sets in in the 
intumescence tissue, we find 
wart-like or pitted cork 
centres which can lead to 
the complete perforation of the leaf. 

On the trunk the intumescence manifests itself in the hypertrophy of 
the bark parenchyma which, in isolated enclosed centres, breaks out from 
the bark in the form of warts with a smooth or repeatedly split outer sur- 
face. If the processes of over-elongation are not restricted to small isolated 
centres but attack the parenchymatous tissue in large, connected surfaces, all 
the organs rupture, causing the condition which we have called "dropsy." 

Although the phenomena described here are related structurally, we 
have treated them separately because different conditions are the dominat- 
ing causes of different outbreaks. Many investigations have shown that an 
atmosphere heavily ladened with moisture is a decisive influence in causing 
intumescences. 

'J^eferences to my work and that of other older investigators may be 
found in the bibliography of Kiister's^ "Pathological Anatomy." I will cite 






'' 'WS^'/ 



Fit 



86. Cross-section throug-h the outer surface of 
pea-pods witli intumescences. (Orig-.) 



1 Kiister, Ernst, Pathologische Anatomic. Jena 1903. Gustav Fischer. 



448 

here a few especially pertinent observations. Some of these consider the 
question of light on the production of an intumescence. In this connection 
Atkinson^ explains that increased turgescence in leaves will be produced by 
repressed transpiration if the greenhouses are poorly lighted. Actually, in 
many cases, I found intumescences in the autumn and winter, because of 
cool, cloudy weather, if the greenhouses had to be heated after the plants had 
been brought in from outside. Trotter- states directly that half darkness 
favors the formation of intumescences. Steiner'^ also made the same 
observation, but stated that they will form only in the first days of darkness, 
so that one may conjecture an after eifect of the former activity of the light. 
This author observed also in Ruellia and Aphelandra, that the plants with 
equal atmospheric humidity only formed intumescences for a few weeks 
and therefore had adjusted themselves to the high degree of moisture. That 
the abrupt transition from dry to moist air is actually the decisive factor is 
shown by the renewed formation of intumescences, when the plants, after 
having become adjusted to a dry atmosphere for three weeks are brought 
again into moist air. 

Steiner found that no intumescences are produced under water, as did 
Kiister* on poplar leaves which he had left floating on water or nutrient 
solutions and in darkness as well as in light. Only when the illumination 
was too great, this process was suppressed, probably as a result of increased 
transpiration. In contrast to this, Viala and Pacottet^, in describing intu- 
mescences on grape leaves in greenhouses, said they had determined by 
direct experiment that intumescences are produced by the action of the 
light in a moist atmosphere. They are produced only directly under glass. 
The Missouri Botanical Garden makes a similar report. 

The most thorough experimental studies are Miss Dale's''. She ob- 
served with Hibiscus vitif alius, that the yellow and red rays are especially 
effective in producing intumescences. Her experiments with potatoes are 
especially instructive in regard to the action of sudden changes in the vege- 
tative conditions. The plants were grown in a cold section of a greenhouse 
and then set in a warm house at a temperature of about 2i°C., under a 
brightly illuminated bell-glass. After 48 hours, the stem and the upper 
side of almost all the leaves were covered with masses of pale green raised 
spots. If the plants were then brought into dry air, the blisters shrivelled 



1 Atkinson, G. F., Oedema of the tomato. Bull. Cornell AgTic. Exp. Station 
1893, No. 53. 

-' Trotter, A., Intumescences fogliari di Ipomea Batatas. Annali di Botanica 
1904, No. 1. 

•" Steiner, Rudolf, tjher Intumescenzen hei Ruelli formosa und Aphelandra 
Porteana. Ber. d. Deutsch. Bot. Ges. 1905, Vol. 23, p. 105. 

4 Kiister, E., tjber experimentell erzeugte intumescenzen. Ber. der Deutsch. 
Bot. Ges. 1903, Vol. 21, p. 452. 

^ Viala et Pacottet, Sur les verrues des feuilles de la vigne. Compt. rend. 
Acad. d. sciences 1904, No. 138. 

« Dale, E., Investigations on the abnormal outgrowths or intumescences on 
Hibiscus vitifolius. Phil. Trans. R. Soc. of London, ser. B. 1901, Vol. 194. — 
Dale, E., Further experiments and histological investigations on intumescences, 
with some observations on nuclear division in pathological tissues. Phil. Trans. 
R. Soc. of London 1906, ser. B. Vol. 198. 



449 

up to black spots or perforated the leaves. >If some leaves fell, when the 
the plants were kept longer under the moist conditions, a great cushion of 
intumescences was produced on the leaf scar which displayed similarity 
to the wound callus. Older plants under similar conditions did not 
develop intumescences as quickly, nor as abundantly, while very old leaves 
developed none. Pieces of leaves, laid in moist cotton, after possibly two 
days, were thickly covered with eruptions. Quickly growing plants react 
most easily to the stimulus of a sudden change in the amount of moisture. 

These observations support our theory that the formation of intumes- 
cences is the reaction of the organ to a stimulus due to a sudden increase 
of atmospheric moisture. Only the immature organ reacts. If older leaves, 
as we observed, for example, with Solanum Warsccwicsii, respond with a 
formation of intumescences after having been brought from the open air 
into a damp greenhouse, these are exceptional cases of a special excitability 
of the species. Such cases occur in various plant genera. 

My results differ from those of other investigators, since I always found 
that intumescences invariably developed as the result of an arrested assimi- 
lation due to an excess or deficiency of light. It always manifests itself, 
however, in the scanty formation of solid reserve substances, usually, in fact, 
those already formed become dissolved. In accord with Miss Dale's assump- 
tion, the variation in assimilation may be connected with the increase of the 
oxalic acid content in the cells showing in the abnormal increase in turgor. 
In the .same way, experiments with young leaves and pieces of leaves show 
how the root pressure may be eliminated. 

Different combinations of the vegetative factors may give rise to that 
deficient assimilation which shows itself in the formation of intumescences. 
In the greater number of cases falling under my observation, I find the cause 
to be an increase of heat and moisture given to a plant naturally dormant, 
or being forced to arrest its assimilation from external conditions. The 
following action throws light on inhibitory regulations. 

The Tubercle Disease of the Rubber Plant. 

On the under side of the leaves are found numerous abundant, very 
small, gland or tubercle-like, hemispherical swellings. These are produced 
by the pouch-like elongation (Fig. 87, int) of the cells of the leaf, which, 
in a normal condition, have the form and arrangement shown at the side of 
the picture marked m and, therefore, are separated by larger or smaller 
intercellular spaces (i). The morbidly elongated tissue (int) on the under 
side of the leaf thus approaches the normal leaf palisade parenchyma (p) 
which is provided with a three-fold epidermis (e). Of these three layers, 
the outermost is small-celled and provided with a very thick layer of cuticle. 
The innermost cell layer of the epidermis displays more thin-walled, com- 
paratively very broad cells (w), which form the so-called water-storage, 
protective layer. Isolated cells, enlarged like sacs, in this layer conceal 



450 

those peculiar grape-like clusters of cell substance incrusted with calcium (c) 
known as cystoliths. 

The close structure of the upper epidermis of the leaf must prevent the 
passage of air, while the lower epidermis is well fitted for this purpose. 
The spong}^ parenchyma shows large intercellular spaces (i), the enclosed 
air in which can pass out through the air chambers under the stomata (a) 
and the stomata (st) to the outside, making room for the freshly entering 
outer air. The conduction of water takes place through the leaf veins, one 
of wdiich is seen in section at (/ and shows at r the large ducts. The course 



7ZE/ 




Fig-. 87. Cro.ss-section through a leaf tubercle of the rubber tree- 



of organized building substances, produced in the leaf and flowing down 
toward the trunk, is shown at sch, the sheath of the vascular bundle ; k 
indicates the place at which the cells begin to enlarge because of an excess- 
ively increased turgor, thus filling the intercellular spaces and forming, 
therefore, first of all, "internal intnmescences." The excessive water con- 
tent manifests itself still more in the peripheral tissite, since, exposed only 
to the pressure of the epidermis, its cells elongate into tubes and, together 
with the epidermis, can be pushed outw'ard (int). 

Actually, therefore, the tubercle disease of the rubber plant is a regular 
intumescence which belongs to the previous division. We have, how^ever, 



451 



isolated this phenomenon of disease, becavise it has an essentially practical 
significance in the cultivation of Fiscus as a market plant. 

The disease occurs less often in plants grown for sale than in home 
ornamental plants, where it may lead to a premature defoliation. My experi- 
ments prove that it is produced by giving excessive heat and water to plants 
when their growth has stopped and their transpiration lessened, thus stimu- 
lating them to renewed activity. T produced intumescences by keeping a 
rubber plant in a very^ hot room and giving it abundant water after it had 
made a vigorous summer growth and passed into the normal resting period, 
instead of the cooler, drier environment which it should naturally have had. 
Leaves fell immediately, while intumescences were formed on the younger 
ones. When the plant was put in a light, but cooler place, the leaves with 
the intumescences remained on the stem until the next summer, when the 
plant again grew nor- 
mally if somewhat more 
weakly. 

This kind of disease 
and its cure may be 
considered characteris- 
tic. The intumescences, 
therefore, are highly shj- 
nificant synipfoms of ab- 
normal turgidity in all 
plants. As soon as they 
show themselves, the 
plant must be put into a 
light, cooler environ- 
ment and given a de- 
creased water supply. 




The Skin Diseases of 
Hyacinths. 



Fie-. 88. 



Hj'acinth bulb infected with the pustules of 
the skin disease- (Orig.) 



s scales which have lost their srloss. fi formation of pustles, 
r dried edpe. k young- bulb. 



This phenomenon 
(Fig. 88) has not been considered, although it occurs very frequently. 
Normally the outer scale leaves are smooth, firmly enclose the bulb, and 
usually extend up to its neck. In this disease they are short and die back 
from the dying edges. Often such hyacinth bulbs crack open and are 
thickly covered with dry leaves, especially near the place torn. On the still 
fleshy outer parts of the bulb, colonies of the blue-green mold (Penicillium 
glaucum) frequently occur. 

The leaves standing isolated, or connected with one another, are flat- 
tened on the upper side and often many boil-like, swollen, yellow places 
appear. In the colored part also of normally dried bulb scales, they almost 
always show some mycelium. In cultures this is proved to belong to 
Penicillium. The tissue of such diseased places differs from that of normal 



452 

scales in its yellow, uncommonly brittle walls, breaking into sharply pointed 
pieces and in the wide Kmiina of the cells, while that of the healthy ones, 
with their somewhat swollen, thick, colorless walls, have sunk together until 
the lumen disappears. All traces of starch have disai>peared from the 
yellow-walled tissue, which sometimes traverses the scale, is suberized, and 
pushed up by the subsequently produced cork cells and from the colorless 
surrounding tissue. 

After the diseased, dry bulb scales have been removed, one notices that 
the still perfectly white, succulent scales, normally extending to the neck of 
the bulb, have begun to dry, beginning at the top. Here the tissue loses its 
natural smoothness and turgor, so that gradually the scale has a folded 
appearance, due to the collapse of the cells which lie betw^een the more 
prominent vascular bundles. Besides this, the edge usually becomes yel- 
lowish. At the same time, on the deeper parts of the fleshy, white places in 
the scales, glistening from turgidity, appear small, longish, glassy, trans- 
parent, yellowish spots, protruding slightly above the upper surface. These 



Figr. 89. Cross-section through a scale of a hyacinth infected with skin disease. 

(Orig.) 

increase in a few days and almost at once become more noticeable because 
of the yellowish juicy edge. Then, however, the change advances more 
slowly, since the outpushing occurs only gradually more distinctly and its 
centre becomes whitish with a dr)^ membrane and longitudinal folds ; with 
increasing age, the centre becomes depressed and finally the scale seems 
perforated. WHien treated with sulfuric acid the upper lamellae, lying 
directly beneath the cuticle (Fig. 89 /) of the somewhat thickened epidermal 
cells, swell up markedly and at times mycelium may be found in them. 

A cross-section through the diseased scale (Fig. 89) shows at h an older 
pustule and on the left of this a younger one. In the discolored epidermis, 
the walls are swollen and this process of swelling and suberization (vk) in 
the older leaves has already advanced through the whole thickness of the 
scale. Here the fleshy, starchless parenchyma, which at the beginning {p) 
was found to be still colorless and with a normal arrangement, has col- 
lapsed like cords and' formed hardened places with irregular openings {s). 

In the cells directly beneath the outpushed epidermis, there are no nuclei, 
while they are present in the next inner cells, but brown in color. In the 
epidermis, cork cells are produced, while the parenchyma lying beneath gives 



453 

the sugar reaction with the Trommer test. In this tissue, rich in sugar, the 
formation of cork advances and since the corked cells do not collapse, they 
rise gradually more and more above the other tissue of the bulb scales, the 
walls of which retain their cellulose reaction and collapse. Analyses give 
dry substance 

Healthy bulbs. Diseased bulbs. 

In the outer scales 34.6 per cent. 51.82 per cent. 36.7 per cent. 55.43 per cent. 
In the inner scales 22.4 " 33-50 " 32.6 " 40.16 " 

Thus the diseased bulbs are richer in dry substance, which is not strange 
since the process of drvdng of the outermost scales has advanced rather 
further in them. 

After the removal of all the brown colored scales, the sugar content 
(defined as grape sugar and reckoned on dry substance) is, 

Healthy bulbs. Diseased bulbs. 

In the outer scales 0.71 per cent. 0.82 per cent. 

In the inner scales 1.23 " 1.66 " 

That is, the bulbs are richer in sugar in the inner, younger scales than 
in the older- ones, and when diseased both the inner and outer scales are 
richer in sugar than those in a healthy condition. 

We thus obtain the same results as were found in the ringing disease. 
As a matter of fact, both diseases frequently occur simultaneously and these 
pustules, which may be termed intumescences, prove to be symptoms of a 
scantier ripening of the bulbs. This may be found even in very luxuriantly 
cracked specimens. It is self evident that Penicillium grows rapidly and 
frequently on such a medium. The skin disease therefore deserves great 
consideration as a symptom and indicates that bulbs should be grown in a 
sandy soil not too rich in humus nor too damp. 

The Glassy Condttion of Cacti. 

A diseased condition was observed in various cacti and studied more 
closely by me with Ccreus nycticalus Lk. This condition is characterized by 
the appearance of glassy places, later becoming black. In the more delicate 
Cereus varieties, a greater extension of this tissue change kills the part of 
the stem which lies above it. Death results either through a drying up of the 
blackened tissue, or w^ith the assistance of bacteria, through the appear- 
ance of a pulpy condition, when the outer skin may be loosened by a slight 
pressure of the fingers. If the centre of disease is limited to one side of 
the stem, this may be healed, leaving deeper cup-like wounds. 

The illustration on page 456, of the manner of growth, shows a piece 
of the stem of Cereus nycticalus blackened at the upper end and softened 
to a pulp. On this softened part, a strip of the outer skin has been loosened 
by a slanting pressure of the finger. At the base of the piece of the stem 
are found healed wounds which extend to the wood ring of the stem. 



454 

When examining badly diseased specimens, it is noticed that a number 
of glassy places occur like warts on the upper surface. The cross-section 
shows that while the outer part of the bark of this piece of stem is still dark 
green and normally constructed, the underlying bark layers lack chlorophyll 
and starch and have greatly enlarged cells which cause the warty excres- 
cence. In contrast to the usual intumescences in which an elongation of the 
sub-epidermal layers causes the warty outgrowths which often rupture, I 
have termed the abnormal enlargement of the cell centres lying deeply 
depressed in the tissue, "internal intumescences." In this, these phe- 
nomena are related to the yellow-spotted condition described above. Here 
the first stages of the disease are found in centres of cells poor in content, 
browning and turning to cork in the midst of green tissue ; only in cacti the 
stems are afifected, while in Pandanus the changes are found in the leaf. 

The cell aggregations, which usually increase only in one direction, 
collapse, while, especially in the bark of the cactus, the cells retaining thin, 
colored walls, are usually elongated into tubes and have a star-like arrange- 
ment. From these inner diseased tissue centres, the process of impoverish- 
ment and over-elongation of the bark parenchyma extends backward toward 
the wood-ring and laterally in the direction of the bark, constantly further 
around until a considerable part of the stem is browned or blackened. 
Finally the outermost cell layers are also attacked by the discoloration 
without the usual appearance of any over-elongation ; rather, the stem 
appears as black as ink, even to the naked eye. 

In the first stages of this disease, wdiile the tissue still has a glassy appear- 
ance, the process of blackening occurs almost immediately after the sections 
are made, indicating that even then there are large amounts of tannic acid, 
which unite with the iron of the knife. Since, however, the discoloration 
follows when the plants have been injured with a horn knife, or with a 
platinum spatula, the presence of a sensitive substance must be assumed 
that rapidly discolors in the presence of the oxygen of the air. But 
guaiacum tinctures alone, or with hydrogen peroxide, do not give a blue 
coloration. With litmus paper the whole bark parenchyma gives a sharp 
acid reaction. 

An accumulation of glucose may be considered as a factor which might 
begin the over-elongation of the cells ; for, after treating the section with 
the Trommer sugar test, cuprous oxid is very freely precipitated in the 
glassy tissue as a whole, and this precipitate is scantier toward the healthy 
tissue. The proportion of starch content is the reverse. In the most dis- 
eased tissue, it is nil, while the healthier surrounding tissue displays starch 
abundantly. The proportion of calcium oxalate is peculiar; it occurs usually 
abundantly in the slime passages. In healthy green bark tissue, this calcium 
oxalate occurs chiefly as raphides, while in the diseased parts it is found 
usually in short octahedrons and at times in large cylinders. Probably 
varving amounts of the water of crvstalization determine the form. 



455 

The upiier figure in illustration 90 shows the process of heahng. It is 
a cross-section through the branch with a depressed wound, which may be 
seen at the base of the picture, showing the habit of growth. M is the pith 
with its shme cells ; H, normal old wood ; R, bark. It is seen at the wound 
that the tissue atrophy originally included the whole bark {R). The wood 
cylinder (//), however, was not attacked. The edges of the bark wounds 
{zvr) died and were separated by a full cork layer {t) from the healthy 
bark parenchyma at the sides. In the remaining part of the bark, a new 
growth in thickness had set in, which manifested itself by forming the 
primordia of new hard bast strands {b'). The old hard bast near the wound 
was diseased and found shut in by a cork envelope. 

The whole tissue zone (fe'-^')had been formed anew subsequently, and 
indeed in those parts covered by the bark by means of a normal cambial 
activity, but at the wound itself by an increase of the youngest sap wood. 
For the wound destroyed the cambium, and accordingly the last formed 
cambial wood layer has started a renewed increase of cells and has formed 
callus-like tissue. The primordia of the vessels, which at the time of the 
deposition of the latest sap-wood had already become thick-walled, have, 
however, not taken part in the increase, but have been pushed outward 
passively by the newly formed callus. It is seen in this, that these primordia 
of the vessels {g'), which in the cross-section resemble the ducts {g) in the 
normal wood {H), now occur isolated in the callus tissue. 

The healing process becomes more exactly recognizable in the lower 
anatomical figure which represents a piece of tissue from around the hole 
in the upper cross-section. H again represents the old wood with some 
vessels {g). Where the elements, represented with thick walls, cease, is 
seen the most depressed part of the wound. On this remain the youngest 
elements of the sap wood, which had increased in size and number after 
the phenomena of decay had ceased. The immature sap wood, already 
differentiated, became .more porous and thin walled, and thus it happens 
that thin- walled vessels {g') may be found again in a delicate parenchyma 
wood. All the tissue indicated by (w) has been newly formed, its produc- 
tion corresponding with the new formation of bark on peeled trunks. The 
new tissue, developed from the callus, already exhibits some differentiation. 
This diff'erentiation indicates that the stem is about to form new bark where 
it w^as injured, for in the region directly in front of the thin-walled vessels 
{g'), we find the first parallel cell divisions indicating the formation of a 
new cambial zone. Besides these, the primordia of secondary hard bast (&') 
may be recognized, to be sure, even in parenchymatous tissue with a plastic 
content but not containing chloroplasts, which later becomes normal bark. 

This healing process, however, has only been obser\'ed when the plant 
had direct sunshine and fresh air in circulation. I have learned to recognize 
the disease as occurring in greenhouses and indeed in those where because 
they contain plants from warmer climates the air is enclosed and very moist. 
In one special case, the abundant ventilation in the greenhouse stopped the 



457 

Fig. 90. At the right .side of the figure, indicating the manner of growth, is a 
reduced piece of tlie .stem of Cereus nycticalus, which, blackened and softened at 
the tip, .shows a piece of tlie barlv loosened by pressure of the fingers. On its lower 
part are found deep bowl-like wounds which have been healed- The upper drawing 
of the structure shows a. cross-section of a bowl-like wound which is being healed. 
The lower drawing gives the new structures and tissue differentiations, which take 
place during the process of healing the wounds. (Orig.) 

M pith, H wood, R bark, g normally placed ducts, £•' displaced ducts, b groups of dead, hard bast of 
the outer bark, enclo.sed by bark, d' groups of young hard Viast of the outer bark, 'cvr dead edge of the 
wound of the older bark (A*). The old tissue is separated from the healthy tissue by a layer of plate- 
like cork cells (/). ?i' and >i new bark differentiated from the wound callus, 

disease, while in the following year, with the new planting of foliage plants 
and with accordingly increased humidity in the air, it reappeared to a great 
degree. For this reason, I would like to consider the phenomenon as a 
direct result of excessive humidity. 

Methods for checking this are self evident. In one case, besides the 
increased supply of light and air, the addition of plaster to the soil has 
proved advantageous. 



We have devoted considerable space to intumescences and related 
phenomena in order to point to their importance. Greenhouse plants are 
chiefly considered and repeated observations have shown that most numer- 
ous diseases may be traced to the act that the natural dormant period of the 
plant was not considered and the plants were stimulated to untimely and 
therefore abnormal growth, by a high degree of heat and moisture. 



CHAPTER VI. 



Fog. 

In temperate climates, complaint is rarely heard of injuries from fog. 
In the mountains, vegetation has adjusted itself to the abundant precipi- 
tation and the attempt has been made so far as possible to overcome the 
delay of ripening grains and of drying the remaining vegetable produce by 
cultural regulations. 

The so-called "fog holes" of the plains may also be "frost holes." 
These are distinguished by a vigorous lichen growth on the tree trunks. 

In warm regions, fog becomes a more important factor, causing damage 
to plants, since it actually favors the development of saprophytic and 
parasitic fungi. We find the greatest number of complaints in regions 
where cotton is grown and exhaustive descriptions have been sent from 
Egypt. David^ writes from the cotton experiment station at Zagazig that 
each October morning in lower Egypt, the soil is covered by heavy, thick 
vapors or low fogs. The first general result is that the bolls do not open 
because the carpophyles remain too tough. The foliage becomes covered 
with red spots, ascribed to the action of the sun on the dew drops, acting as 
lenses. The cotton fibres in the bolls decay and lose their value from the 
action of a black fungus. Besides cotton. Hibiscus esculantus and H. 
cannabinus also suffer; young maize plants as well. The irrigation with 
Nile water, its soaking through the land while the soil is fallow, makes it 
moist, dense and slimy or oozy. This physical characteristic is the chief 
factor which makes Egyptian fogs more disastrous than the English and 
mountain fogs. 

The sensitiveness of cotton is due to its special soil and climate needs. 
These are very thoroughly described in Oppel's'- special work. According 
to this, cotton as a low-land plant cannot endure a stony soil or any abrupt 
changes in temperature. In its time of growth, lasting six months, it 
requires i8° to 20°C. a medium heat and abundant moisture, but it is found 
to be very sensitive to continued rain. "A high degree of atmospheric 
warmth, a good deal of soil warmth, a clear sky during the day and abundant 



1 David, Nebel und Erdausdiinstungen und ihr Einfluss auf agyptische Baum- 
wolle. Zeitschr. f. Pflanzenkrankh. 1897, p. 143. 

' Oppel, Die Baumwolle nach Geschichte, Anbau, etc. Leipzig, cit. Bot 
Jahresber. 1902, I, p. 374. 



459 

dew at night are the chief conditions." After the blossoms open, dry 
warm weather must prevail. Sandy soil is especially suitable. In soils 
rich in humus the plant runs to foliage. Clay soil is absolutely unsuitable, 
since it does not let the water percolate through. 

However, examples of adaptation to the climate are known. Thus, 
Webber and Bessey^ report that cotton, when carried from the Bahamas to 
Georgia, did not thrive at first, but gradually adjusted itself to the temper- 
ate climate. 

However, fogs, even of the English variety, may become disastrous, 
especially near cities with many factories. P. W. Oliver-, upon the re- 
quest of the Royal Horticultural Society, has published the most extensive 
studies on London fog. The most troublesome admixture is the smoke, 
the elements of which coat not only the plants but window panes, etc., with 
a sooty covering. An analysis of this sooty covering shows : 

carbon 39-00 per cent. 

hydrocarbons 12.30 

organic bases 2.00 

sulfuric acid 4-33 

hydrochloric acid 1.43 

ammonia 1.37 

Metallic iron and magnetic oxid 2.63 

Silicate, iron oxide and other mineral substances. 31.24 

The injuries to plants are usually only phenomena of discoloration. 
However, different plants are more susceptible ; hence the fog may cause 
the dropping of the leaves. In injuries of the first kind, leaf tips and edges 
become brown, but the remaining leaf surface is still capable of functioning 
(Pteris, Odontoglossus, etc.). The dropping of leaves with yellowing and 
browning, or even without any external signs of injury, is the most frequent 
result. Sulfuric acid is considered as the cause of the leaf destruction; in 
addition, Oliver ascribes as an injurious influence also metallic iron. In 
deciduous plants which remove all the starch from the leaves before they 
fall, the most important agent exciting abnormal leaf fall is sulfuric acid. 
PLxperiments determining a rapidly reduced transpiration show reactions 
similar to these from fog, if at the same time the light was decreased. I 
also ascribe the emptying of the cells to the lack of light, for with the action 
of the acid alone, I found in my experiments that the whole cell contents 
died quickly and were deposited on the wall. 

Of the tar compounds, pyridine was found in fog in especially large 
amounts. When exposed to vapors of this substance, the leaves became 
limp and a darker green. The cells were plasmolyzed; the cyptoplasm in 
the epidermis had turned brown, but the chlorophyll did not change. As a 



• 1 Yearljook of the Dept. of Agriculture, 1899, p. 463. 
2 Oliver, F. W., On the effects of urban fog- upon cultivated plants. Journ. 
Hortic. Soc. Vol. 16, 1893; cit. Zeitschr. f. Pflanzenkrankh. 1893, p. 224, und Gard. 
Chron. 12, 1892, p. 21, 594, 648, etc. 



460 

rule, wherever a brown coloration occurred, tannin was found in the cells. 
The penetration of pyridine, like that of sulfuric acid, takes place chiefly 
through the stomata. Very similar effects were found also, due to sub- 
stances related to pyridine, such as picoline, lutidine, nicotine, thiophene, etc. 

Phenol attacks the foliage very vigorously in aqueous solution as also 
in the form of vapor, with strong plasmolysis and a brown 'coloration of the 
protoplasm and chloroplasts. 

The blossoms behaved very differently in relation to fog; at times they 
showed considerable difference in two varieties of the genus and, in fact, in 
different petals of the same blossoms. Tulips, hyacinths and narcissus were 
very resistant. 

It is interesting that, as a result of the lack of light connected with the 
fog, whereby assimilation, transpiration and respiration are repressed, a 
peculiar yellow-spotted condition often sets in. In this, there is an accumu- 
lation of the acid content (because, with the decreased respiration, less 
organic acids are burned) and an increase of turgescence connected with 
this seems to lead to cell elongation in the mesophyll (aurigo). 

Thus, in considering the eft"ect of fogs, we have to consider two injuri- 
ous factors, the decreased light and the action of the poisonous substances. 
This becomes the more dangerous the greater the plant's need of light. 
Plants adjusted to a lesser supply of light (ferns) are less sensitive. 

Only in greenhouses can the injurious effect of such fogs be lessened, 
and this has been done in England. Special purifying apparatus is made 
use of (fog annihilators), with which the air entering the greenhouse is 
passed over strongly absorbing substances (charcoal). For out of door 
planting only a choice of resistant species can come under consideration. 



CHAPTER VII. 



RAINSTORMS. 

The injurious effects of beating rains on the soil have already been 
mentioned. They pound the upper surface down or cover it with great 
quantities of silt. The immediate result is oxygen starvation for the roots. 
The mechanical effect of heavy rains on the plant itself is first to be con- 
sidered. There are many natural devices in plants which safeguard the 
leaves from the beating and tearing effects of heavy rains or the undue 
accumulation of water from long continued gentle rains. StahP and 
Jungner- have given a thorough presentation of these conditions and call 
attention to the formation of the tips and to the position and repeated 
division of the leaf surface, etc. 

The direct results of the rain are a decrease of transpiration and a great 
water absorption by the roots. They have been less considered. Here also 
the swelling of the wood of trees belongs. Fried rich's investigations^ show 
that a constant swelling of the tree trunk (aside from any direct growth) 
takes place during the night because with lessened transpiration, the tree 
swells, while in the daytime it shrinks. The differences will be most marked 
when the growth is rapid and the wood swells, especially when rain comes 
after considerable drought. Bark and periderm are less affected. Growth 
and swelling of the wood cylinder are regulated by the influence of atmos- 
pheric humidity on the tops of the trees. 

It is thus easily evident that smooth bark will crack in places because 
of the strong and sudden increase in swelling and growth. When the soil 
is rich and the atmospheric humidity great, these cracks may become open 
w^ounds. constantly increasing by bacterial infection. Rough places then 
arise on the bark of the young tree trunks. These may be observed, for 
example, in lindens, elms, ashes, maples, etc., near wet ditches and ponds. 

The influence of longer periods of rain manifests itself in herbaceous 
plants, even more than in woody ones, by cracks in fruit and stems. Among 



1 Stahl, B., Regenfall und Blattgestalt. Ein Beitrag- zur Pflanzenbiologie. 
Annal. de Buitenzorg.; cit. Bot. Jahresber. 1893, 1, p. 49. 

- Jungner, J. R., Om regnblad, daggblad och snoblad. Bot. Not.; cit. Botan. 
Jahresber. 1893, p. 49. 

^ Freidrich, Josef, tJber den Einfluss der Witterung auf den Baumzuwachs. 
Mitteil. iib. d. forstl. Versuchswesen Osterreichs. Wein 1897, Part 22. 



462 

our vegetative plants, the splitting of cucumbers is most important. The 
fruit suffered most of all, but sometimes the stems also cracked. Decreased 
temperature, accompanied by continued rain, not infrequently causes the 
total failure of harvests, since the cucumbers often show gummosis and are 
attacked by various black fungi. 

Long, cool rainy periods also cause a premature leaf fall, badly devel- 
oped heads in grain, a small amount of sugar and starch in beets, tubers, etc. 

Repeated showers have a very disastrous effect when they fall on 
blossoming fruit trees and during the setting of the seeds of field crops. In 
the first place, the insects, necessary for fertilization, cannot fly about so 
freely, and secondly, the anthers will not open so well, nor will the pollen 
grains stick so well on the stigma. 

Nevertheless, the theory that the increase of bacteria and fungi is 
always favored by periods of rain does not hold absolutely. Parasitic 
diseases usually increase only if the rain is accompanied by warmth. On 
the other hand, cold wet weather retards the growth of the most important 
parasites (rusts, false mildew, etc.). 

In tropical regions, however, rain storms usually favor the development 
of fungous diseases and, to give at least one example, we will mention 
Busse's obser\'ations\ He found that the Phytophthora decay on the cocoa 
fruits was especialy marked in rainy years. The amount of rain is not 
decisive but rather the character of the storm. Mighty gusts of rain seem 
to keep the fungus spores from settling on the smooth-shelled fruit ; but the 
softer, more frequent rains, easily producing stagnant moisture in the de- 
pressions in the soil and in the regions where the drainage is poor, have 
proved favorable for the fungi. Those regions suffer less to which the fresh 
sea breezes or some wind has unhindered access. 

Among cultivated plants in rainy seasons, the wind is a helpful agent 
in the struggle against parasites. This helpful agent has never been suffi- 
ciently credited for its work. The tops of trees should be freed of excessive 
water by frequent shaking. This should be done especially in closely planted 
orchards and in warm rainy periods. 



1 Busse, W., Reisebericht der pflanzenpatholog^ischen Expedition d. kolonial- 
wirtschaftl. Komitees nach Westafrika. Tropenpflanzer 1905, p. 25. 



CHAPTER VIII. 



HAIL. 



All injuries from hail form wounds, with a consequent loss of sub- 
stance ; any chemical action as a result of the cold of the hailstones cannot 
be demonstrated ; only the mechanical blow which either tears away various 
parts of the tissue and, by drying, causes them to go to pieces, or slits the 
leaves and branches in knocking ofif more or less large pieces. 

The small piece of rye-blade, which is shown here, has been struck by 
hail at the points g, c and v, and shows the effects of the blows of the hail 
stones. In considering such a section after a hail storm which has not been 
severe enough to knock ofif the leaves, or heads, or to break the whole stalk, 
we find, as every' one knows, whitish or white spots on the green striped 
upper surface. The striping is produced by alternate dark green furrows 
and lighter colored lines. In cross-section, it is seen that these furrows 
consist of a soft bark parenchyma, containing chloroph)dl, while the lighter 
colored stripes are composed of thick-walled fibre-like cells (/>). These 
fibre strands stiffen the blade. The thicker their walls are, the more re- 
sistant the blade is and the less inclined to fall. In Fig. 91, the green 
parts are seen to be changed most. The cells at g appear uninjured; at 2 
only dry cell walls are found, which are connected with one another by a 
scaiTolding-like structure. Toward the centre of the blade, however, there 
is green living tissue (m). Here, the blow of the hailstone has not destroyed 
the epidermis (^) at all,, but has bruised the more delicate bark parenchyma 
underlying it so that part of the cells have died. Only a few pieces of the 
cell walls of the former juicy bark tissue remain and, at this point the hail- 
stone has had such force that it has broken the thick-walled, tough epidermis 
at 0. Air has entered through this opening and this hail spot appears white 
to the naked eye, while at m a greenish tone may still be noticed. 

Similarly, the loss of tissue will take place in other parenchymatous 
parts of the plant and the assimilatory activity will fall according to the 
severity of this loss. Yet, this reduction of the life-activity may become of 
great influence only if the hail storm sets in at a time when vegetative 
growth has stopped and the plant has entered upon the reproductive period, 
when it withdraws the cytoplastic substance from the leaves. 



464 

C. Kraus' made his observations on barley and describes the effect of 
hail storms on the grain. He found many heads greatly bent backward and 
turned, since, after the buds had been hit by hailstones, they were so bruised 
that only the furthcrest developed could free their tips from the outermost 
leaf sheathing. ' Heads which had been hit directly were retarded in their 
whole development ; the kernels were lighter, not uniform and often tipped 
with black. The v.eight of the heads was about 38 per cent, of the normal, 
that of the grains about 43 per cent. Kraus found similar conditions in 
two unbearded wheats, in which, however, because of the absence of beards, 
the heads had worked their way more easily out of the uppermost leaf sheath. 
Accordingly the weight of heads of wheat struck by hail was only about 




Fig. 91. The effect of hail on a blade of rye. (Orig.) 

g healthy green tissue, z tissue injured by a hail-stone, ii adjoining healthy tissue, v completely 

destroyed bark of the blade with ruptured outer membrane (a), h parenchyma of the blade, b 

vascular buadle, p ropes of cells resembling bast fibres. 



24 and 15 per cent, and the weight of the grains about 27 and 17 per cent, 
less than normal. 

When the hail storm occurs early in the year, i. e., perhaps in May, 
many shorter green glades bent at the base are found later between the 
ripening, upright ones covered with hail spots. The hailstone had probabl}' 
bent the plant and the blade required more time to straighten and this had 
delayed ripening. 

Wheat seems to be the most robust. I observed after a hail storm in 
June, 1905, that rye blades showed the injuries represented in Fig. 91, while 
in the corresponding cell groups of the wheat, the inner tissue was split by 



1 Kraus, C, Wirkunj 
1899, Nos. 14-15. 



von Hagelschlagen. Deutsche Landwirtschaftl.Presse 



465 



only one tear or was not injured. The epidermis was not torn, but only the 
walls and contents were browned. 

The heads were broken in a very charac- 
teristic way. Fig. 92 shows a slight breaking, 
with the axis making an obtuse angle (A). In 
the more severely injured heads, the axis was 
bent two or three times, and where bent was 
almost bare. 

Fig. 93 shows the construction of the axis 
where bent : g, ducts ; r, torn parenchyma ; "<', 
a vascular bundle, which has been killed. 
Laterally from this, at br, the tissue as a whole 
was a deep brown. Where other heads had 
been hit the epidermis was torn open ; the 
bordering tissue had collapsed, fallen to .pieces 
and turned brown. Some vascular bundles 
were found to be almost entirely isolated, since 
the torn or disintegrated parenchyma had 
cracked off. This might be a result of ten- 
sion, since later the still green heads continued 
their growth. The injuries vary very greatly 
according to the way the hailstones strike. 
Kraus's observation shows that after the hail- 
stone had struck the head before it had become 
rid of the leaf sheath, the beards remained 
where they were. Therefore, the head ap- 
peared bent like a bow. The injuries usually 
\\'cre at the points where the young heads are 
attached rather than in the internodes of the 
axes. 

Oats will endure severe injuries if the 
panicles are still enclosed in the upper leaf 
sheath when the hail storm strikes them. F'er- 
fectly sterile heads may be produced and the 
injury to the plants resembles that of thrip so 
much as to lead to confusion. In some years 
I have often found twisted barley heads due 
to the sucking of thrip. PuppeF has often 
studied tlie effect of mechanical blows and his 
illustrations are very helpful. For example, 
with a heavy smooth roller, he flattened a field 
of young winter rye which had not yet formed 
a blade. When the heads began to develop, 
they were deformed exactly as if they had been injured by hail. 

1 Puppel, Max, Hagel- und Insektenschaden. 40 plates from original photographs. 




Fig. 92. Head of wheat broken 

by hail. The grains have fallen 

at the broken place, leaving it 

bare. (Orig.) 



466 

Wheat, hit by hail on the 4th of June, was pecuHaiiy injured. Besides 
the well known hail wounds, plants were found scattered throughout the 
field with a green appearance and almost empty heads. In July, the kernels 
present were still green and milky. The heads, as a whole appeared a light 
leather-brown, due to the discoloring of almost all the glumes. Among 
these were found short, fresh green tips which belonged to the sprouted 
small heads. These contained six to eight blossom primordia, not one of 
which had developed, and the uppermost showed only the beginnings of the 
anthers. The glumes were lancet-like, dark green and as soft as any 
herbaceous growth, so that a distinct transition to a foliage character was 
recognizable. In one case young plants had actually sprouted out of the 
base of some small heads. 

Behrens^ obsen-ed similar conditions in hops after a hail storm occur- 
ring on the first of July. Four weeks later the blossoming catkins opened 




Fig. 



93. Cross-section through the stalk of the wheat head of the previous figure, 
at the place broken by hail (h). (Orig) 



and contained only leaflets. The author's experiments connect this trans- 
formation of the inflorescence actually with the destruction of the leaves 
by hail. On vines from which the leaves had been stripped, the so-called 
brausche hops grew (see p. 344), while on the stems on the same place 
which had not been stripped, catkins developed normally. 

In potatoes, it has been observed that injuries due to hail reduce the 
starch content of the tubers^ Injury to the pods may seriously affect rape. 
It is a matter of course that, in all cultivated herbaceous plants, the destruc- 
tion of the leaf must affect the yield — even to the loss of the harvest. It 
would he a mistake to remove foliage injured by hail. Experiments with 
cabbage plants showed that better heads were obtained when the injured 
foliage had been left than when it had been removed. 

1 Zeitschr. f. Pflanzenkrankh. 1896, p. 111. 

2 Jahresber. d. Sonderausschusses f. Pflanschutz 1903, p. 94. 



467 



Internal injuries in juicy fruits, caused by hail, are interesting. Fig. 
94 shows a cross-section of a tomato fruit skin struck by hail. We notice 
at the left, the actual place hit, a hard, dry dark-brown excrescence, 
the blow of the hailstone did not destroy the epidermis (e). The more 
tender sub-epidermal tissue was fatally bruised and consequently turned 
brown and dried (t). As a result of the further process of swelling, the 
tissue of the still unripe fruit is torn and transformed to a hard cyst. 

Besides this injury, which is most strikingly noticeable, however, a 
second hard place is found in the juicy flesh of the fruit surrounding a 
vascular bundle (</). The hardness of the tissue arises here because of 




Fig. 94. Cross-section througli tlie fruit wall of a tomato struck by liail. (Orig.) 

<? epidermis of the outside of the fruit, r' epidermis of the inside of the fnut wall, -c dead edge of the wound 
cut off from the livinjir tissue by plate cork (/), r cells elongated radially and in part forming: dividing walls, 
III normal cells of the fruit flesh./ the beginning of the formation of plate cork, g va.scular bundle. /; vas- 
cular bundle sheath, ir division of the cells which are over-elongated radially to form a va.scular bundle. 
X- zone of cork tissue, .v/ starch, - collapsed cells with swollen cork walls. 



suberization, which has afifected the whole spot after the cells had begun to 
elongate and divide freely in the vicinity of the bundles. This has probably 
been initiated by the change in a ring-like zone {2) at a definite distance 
from the vascular bundle due to the blow from the hailstone or its after 
effect. Some of the cells have collapsed from the swelling and suberization 
of the walls ; in other cells, the walls have only swelled, while the walls of 
the adjacent cells have only been suberized. When the hail fell, the fruit 
was still green and rich in starch and, during suberization, the starch was 
retained in the irritated tissue zone, while, during the ripening, it has disap- 
peared from the rest of the fruit flesh. On this account, we see a ring 
drawn about the vascular bundle, composed of deep brown tissue filled with 
starch (st). 



468 

Because these cells die and partially collapse, they make possible the 
elongation of the cells lying directly about the vascular bundle and rich in 
water. They have elongated in an approximately radial direction, begin- 
ning at the sheath of the vascular bundle (h) and have divided by parallel 
cross-walls (w). Besides the actual place of injury, the parenchyma of 
the fruit wall has also participated in the radial elongation (r) and only 
the inner flesh remains normal. On the boundary between the normal and 
the over-elongated tissue a formation of flat cork (/) began at the time of 
the observation. Joining the corked internal spot, this forms a consistent 
tough mass. 

Similar cork places are met with in pomes, such as apples. Here, too, 
the blow from hail often causes no open wounds, especially in unripe fruit. 
We find only depressed places, which later turn practically brown. The 
depression is produced by the bruising of the parenchyma of the apple skin, 
lying under the epidermis which has not been injured, and, as a result of 
which, it has dried and split, usually in radial cracks. Here, as in the 
tomato, the starch has been retained in the corked tissue, adjacent to the 
hail wound, in case the apple was still green when struck by the hail. In 
this case, irregular zones of cork cells in the form, of an hour glass are 
often developed later, which cut ofif the whole internal hail wound from the 
healthy flesh of the fruit. 

Most significant are the bark injuries due to hail, which, in themselves, 
as a rule, are of sUght extent, but represent considerable damage because 
of their frequency. So far as I have had opportunity of observing these 
injuries in fruit trees, I have found that the disturbance in the tissue has 
not been confined simply to the bruised place but has also spread laterally. 
In hail wounds on the one year old twigs of the current year, on which they 
cause relatively the most considerable injury, the disturbance spreads later- 
ally from the actual place of injury in the form of a softening of the bark. 
As a result of this we see, in cross-section, stripes of parenchyma extending 
from the dead zone outward, and usually filled with starch, pushing into 
the normal wood and softening it. It thus acquires brittle and crumbly 
properties, which may be of special importance in those trees whose twigs 
are used as tying and braiding materials (willows and birch). Wounds, due 
to hail, may often be distinguished from the injuries due to frost by their 
position in the annual ring. Since hail usually occurs in the hot season, the 
wounds lie near the end of the annual ring, while frost injuries appear in 
the spring wood. It is striking that beneath the places hit by hail in the 
twig of the current year's growth, upon which frost cannot have acted at 
all, one finds at times in the radius of the wounded place, that the pith is 
browned and the spiral vessels greatly discolored, since the wood of the 
vascular bundle, lying between the injury and the pith crown, is healthy. 
The only possible conclusion is that the disturbance extends back toward 
the pitli through the medullary rays. 



469 

Often hail wounds may be distinguished from frost wounds because 
straight lined normal wood, with numerous vessels, very soon appears again, 
while, when the frost cracks heal, broad zones of parenchymatous wood 
may be found, due to the great extension of the adjacent edges. When the 
hail injury is slight, the bark is not uniformly destroyed, and the cambium 
continues growing with many gaps. 

When bark has been injured it peels at this point very unevenly and 
unsatisfactorily from the wood. This has an economic effect, since, when 
oak is grown for the commercial use of the bark, the shoots, struck by hail, 
peel very*unsatisfactorily. 

Often hail wounds provide openings for other diseases. If wet weather 
prevails for some time after the hail storm, decomposition frequently sets 
in, due to attacks of fungi, etc. In the Amygdalaceae an exudation of gum 
may set in. Such secondary diseases may later destroy the branches. If 
this dying back extends to the top shoots of young trees, deformed tops or, 
in seedlings, crippled trunks are of frequent occurrence. 

In fruit nurseries, after a severe hail storm which has greatly injured 
the smooth barked trunks, these trunks should be pruned back almost to the 
bud, thus renewing the stem. When the tops of older trees have been badly 
broken and deformed by hailstones, it is advisable to try to reform the top 
by severe pruning in the following spring. Ordinarily, the power of regen- 
eration is so great in trees that hail wounds heal over easily, but when large 
pieces have been torn from smooth barked trees by the incessant beating of 
hailstones, it will be necessary to hasten the closing of the wound by using 
some tree salve. When the roughened surfaces of the hail bruise have been 
made smooth by cutting with a sharp knife, they will heal more easily. 
Then a mixture of loam and cow-manure, free from straw, with ashes or 
powdered slate kneaded into the form of a salve, should be used. 

With the present mania of wishing to cure everything by manuring the 
soil, it is not surprising that, even in extensive injuries, as from storms and 
hail, with a loss of substance, fertilizers will be applied at once. We would 
caution against the use of this ; even on poor soil, fertilizers should be used 
only when the tree has already made new growth. Large wounds which 
will take some time for healing, are best closed by painting with tree-wax, 
which flows when cold, i. e., with a mixture of resin, which thus prevents 
the entrance of water. It is cheaper to coat the wound with coal tar. 

In connection with fruit trees and grapevines, Miiller-Thurgau empha- 
sizes our warning in regard to retaining the foliage in vegetative plants 
which has been injured by hail\ 

In growing grapes, a certain hard flavor is mentioned". This is sup- 
posedly the result of a fungous infection of the places when hail has injured 
the grapes. These grapes should be cut out, though the work is very tire- 



1 Miiller-Thurgau, Beobachtungen iJber Hagelschaden an Obstbaumen unci 
Reben. VII. Jahresber. d. ^''ersuchsslation zu Wadensweil. 

2 Chronique agricole du Canton de Vaud vom 10 Augu.st, 1895. 



470 

some. The broken cluster closes again completely as the grapes left grow so 
much the larger. If the injured vine is to be pruned, this should be begun, 
at the earliest, a week after the hail storm in order to see how far the plants 
have recovered. In pruning, as much growth of the current year as possible 
should be left. It is especially important not to force prematurely lower 
eyes which promise fruit. By using precaution^ at least twice as many eyes 
are left on the vine above the real fruiting eyes as are needed in the follow- 
ing year. 

The method of spreading nets of galvanized iron wire over the vines, 
said to be customary in Piedmont, should be recommended for further test- 
ing, as a means of protecting the vines from injury-. 

Recently many experiments have been tried with "cannonading against 
hail." Nolibois^ developed the theory of this method. The water vapors 
arising from the soil are condensed into clouds, the moist dense layers lying 
lowest. When these lower layers are greatly condensed by the radiation of 
the soil, the layers directly above them are cooled greatly, occasionally below 
zero. Any shock is now sufficient to bring the overcooled mist to freezing 
and precipitation. If the process is continued, there is a constant w^eakening 
of the cold action in the upper cloud layers, resulting finally in rain. 

According to this theory, declivities would be more exposed to hail than 
lowlands ; lime or sandy soil more than moist alluvial soil ; bare soil more 
than forests; land more than lakes or the ocean. If superimposed cloud 
layers could mingle one with another so that the temperature is more equal- 
ized, and over-cooling hindered, the formation of hail might be prevented. 
Attempts are now being made to produce such movement of the layers of 
the air adjacent to the clouds, by the explosion of cannon. 

Another theory based on the production of whirlwinds resulting from 
the mingling of cold air from the mountain with the hot, rising stream of 
the valley*, likewise recommends cannonading against hail. In Italy numer- 
ous shooting stations have already been formed, yet the reports are very 
contradictory. . More favorable reports on the cannonading of the air have 
been sent from France^. 



1 Ungarische Weinzeitung- 1896, No. 34. 

2 Rho, G., Le reti metalliche a difesa delle viti dalla g-ragnuola. Bollet. d. 
Soc. dei Viticoltori. Roma 1892; cit. Zeitschr. f. Pflanzenkrankh. 1894, p. 168. 

3 Nolibois, P., Theorie de la formation de la grele; cit. Hollrungs Jahresber. 
f. Pflanzenkrankh. 1904, p. 73. 

4 Bordiga, O., Grandine e sari. Atti del R. Istituto d'incorraggiamento, Napoli, 
Vol. II, 5 Ser. 

5 Praktische Blatter f. Pflanzenschutz, herausg. von Hiltner, 1905, No. 11. 



CHAPTER IX. 



WIND. 



Among the sudden efifects of severe wind are the injuries known as 
"uprooting of trees by wind" and "breaking of tree trunks by wind." In 
the first, the trunks of the trees are thrown over to one side, taking the root 
systems with them. In the second, which is economically more injurious, 
the trunk is broken ofif. 

The action of the storm depends upon the variety of the trees, the 
stiffness of the individual trunk and its location. In regard to the variety, 
it may be remarked that tough wooded genera, like birch, spruce, hornbean 
and redbeech are more often overthrown than broken. Pines and oaks 
break more easily. The kind of 'break also differs with the genus. It 
seems as if pines break off shorter, while the oak splinters and the brittle 
acacia often shows deep clefts on the stump, extending downward from the 
broken surface. In regard to the individual firmness of the trunk in the 
same variety, it is evident that trees, rotten at the core, break most easily. 
The individual structure of the tree top, which forms the chief point attacked 
in the lever represented by the trunk, is likewise of importance. The 
position and the local conditions influencing the structure of the root system, 
essentially under consideration here, are of the most extensive influence. In 
deep soil, those trees will endure more wind which have not been trans- 
planted, since in transplanting the tap root has been cut off to make the 
moving easier. In shallow soil, the advantage of the tap root is lost and 
the development of the top becomes the important factor. The higher the 
branching begins on the otherwise smooth trunk, the higher is the centre of 
gravity, and the more liable the tree is to be uprooted or broken. Pyra- 
midal crowns are therefore prob?bly better than those of a dense spherical 
form. There are naturally exceptions to the rule; the more exposed the 
location of the tree, the greater the danger of injury. On mountain slopes 
it is often noticed that injury due to storms, especially in uprooting the 
trees, is far less extensive on the windy side than on slopes on which the 
storm passes downward. Further, whole groups will be overthrown often 
in the centre of an uniformly old tract of trees. This may be explained by 
the fact that the wind, in blowing upward, is more uneven and can effect 
only a small part of the crown of one tree because another standing lower 



47^ 

down on the declivity is directly in front of it. This rising of the tree tops 
in tiers can often be perceived in forested level costal regions. Only, here 
the terracing of the tree tops is not produced by inequalities of the soil and 
trunks equally tall, but by a different height of the trunks, on level soil. It 
is noticed that where coast winds strike the trees, the outer trees do not 
grow tall, but are kept down like shrubs. Only at some distance behind 
these, and increasing with the distance, do they grow to the height of forest 
trees. Whirlwinds will overthrow whole groups of trees in the centre of 
an uniform tract. A different natural form of wind protection is men- 
tioned by Schiibeler^ (see p. 253) for spruce families, from the Gudbrands- 
dal, at an elevation above sea-level where the spruces approach their height 
limit. The trees are usually arranged in rows in exposed places, and in fact 
in such a way that the main trunk stands at the side turned toward the pre- 
vailing wind, while the branch suckers form a pretty straight line behind the 
parent tree. Therefore, only where this parent tree keeps off the wind is it 
possible for the young sucker trees to grow up. 

In the tropics the cultivation of cocoa is often affected by the wind 
storms. Aside from the indirect losses from overthrown shading trees, the 
wind also directly tears apart the forkings of the main branches. Accord- 
ing to L. Kindt's reports, an attempt has been made to produce tall tree 
trunks from the remains of the bush forms, injured by the wind, by letting 
one of the many water sprouts grow up and then forcing it, by topping, to 
form branches. This process has been found partially advantageous, but 
has been entirely abandoned by Kindt upon his own experience. He found 
that in such an artificial formation of the trunks, contrary to the nature of 
the tree, only scanty, weakly leaved crowns formed of short horizontal 
branches are produced in which fruits, ripening prematurely, are found only 
on the trunks. The yield is not satisfactory quantitatively and qualitatively, 
not only in the first year, but also in subsequent years. 

The duration and time of the storm, as well as the prevailing weather, 
should be taken into consideration. In rainy periods, the softened soil 
gives way more easily and predisposes toward the uprooting of trees by 
wind (see Sewage Fields), while a spring storm on frozen soil finds the 
trees more firmly anchored and, with increasing strength, causes more 
windbreaks. 

Aside from these gross injuries occurring at once, however, those 
should also be recorded which do not destroy the existence of the individual 
but only weaken it temporarily or permanently. 

Among wind damages belongs an inclined position of the trunks. The 
most striking and frequent phenomena are offered by street trees, especially 
where gutters run along both sides of the avenue or highway. The striking 
discovery may be made here, that if the street runs perpendicularly to the 
prevailing direction of the wind (with us usually a west wind), the most 
exposed rows of trees have comparatively erect trunks, while those on the 



1 Schiibeler, Die Pflanzenwelt Norwegens. Christiania 1873-75, p. 163. 



other side are more or less bent, overhanging the gutter and often exhibiting 
a curved growth. The inequaHty of the root support is evident from this. 
On the windy side of such a street, where the wind first strikes the surface 
of the gutter, the root system has developed differently; on this side, the 
roots cannot extend as far but are strongly fastened within the street dam. 
The wind pressure finds in this support a sufficiently strong counterbalance ; 
on the other side of the street, the conditions are reversed ; here, to be sure, 




Fig. on. Two wind bent and broken spruces; the tree on the left has two witches' 
bi-ooms and three secondary tips. (After Klein.) 



the roots are better developed in the street itself, than on the side toward the 
gutter, and form the anchoring apparatus which counteracts the strain of 
the bending trunk. The propping side of the roots lies toward the gutter 
and, being weakly developed, causes the tree to incline toward this direction. 
It seems, therefore, that the tap root planted at an angle against the direction 
of the wind will form the most effective protection of fruit trees. Guy wires 
attached on the windward side are more commonly used, and serve also to 
relieve the strain of the tree, but may well be considered less useful. 



474 

This "sabre" or curved growth is explained by the annual bending by 
the wind when the shoots are forming in the spring and summer. The tip of 
the trunk, continuing its growth at this time, tends always to maintain the 
perpendicular position and bends only as the tree is quickly blown toward 
the horizontal. All that has been said here, in reference to the main axis, 
refers also to all branches which, in windy positions, actually produce a 
one-sided, flag-like top. 

The flag-like character results from branches bending away from the 
wmd (with us toward the east) and from the scanty branching, with a 
considerably longer main shoot, while the branches growing against the 
wmd remain shorter and at times die back. 

Ludwig Klein^ gives very instructive examples in two spruces from 
the pastures above the road Haldenwirthshaus-Wiedenereck. The trees on 
the windy side had lost their branches almost entirely, as if one-half of the 
top had been cut off with scissors (the pruning action of the wind). This 
is ascribed by Klein to the dn,ang action of the wind. To the effect of the 
wind is added an appreciably greater warmth and consequently increased 
transpiration. 

In fruit trees, the flag-like tops often bear fruit only on their outer 
edges, since the interior growth is too dense. When the trunk has been con- 
siderably bent from the perpendicular, a great difference in nutrition shows 
itself between the upper and under side of the branch in the production of 
a more luxuriant foliage on the upper half. The attraction of the luxuriant 
wood shoots for the raw food substances from the soil, brought from the 
roots, increases in proportion to their development. The more they utilize 
this solution, the more is lost for the horizontal part of the tree top, and 
consequently some branches are pressed downward and begin to die, while 
the new leaf axes shoot upward in the perpendicular and form water sprouts. 
Thus is caused a sterility of many years duration. In various forest planta- 
tions near the coast, this one-sided development of the crown is also notice- 
able. The drying of the branches at any rate may be traced partially to the 
constant rubbing due to the wind. The difficulty of reforestration of coast 
stretches should not be explained by the salt content of the sea winds, as is 
often done-, but simply by their mechanical action. 

The stunted forms of trees on coasts and upper limits of the tree line 
is, in most cases, due to the wind. The tips are partly dried and broken off 
by the wind. The weight of snow on the branches may have the same 
result. In the next period of growth the tree attempts to develop a new top 
shoot from one of its lateral eyes, which succeeds in conifers only when 
there is local protection, and only rarely in stormy regions. As a result of 
the broken top, the lateral branches grow with increased rapidity and often, 



1 Klein, L.., Die botanischen Naturdenkmaler des Grossherzogtums Baden usw. 
Karlsruhe 1904, Fig. 26. 

2 Anderlind, Leo, Bericht iiber die Wirkung des Salzgehaltes der Luft auf die 
Seestrandskiefer (Pinus Pinaster). Forstl.-naturwiss.. Zeitsch. 1897, Part 6. 



475 

well covered with needles, lie on the ground. Preda^ describes a good 
example from the Livornian coasts. Besides the slanting trunks, varieties 
of pine and holly Juniperus phoenicea and Tamarix gallica are found bent 
like snakes and the interwoven branches of Phillyrea and other bushes 
creep over the ground. Hansen- gives a very similar description from the 
Island of St. Honorat near Cannes. 

Bernhardt" characterizes certain regions in Germany as centres espe- 
cially frequently visited by storms. As examples should be named Schwedt 
a. O., the Silesian mountains, the Bavarian and upper Palatinate forests, the 
forests of Franconia and, in a limited way, also the North German coast 
(Mechlenburg, Holstein). In these coast lands, northeast storms in general 
prevail as frequently as west and northwest storms, while in Southern Ger- 
many, west and southwest winds have a decided preponderance ; in North- 
ern Germany, as a whole, west and northwest winds. 

It is certain that the distribution of plants will adjust itself to the wind 
conditions, since the varieties which withstand wind better have survived. 
Schrdter and Kirchner* quote, for example, Miiller's explanation of the dis- 
tribution of the tree-like mountain pine {Piniis montana) in the Alps. For- 
merly this was found over a larger area, but because of its slow growth, 
need of light and lesser demand had become hmited to places where a diU'er- 
ent forest vegetation cannot develop, viz., to wind-swept places with scanty 
atmospheric humidity above the forest line. This wind resistance capacity 
of the pine is probably connected with the anatomical structure of the 
needles. Zang and Scheit consider the so-called transfusion tissue of the 
vascular bundles a precautionary structure which, because of its constant 
water content, makes possible the life of the needles in continuous dry air-\ 
Nevertheless, naturally, a definite limit may not be exceeded and Zang^ cites 
as an injury due to wind, the yellowing and drying of the tips of the needles. 

Certainly in conifer needles, the heavy waxy coating of the epidermis 
and the schlerenchymatic sub-epidermal cell row, just as in the cacti, succu- 
lent Euphorbiacae and Crassulaceae, increase the resistance to wind. 
Gerhard^ emphasizes, for the Cape flora, as a further protective arrange- 
ment, the reduction of the intercellular spaces and the depression of the 
stomata. He emphasizes the development of sclerotic hypoderm fibres and 
the strengthening of the edges of the leaf by collenchyma or bast bundles as 
a mechanical effect due to the wind, which manifests itself in spite of the 
moisture of the soil. 



1 Preda, L., EfCeti del libeccio, etc. Bollet. Soc. Bot. ital. 1901; cit. Zeitschr. 
f. Pflanzenkrankh. 1902, p. 160. 

2 Hansen, A. Flora oder Allgem. Bot. Zeitung- 1904, Vol. 93, Part I, p. 44. 

3 Die Waldbeschadigungen durch Sturm und Schneebruch usw.; cit. Forsch. 
auf dem Geb. d. Agrikulturphysik 1880, p. 527. 

4 Kirschner, Loew und Schroeter, Lebensgeschichte der Bliitenpflanzen Mittel- 
europas. Vol.1, Part III, p. 207. 

5 See Scheit Die Tracheidensaume im Blattbiindel der Conifren. Jenaische 
Zeitschr. f. Naturwiss. XVI. 1883. 

ij Zang-, W., Die Anatomic der Kiefernadel usw. Dissertation. Giessen 1904. 
' Gebhard, G., Beitrage zur Blattanatomie usw. Dissertation, Basel; cit. Bot. 
Jahresber. 1902, II, p. 293. 



476 

The very interesting results of experiments made by G. Kraus^ to 
explain sabre growths and other tree forms, induced by the wind, are of 
great importance. If a fresh growing shoot of an herbaceous or woody 
plant be bent so that its tip overhangs, the concentration of the cell sap on 
the convex side has become more concentrated. The increased sap concen- 
tration of the convex side is due to an essentially higher sugar content. 
This sugar is newly formed when the shock takes place. This noteworthy 
peculiarity is exhibited not only by the trunk and branches, but also by the 
half grown and fully grown petioles. The sugar formation, however, is 
not connected with the deformation but depends on the motion as such, and 
frequently when the sugar is formed, the free acid disappears. Ferruza- 
observed in palms and succulents that such interference increased the trans- 
piration ; after Wiesner-' and Eberdt"* had shown that the wind hastened the 
transpiration. It was found by Kohl"^ and Baranetzky*' that even very 
slight interference would increase the amount of evaporation. Reference 
should be made to Burgerstein in regard to further literature'. 

The local distribution of the sugar warrants the conclusion that it is a 
preliminary step, if not a direct one, in the formation of cellulose in the 
plant's metabolism, and it should be stated that, with the increased sugar 
formation in the parts of the plant moved by the wind, the formation of 
cellulose and the development of the cell wall will be hastened. It is a 
comparatively rare occurrence that plant tissues remain in the stage of their 
development in which sugar is formed. More frequent is the process, 
especially in growing shoots, that the sugar disappears to the same extent 
as the cells become thicker walled. We will, therefore, scarcely go astray 
in stating that deformations, resulting from the action of the wind, are more 
stable, since the convex side of the bend forms sugar and cellulose more 
easily; hence its growth is completed sooner. If we consider that the place 
bent is more favorable for the action of light and warmth, then the early 
termination of the period of cell elongation is really a matter of course. 
The branch hardens sooner and does not grow so long; hence, therefore, 
the compact structure of the windward side and the slender, almost whip- 
like branch formation on the side protected from the wind. 

No more thorough discussion is necessary to understand the fact that 
seed beds and young plantations in hght soils may at times be blown to 
pieces, that surface soil may often be blown away and become sterile because 
of the sudden imprudent removal of protective strips of forest and that 

1 Kraus, G., tJber die Wasserverteilung in der Pflanze, II. Der Zellsaft und 
seine Inhalte. Sep.-Abdr. aus d. Abhandl. d. Naturf.-Ges. zu Halle, Vol. XV; cit. 
Bot. Zeit. 1881, p. 389. 

2 Ferruzza, G., Sulla traspirazione di alcune palmi, etc.; cit. Bot. Jaliresber. 
1899, II, p. 124. 

3 Wiesner, Jul., Grundversuche iiber den Einfluss der Luftbewegungen auf 
die Transpiration der Pflanzen. K. K. Akad. d. "Wissensch., Wien, 1887, Vol. 96. 

4 Eberdt, O., Transpiration der Pflanzen und ihre Abhangigkeit von ausseren 
Bedingungen. Marburg 1889, p. 82. 

5 Kohl, F. G., Die Transpiration der Pflanzen. Braunschweig 1886. 

6 Baranetzky, tJber den Einfluss einiger Bedingungen auf die Transpiration der 
Pflanzen. Bot. Zeit. 1872. 

7 Burgerstein, Transpiration der I'flanzen. 1904. 



477 

precaution can be best taken against the various injuries due to wind by 
means of a protective plantation, suited to the conditions. 

We now come to wind-caused injuries to the leaf. The fact that leaves 
become slit or remain hanging, dried and sear, on the branches in. places 
where wind frequently increases to a storm, is so frequent an observation, 
especially in coast regions, that it need not be taken up thoroughly here. 
Just as little need the injuries be touched upon here which are produced in 
unfolding leaves, by the rubbing of the leaf edges'^. Places thus rubbed 
through are found with great frequency in horse-chestnut and beech leaves, 
which, still folded, break from the bud. Young branches are also injured 
by rubbing, as may be observed in the young shoots of pears and weeping 
willows (Sali.v babylonica) after stormy days in summer. Here belongs, 
further, the whipping of hop vines, whereby the catkins at times become 
prematurely ripe and red-. The dried edges of the leaf are more important, 
and as yet but little observed. Since many causes may lead to blighted 
edges, one must distinguish whether the dried and discolored edge forms a 
connected outline or one interrupted in places, or whether dry, discolored 
places push further into the leaf surface from the dead part of the edge 
(frequently wedge-shaped between the main ribs). 

Only the dn', browning or blackening outline may be considered as a 
simple wind injury, as Hansen determined experimentally'. This investi- 
gator constructed* an original apparatus for producing wind in order to 
eliminate secondaiy factors (light, excessive heat, drought) which co-operate 
in the injuries due to wind, occurring out of doors. 

From these experiments, he found, first of all, that passing currents in 
the air dry the tissues most. A simple striking of the wind against a plant 
growing against a firm wall is frequently less injurious and, under certain 
circumstances, actually without elTect because the wall throws back the 
wind current. 

In the experiments carried out with this apparatus, a wind continuing 
day and night, lying between i and 2 of the Beaufort scale, was used. All 
the individual leaves of tobacco plants, standing in pots, after 24 hours had 
slight brownings of the edges, while the remaining part of the leaf blade was 
perfectly healthy and showed no trace of wilting. On an average, the 
mature leaves suffered sooner than the immature ones. The drying of the 
tissue always began near the thinnest peripheral veins. The mesophyll col- 
lapsed, did not contain air but rather appeared translucent, "as if injected." 
The cell content was deformed, the chlorophyll grains could not be clearly 
recognized. In many cells, the protoplasm contained slightly brownish 
granules; the vascular bundles had turned brown; the boundary between 



1 Caspary, Bot. Zeit. 1869, Sp. 201. — Magnus, Verb. d. Bot. Ver. f. d. Prov. 
Brandenburg. XVIII, p. 9. 

2 Beobacbtungen iiber die Kultur des Hopfens. 1880. Herausgeg. v. Deutscb. 
Hopfenbauverein. 

3 Hansen, A., Experimentelle Untersuchungen iiber die Beschadigung der 
Blatter durch Wind. Flora oder Allgem. Bot. Zeit. 1904, Vol. 93, Part I. 

4 Ber. d. Deutsch. Bot. Ges. 1904, Vol. XXII, Part VII, p. 371. 



478 



dry and healthy tissue was sharp and, in the latter, the vascular bundles not 
discolored. Hansen's explanation is that "the current of air fast robs the 
vascular bundles of their water, and so changes them that they can no longer 
act as conductors. Thus the mesophyll dries at this place." This might 
also be the secondary process and the drying of the conducting cords the 
primai-y one, while as yet the drying of the parenchyma of the edge is 
usually looked upon as the direct effect. In opposition to this, Hansen 
says : "If one wishes to assume that the wind directly attacks the mesophyll, 
then it would not be possible to understand why the process of drying should 
not begin also in the middle of the lamina." 

Bruck^ takes up the matter in the same way. He observed that in gen- 
eral only those leaves with the secondary veins extending to the edge, suf- 
fered peripheral injury, the so-called caspedodromous or cheilodromous 
(extending to the edges) venation. (Fig. 96.) Tree leaves from the same 
region, which did not exhibit the injury, had "more or less camptodromous, 

or rather brochidodromous, vena- 
tion ; their course is curved or looped 
without ending at the edge of the 
leaf." In the latter form of vena- 
tion, Bruck perceived a decided pro- 
tection of the leaves against drying 
from wind. Browning of the vascu- 
lar bundles is very similar to that 
produced by frost. 

According to my studies on the 
production of dry edges of leaves as 
the result of the action of gases, the 
process of dying was different here. 
In the action of the gases in smoke, 
the tissue did not become translucent previously and the walls of the bast 
elements color yellow to brown ; the cell content dried together as a whole to 
an approximately uniform substance. The vascular bundles of the peri- 
pheral zone also were altered, but I explained the earlier death of the 
peripheral leaf mesophyll by the fact that even if the fine ends of the vascu- 
lar bundles still supplied water normally, this was not sufficient to cover the 
increased loss due to the action of the acid. It might be just the same in 
the dried edges due to the wind. The evaporation in the mesophyll, increased 
by the wind, may very well be the primary process. The loss of water in 
the leaf is relatively greater at the edge, since the upper surface is too large 
in proportion to the tissue mass and the water conducting system consists of 
too few elements, i. e., is insufficient. At the places where the leaf is thicker 
and the venation more developed, the tissues receive more water and retain 
more, since here the same evaporating surface, as at the leaf edge, has a 





Fig-. 96. 
Craspedodromous Camptodromous 
venation. venation. 

(After Bruck.) 



1 Bruck, W. F., Zur Frage der Windtaeschadigungen an Blattern. Beihett z, 
Bot. Centralbl. Vol. XX, Section 2, Sep. 



479 

much more juicy parenchyma back of it. On this account, close to the 
larger veins, we find strips of tissue which discolor and dry last. 

In this section many striking diseases, held to be due to wind, have not 
as yet been sufficiently studied. An example may be found in the so-called 
Mombacher diseases of apricots, which Liistner^ considers is due to wind. 
In Mombach, near Mainz, apricot leaves dry back from the tip and edge, and 
fall. Sometimes only the dried edge falls, while the rest of the leaf is left 
on the tree. Liistner considers this a wind disease, wdiile Bruck's opinion - 
is that it is a result of sunburn. 

It is more necessary to protect garden plants against the raw spring 
winds than against frost. For example, it was observed in April, 1905, that 
young rhubarb leaves, which withstand frost if they thaw slowly and without 
being touched, were much injured when the frozen leaves had been struck 
by the wind. In the same way young rose shoots were injured only where 
blown by the wind. A\''hile in protected places, young vegetable and flower- 
ing plants stood in perfect condition ; they were destroyed where the wind 
had free access''. Besides the increase in the amount of evaporation, the 
mechanical rubbing of the still tender organ is very destructive. 

In blowing the snow away, the wind does great harm. The seeds of 
various species live in furrows on the side away from the wind even with a 
minimal snow covering, while they die on the windy side. 

Only a properly constructed protective plantation can decrease the 
injuries due to wind. By proper construction we mean, in the first place, 
the imitation of the system which nature adopts in coast regions, and, in the 
second place, the proper choice of trees. 

The natural system consists in the planting of the lowest growing bushes 
on the windy side ; they are stunted or branches die back where beaten by 
the wind, but these dried branches break the force of the wind, letting the 
opposite side develop. If higher bushes are planted behind, they remain 
protected as far up as the height of the first plantation. If they exceed this 
their growth becomes stunted and one-sided, yet, nevertheless, they grow 
somewhat higher and in turn give protection to a tree planted behind them, 
until finally all the trees can grow well. 

Where there is chance that shifting sand may cause trouble, H. Neuer* 
recommends especially Populus alba and varieties of Salix. As intermediate 
plants Ailanthus glandulosa and Rhus Cotinus thrive well. Among bushes, 
Liqustrum vulgarc, Cotoneaster huxifolia, Spiraea opulifolia, Tamarix and 
Ribea sanguineum are especially valuable. Of decorative plants, Pelargon- 
iums, Chrysanthemums and stocks should be used first of all. 



1 Liastner, Beobachtungen iiber die sogen. Mombacher Aprikosenkrankheit. 
Ber. d. Kgl. Lehranstalt zu Geisenheim am Rhein. Berlin 1904, p. 222. Paul Parey. 

2 Bruck, loc. cit., p. 74. 

3 Bottner, Job., Rauhe Winde. Prakt. Ratgeber im Ob.st- und Gartenbau 1905, 
No. 8. 

* Neuer, H., Neue Erfabrungen iiber Anlagen und Pflanzungen an der Nordsee- 
kiiste. Die Gartenwelt 1904, No. 49. 



CHAPTER X. 



ELECTRICAL DISCHARGES. 



Flashes of Lightning. 

In spite of numerous descriptions of destruction in the plant world, due 
to lightning, we have not yet acquired an exact knowledge as to the way the 
lightning acts. Just as in frost injuries, often similar to those produced by 
lightning, we must distinguish mechanical and chemical action; in lightning 
the mechanical action may be the more important one. Cohn^ compiled 41 
cases where lightning had struck and an abundant bibliography. He states 
that when lightning strikes, the main current of the electricity, after breaking 
through the bark, passes down the tree through the cambial layer, which is 
a good conductor. "The heat developed by the action at once vaporizes the 
liquid contents in the cambial cells entirely or in part. The vapor, under 
pressure, either bursts the bark, with the bast clinging to it in strips or 
larger pieces. These broken pieces are frequently thrown off to great dis- 
tances. Besides this main current, a secondary current in the poorly con- 
ducting wood will cause it to split where it is least firm, as a result of the 
sudden drying due to the evaporation of the sap. Therefore, according to 
Cohn's theory, neither the split wood nor the torn off strips of bark should 
be considered as signs of the course of the lightning but only as indicating 
the region of the least resistance. With Caspary, I would rather think that 
the torn strips are the actual traces of the lightning. 

Cohn based his assumption that a sudden vigorous formation of vapor 
due to evaporation in the tissue, struck by lightning, caused the explosive 
scattering of the bark and wood splinters upon the following evidence. 
First of all, dried splinters were actually found. It is possible, however, to 
observe this only rarely since, as a rule, the storm is accompanied by a 
downpour of rain which immediately wets the dried chips. The fact that 
trees may be set on fire by lightning, also favors the drying action. It should 
be stated here, however, that as yet it has not been proved absolutely that 



1 Cohn. Bin interessanter Blitzschlag:. Verh. d. Kais. Leop. Carol. Akad. d. 
Naturf. Vol. XXVI, P. I. — ijber die Einwirkung des Blitzes auf Baume. Denk- 
schrift d. Schles. Ges. f. vat. Kultur 1853, p. 267. 



48 1 

perfectly healthy trees have been set on fire^ ; rather most investigations show 
that only trunks rotten at the core were set on fire. 

The individual condition of trees, as well as the intensity of the light- 
ning, governs the extent of the injur}-. It is found that different varieties 
of trees frequently show similar injuries and that certain kinds are especially 
apt to be struck by lightning, while others rarely. 

It should be stated, first of all, in regard to the nature of the injuries 
that in most cases the torn bark exposes the wood, but that with varieties 
which are good conductors, and in young trees, lightning may strike, leaving 
no visible injury. As a rule, lightning does not strike the tip of the pyra- 
midal poplar, but further down on the trunk, so that most of the top remains 
uninjured ; the lightning then passes down the trunk in a sphntered line 
which is straight or only ver}' slightly spiral. Wood and bark splinters are 
thrown ofT ; on the edges of this strip the bark is raised from the wood, the 
edges themselves are not discolored. In the oak, however, the tip is often 
struck and frequently large branches at the top are killed and broken ofif. 
The splintered strip usually exhibits a strong spiral twisting- on the trunk, 
its wood a more channel-like, hollowed lightning path, while, in the poplar, 
sharply angled splinters indicate the course of the flash. Especially in oaks, 
besides radial splits, the lightning also produces many tangential ones in the 
direction of the annual ring. At any rate, the direction and form of the line 
of splitting depend on the structure of the wood. The lightning follows the 
path of best conduction; hence the more the wood fibres are twisted, the 
more the splinters are twisted. In Fig. 97 F. Buchenau and Nobbe^ repro- 
duced their observations on oak and show the spiral course of the line of 
splitting especially well. Caspary's experiments on the efifect of the sparks 
from the discharge of a Leyden jar. loaded with 50 volts, confirmed the fact 
discovered by Villari that the electrical spark can travel a much longer 
distance longitudinally in the wood than transversely. Besides this, wood 
ofifers a greater resistance to the spark in a tangential direction than in a 
radial one. The relations of the extent and the place struck in longitudinal, 
radial and tangential directions are, according to Caspary, In fresh linden 
wood as 19: 2: I, in dry spruce wood, as 7: 2: i. The tissue was always 
torn in the course of the spark and an extensive destruction of the cell 
contents was perceived as a result of the heat. 

This result from the lightning could be demonstrated everywhere and 
in the cases where no injury is outwardly recognizable, a narrowly limited, 
easily overlooked point of entrance may never be lacking. Colladon* also 
observed, for example, in a poplar and a spruce, especially characteristic 



1 Caspary, Mitteilun^en iiber vom Blitz g-etroffene Baume und Telegraphen- 
stang-en. Schrlften d. phys. okonom. Ges. zu Konigsberg- 1871; cit. Bot. Z. 1873, 
p. 410. Beyer, Blitzschlag. Verb. d. bot. V. d. Prov. Brandenb., 28 .Tan., 1876. 

2 Bucbenau, Abhandl. d. naturwiss. Ver. zu Bremen, Vol. VI. — Schriften d. 
Leopold. Akad. d. Naturf., Vol. XXXIII, 1867. 

3 Dobner-Nobbe, Botanik f. Forstmanner. 4. ed. Berlin, P. Parey, 1882, p. 34. 

4 Colladon, Die Wirkung des Blitzes auf Baume; cit. Biedermanns Centbl. 
1873, p. 153. Bot. Z. 1873, p. 686. 



482 

circular places on the surface from which the bark had been removed. 
These places seem to be produced as a result of the very great local drying 
of young wood and were colored by concentric, dark yellow and brown 




Fig-. 97. An oak 23 m., high, which has been struck by lig-htning. (After Nobbe.) 

'i J?''^'^"; y^^^""^^*^^ split-off branch had joined the trunk, b. c. d branches injured at their base which have 
urieci later, r branch remannng: nnmjured. // and /// hanging pieces of wood, .r and .v small branches 

injured in the sapwood. 

rings. A number of other causes have also become known, in which small. 
circular spots indicate the entrance or exit of the flash of lightning. 

R. Hartig, in his text book^ gives especially clear illustrations of the 

different k inds of injury due to lightning. He traces the difference in the 

1 Hartigr, R., Lehrbuch d. Pflanzenkrankheiten. 3d Edition, 1900. Berlin, J. Springer. 



4^3 

lightning paths to the unequal conductivity of the tissues and to the degree 
of moisture present in them. If rain has fallen, weak flashes of lightning 
cannot penetrate into the interior of the trees, but only tear off pieces of 
bark, lichens and dry branches. Trees which have a very delicate cork 
layer, as, for example, the pitch pine, display sometimes very noteworthy 
traces of lightning only in the outer bark tissue. Often only small, round, 
isolated places in the bark or others connected by zigzag lines are killed, 
which later loosen from the living bark of the tree, often after a preceding 
formation of cork. In trees with a heavy periderm, the lightning must first 
strike through this poor conductor in order to reach the inner bark, which 
is a good conductor Hartig considers the outer layers of the inner bark 
"which are poor in fat" as especially good conductors, while the tissue rich 
in protoplasm and, as a rule, containing much fat in the newest layers of the 
inner bark, is a very poor conductor on account of its fatty contents and 
often entirely escapes the lightning. The best conductive tissue is the young 
wood, having only scanty cytoplasmic wall coatings. This is also found to 
be very susceptible to frost injuries. If (in powerful discharges) the 
cambial layer is also injured, there results an "internal healing." 

The theory of the influence of the fatty contents on the conductivity of 
the tissue is based on the works of Jonescu^. He found that the electric 
spark struck through fresh wood the more poorly, the richer this was in 
fatty oil. In the same plantation the beech is rarely struck by lightning, 
while the oak is most frequently injured. A microscopic investigation 
showed the reason : the wood cells of the beech contained oil ; those of the 
oak were almost free from it. Other "fatty trees" (in which in winter and 
spring all the starch is turned to oil), as for example, Juglans regina, Tilia 
parvifolia, Betula, Pinus, were also found to be bad conductors when com- 
pared with starchy trees (Acer, Corylus, Fraxinus, Ulmus, Crataegus, etc.). 
If the oil was removed from the fatty trees by ether, sparks penetrated the 
fresh pieces of wood just as easily as that of typical starchy trees. It should 
not be forgotten, however, in judging from these conditions, that the oil 
content in the dififerent tree varieties changes in different seasons of the year; 
from this it is evident that their electrical conductivity varies. Jonescu found 
with equally large pieces from the trunk of Tilia parvifolia that in February, 
when wood and bark are rich in oil. a much higher electrical tension was 
necessary than at the end of March, when the young wood was filled with 
starch and glucose. The converse is true in the beech, which from January 
to April, is rich in starch, but in May is rich in oil, as also the pine, spruce, 
hornbean and common oak. The pine is pretty often struck during our 
summer storms. At this time it contains glucose in its wood, bark and pith 
and starch in its medullary rays. But in winter, the tree contains very finely 
distributed oil and it is seen that in countries with winter storms (Ireland, 



1 Jonescu, Dimitrie, Uber die Ursachen der Blitzeschlage in Baumen. Jahresb. 
d. Ver. f. vaterl. Naturkunde in Wiirtemberg-. 1892. Schweizerbartsche Verl. — 
Weitere Untersuchung-en iiber die Blitzschlage in' Baumen. Ber. d. Deutsches Bot. 
G. 1894, p. 129. 



484 , 

Norwa)') lightning almost never strikes pine trees. These differences in 
the composition of the cell contents, however, become of less importance if 
the place of growth causes a high electrical tension, as, for example, if the 
tree stands on impervious layers of soil where water has collected, or on the 
banks of rivers, ponds, etc. 



Fig. 98. Cross-section through a spruce with numerous overgTOwn wounds due to 

lightning-. (After Hartig.) 

The water content of the wood plays a very small part in this question 
of the attraction of lightning by trees. 

The electrical spark under high tension seeks the shortest path and then 
strikes through even poorer conductors. 

Often in the course of years a tree will be repeatedly struck by light- 
ning and cases will thus occur when a trunk shows small roundish or longish 
traces of lightning on its whole outer surface which might lead to the sus- 
picion of hail injuries. Hartig (loc. cit., p. 241) thinks, however, that the 



485 

characteristic form of the hghtning tissue in young wood would remove all 
doubts. Such a picture of repeated and healed injuries, due to lightning, is 
shown in Fig. 98. A similar constitution of the trunk could also indicate 
frost wounds, only here the protruding frost cracks are lacking. Otherwise, 
however, the anatomical changes in the tissue w'hich set in in the sap wood 
during the healing of the wounds due to lightning also exhibit a very great 
similarity to that formation of parenchyma wood which usually follows 
a frost injury. Since we will later consider the latter more closely, we will 
give here, only for the sake of later comparison, R. Hartig's picture which 
v. Tubeuf has recently reproduced^ We see in the lowest, thick-walled 




Fig. 99. - Cross-section through an annual ring of a spruce in the year it was struck 
by lightning. The crumbled cell layer shows the effect of the lightning. 

(After V. Tubeuf.) 

tracheid layer (Fig. 99) the end of the previous annual ring. The new 
annual ring has begun with the formation of thin-walled elements and was 
struck by lightning when the loth to 12th summer tracheids had been 
formed. The action of the lightning consists in the fact that the latest w^ood 
elements have been displaced, slantingly pressed together, as if by a tan- 
gential pulling, and in part killed, while the cell layers, remaining capable of 
life, have developed into parenchyma wood and then gradually passed over 
again into small celled normal wood. 

Healed wounds due to frost exhibit the same processes ; only, as a rule, 
the ahnormal layer of parenchyma ivood is found nearer the old annual ring. 



1 V. Tubeuf, fiber sogenannte Blitzlocher im Walde. 
u. Fortswirtsch. 1906, p. 349. 



Naturw. Zeitschr. f. Land- 



486 

This difference may be due to the fact that the disturbance from late frosts 
occurs usually when the trees have formed but little new wood, while the 
injuries due to lightning are produced by summer storms later in the season. 

R. Hartig did not consider that the production of the collapsed strip of 
tissue was the direct result of the action of lightning, for he says^, "if the 
lightning takes its course, entirely or in part, in the young wood, it is seen 
in this, that the cells remain unlignified and are pressed together by the 
tissue structures produced later." He then gives statements, as does also 
Beling-, on the death of whole groups of trees in which he found'^ that the 
bast was apparently killed in the pines struck by lightning and in numerous 
adjacent trunks. The same observer also mentions a case in a mixed spruce 
and oak forest, in which the spruces predominated, wherein only the repressed 
(12) oaks showed traces of lightning, while the spruces were entirely unin- 
jured. The fact that, in mixed tracts, the oaks suffer with especial fre- 
quency from lightning has often been mentioned; just as also that other 
trees, not distinguished possibly by their height and structure, in certain 
localities fall victims especially to the lightning flashes*. 

In connection with the death of trees in whole groves, R. Hartig lays 
emphasis on his observations that this advances radially in tracts of pine 
trees, v. Tubeuf^ has recently studied this condition. He describes a case 
in which only one larch apparently had been struck by lightning and yet a 
considerable number of the surrounding pines and spruces began to die. 
The larch showed an interrupted line of splitting extending down the trunk, 
the top remaining green. The trees surrounding it showed no local injuries, 
but died in a semi-circle of 25 m. Such cases have often been found. In 
an earlier publication v. Tubeuf states the hypothesis that such dying 
back of large groups of trees is caused by "lightning spray," i. e., by the 
scattering of the lightning into a number of rays pencils ; while Ebermayer' 
traces the phenomenon to an internal lightning stroke, due to the sudden 
union of electricities which had been separated. Through the influence of 
the thunder cloud the opposed electricities divide in the tree; the unlike, 
negative, draws up to the upper part, while the other, positive, presses down 
into the lower part. "Now as soon as the lightning strikes, the cause of the 
separation of the two electricities inside a nearby body is removed and these 
suddenly reunite in the same moment." v. Tubeuf cannot adopt this point 
of view on the ground of the results of his artificial lightning experiments. 
In the investigation of trees taken from lightning depressions, he found, 
"coarse injuries due to lightning" in one or another trunk, and since other 



1 Hartig-, R., Lehrbuch der Pflanzenkrankheiten. 3d ed. 1900, p. 242. 

2 Zeitschr, f. Forst- u. Jagdwesen, Nov. 1873. 

3 Bot. Jahresbericht v. Just, 1875, p. 956. — Lehrbuch d. Baumkrankh. 1882, 
p. 191. 

1 Landwirt 1875, p. 400 u. 513. — Gard. Chronicle 1878, II, p. 667. 

•'■' V. Tubeuf, iiher sogenannte Blitzlocher im W^alde. Naturwiss. Z. f. Land- 
u. Forstwirtsch. ' 1905, p. 493. (Bibliography here.) 

6 Absterben ganzer Baumgruppen durch den Blitz. Naturwiss. Z. f. Land- 
u. Fortswirtsch. 1905, p. 493. Bibliography here. 

T Ebermayer, Wald und Blitzgefahr. Naturwiss. Rundschau. 1899. 



4B7 



causes of death (animal and fungi enemies) were proved to have been 
excluded, he came to hold the opinion that spray lightning must exist. A 
division of lightning into two branches was observed by the head forester, 
Petzold, in the forestry district of Sachsenreid\ 

Blight of Conifer Tops. 

In 1903 V. Tubeuf-, using numerous illustrations, described a case of 
very extensive blighting of conifer tops in upper Bavaria. These observa- 
tions led to the conclusion that only one cause, acting once,. in the winter of 
1901-1902, could have existed and that it must be sought for in an equalizing 
of the electrical potential in zvinter storms. The characteristic symptom is 
the manner of dying. In the up- 
per part of the tip of the tree, the 
bark, bast and cambium are dead, 
further down only parts of the 
bark outside the cambium, so that 
the last can form bast and young 
wood during summer. "The 
white, tender bast then can be 
easily loosened from the sappy 
wood as in healthy trees. The 
dead bark zone joined the newly 
formed bast and, outside this, the 
green bark was still living. Many 
strips of dead tissue, enclosed by 
cork, extended through this green 
bark. .Still further down, the dead 
bast and bark parts were no 
longer bands, surrounding the 
trunk, but were divided into 
strips ; fjnally only dead spots are 
found and some meters below the 

tip of the tree, every sign of disease disappeared. The trunk and the roots 
were perfectly healthy." (Fig. 100.) In the adjoining illustrated cross- 
section from a spruce, bUghted at the tip, the bark is finally killed only on a 
few places in connected strips extending from the outside inward. Other- 
wise, in the bark layer, only scattered smaller centres of browned tissue may 
be found. Since these lie within the living bark,, they are enclosed by a 
layer of white cork. The bast ring seems browned, but broken in different 
places by healthy tissue. 

The correspondence of these charactristics with the changes, described 
by R. Hartig as "lightning traces," led v. Tubeuf to the opinion that this 







;^ 




> 

/ 








1 
1 






i 
J 



Fig-. 100. Cross-section through a blighted 

spruce tip; from the Foi-estry Division of 

Starnberg. (After v. Tubeuf.) 



1 Beobachtungen iiber elektrische Erscheinungen im "Walde. Naturwiss. Z. 
f. Land- u. Forstwirtsch. 1905, p. 308. 

2 V. Tubeuf, Die Gipfeldiirre der Fichten. Naturwiss. Z. f. Land- u. Forst- 
wirtschaft. 1903, No. 1. Continuation ibid. No. 7, 8. 



widely distributed tip blight, appearing suddenly in many individuals, must 
be the result of electricity. The most important point to which the author 
himself calls attention is that lightning usually strikes below the top, injuring 
the trunk, but leaving the crown uninjured; in other observed cases whole 
trees have died, but never the crown alone. In discussing the objections of 
other pathologists who consider that this blight is due to beetles or leaf 
rolling caterpillars (Grapholitha pactolana)^, v. Tubeuf emphasizes the fact 
that the the trees show the characteristic symptoms of disease when the 
bark beetles are absent, and that these, attracted by the smell of turpentine, 
appear only secondarily. Some pines and larches behaved like the spruces. 
In spruces injured by lightning, the dead wood is found in the form of brown 
strips of bark, surrounded by cork, lying within the otherwise green and 
fresh bark, and below the dead tops. v. Tubeuf could not find this either 
in trees which had been broken off, bent or eaten off, nor in others which 
had been frozen or killed by insects. 

Further investigations- proved that the anatomical characteristics of top 
blighted spruces, are identical with those found in trees where lightning had 
produced extensive injuries. The main support of the theory, however, lies 
in the fact that v. Tubeuf and Zehnler^ by means of experimentally pro- 
duced sparks, were in a position to produce, on the living trunk, external 
appearances of top-blight as well as all the similar anatomical pathological 
phenomena, viz., the dead "bark-eyes" which are surrounded by a layer of 
white cork. So long, therefore, as it cannot be proved that other causes 
produce the same symptoms, we must hold to the fact that the kind of top 
blight described is a result of electrical discharges. These, in themselves, 
may be weak, but v. Tubeuf states that in his experiments with deciduous 
trees, and in his observations in the field, electrical injuries do not radiate 
far into the healthy tissue. In artificial electrical injury, the leaves died 
only to a certain point. 

In order to faciUtate the conception of electrical discharge, v. Tubeuf 
calls attention to the St. Elmo's fire* and has produced this experimentally. 
He refers in this to earlier experiments by Molisch^ Inspired by the ob- 
servations which Linnaeus' daughter and son had made on the effect of 
lightning on flowers, he produced a light cluster, i. e., a shiny but quiet 
electrical equalization. 

In V. Tubeuf's experiments, potted plants were insulated by being 
placed on a ball of wax. The soil was connected by a copper wire with one 
conductor of an induction machine and a wire was likewise fastened to the 
ball of the other conductor. As soon as the machine was set in motion the 



1 See Moller in Zeitschr. f. Forst- u. Jagdwesen. 1904, Part S. 

2 V. Tubeuf, tJber den anatomisch-pathologischen Refund bei gipfeldiirren 
NadelhtJlzern. Naturwiss. Z. f. Land- u. Forstwirtsch. 1903, No. 9, 10, 11. 

3 V. Tubeuf u. Zehnder, tJber die pathologische Wirkung kunstlich erzeugter 
elektriseher Funkenstrome auf Leben u. Gesundheit der Nadelholzer. Sonder- 

4 V. Tubeuf, Elmsfeuer-Versuche. Naturwiss. Z. f. Land- u. Forstwirtsch. 
1905, Part 5. 

5 Molisch, Leuchtende Pflanzen. Jena 1904, G. Fischer. 



489 

flower pot, together with the plant, was charged. "If the other wire is 
brought near the plant, a current of the positive and negative electricity is 
seen which had been separated in the two conductors and then in the two 
wires. The positive electricity flows out in the form of a light cluster, the 
negative appears like little beads of light on the tips." Experiments with 
spruces and pines proved that a considerable number of needle tips on a 
plant, negatively charged, gave out the electricity in the form of beads of 
light when approached by the positively charged wire. If, however, the 
plant is charged positively, the electricity flows from the tips of the needles 
without lighf^. 

It was observed in, tender plants that if the positively charged wire is 
held so high above the plant that there were no beads of light to be seen on 
the edge of the blossoms and that no sparks jumped over, no injurieg fol- 
lowed. If this precaution was not observed, after a few minutes the petioles 
and parts of the sprouts below them began to wilt. These appeared darkly 
glassy as after frost or injury. It should be deduced from these experi- 
ments, that quiet electrical discharges can not call forth a direct injury, but 
that such an injury is felt at once if a spark discharge takes place. 

Differences Between Lightning and Frost Wounds in Conifers. 

As yet, in v. Tubeuf's pubhshed results of his experiments, there is 
still lacking an illustration of the anatomic condition of the lightning 
traces which manifest themselves as eye-like spots in the bark. (See Fig. 
TOO.) Although in the works of CoUadon and R. Hartig, mentioned at the 
beginning of this section, we also find statements as to isolated, ring-hke 
traces of lightning, it still seems to me that further experiments must be 
made to demonstrate whether such injuries could not be produced by frost. 
My question has received added force since in deciduous trees I have ob- 
served similar phenomena round about bast groups which, lying near the 
eyes, had been injured by frost. 

In order to get reliable comparative material, I begged from v. Tubeuf 
specimens of his spruce, artificially struck by lightning, and produced frost 
wounds by exposing a healthy five year old pine (v. Tubeuf had also found 
characteristic lightning wounds in pines and larches) in May for a night to 
a temperature of y°C. below zero in a freezing cylinder. The tree, appar- 
ently uninjured when taken from the freezing apparatus, was observed at 
the end of the year. This delay was necessary in order to give it time to 
heal over possible inner injuries as must also have taken place with the 
lightning wounds. 

The pine showed inner injuries only in the bark on one side of the base 
of the trunk ; indeed, partly in the form of isolated dead cells with brown 
swollen contents in the middle of healthy parenchyma; partly in the form 



1 tJber die Unterschiede in der Wirkung der positiven und negativen Elelv- 
trizitat. Compare Plowman, Electrotropism of roots. Americ. Journ. Sc. 1904. cit. 
Bot. Centralbl. 1905, No. 40, p. 342. 



490 



of larger dead cell groups which were enclosed by a living parenchyma wall, 
circular in form ; thereby they formed a figure resembling an eye (Fig. loi). 
In the centre of this eye-like figure frequently a depression was formed (h), 
which was lined by slightly l)rowned, at times almost colorless, cells (u). 
In comparing the pictures, which vary in each section, one became convinced 
that these cells, enclosing the cavity, corresponded to a resin canal lining 
and at times had been pushed out like vesicles into this cavity. This was 
bounded on the outside by a dead bark parenchyma (/>), with only rarely 
collapsed cells and usually of natural size, of which the contents and walls 

77? 



^.... 




.----~p 



Fig. 101. Pine, artificially frosted. (.Orig-.) 

- Isolated dead bark cells with brown homogeneous contents, h cavity in the dead heart of the tissue, 
u slightlv colored or almost colorless lining of the central cavity which, in structure and composition, 
exhibits clearlv the structure of the lining of a resin canal, /> brown bark parenchyma cells from the 
region of the resin canal, completely impregnated with resin, xe parenchyma elongated like plates and 
containing starch. ;/> normal bark parenchyma. 

were impregnated with resin. By clearing the sections, different groups 
of oxalates could be recognized in the dead parenchyma as well as cells with 
grains, which should be considered as starch impregnated with resin. This 
dead tissue was bounded on the outside by the above mentioned circular zone 
of plate-like cells, which in their arrangement resembled a cork overgrowth 
when treated with chloriodid of zinc, but gave a cellulose reaction in their 
walls and were often filled abundantly with starch and small drops of resin 
(r). This overgrowth of the dead tissue centre, which gave the eye-like 
appearance to the frost wound, often passed over into the normal bark par- 
enchyma (r/') which here and there left recognizable traces of starch. 



491 

Fig. I02 shows a cross-section through the bark of a small spruce trunk 
injured by artificial lightning. The trace of lightning (b) shows, first of all, 
a central brown strip-like kernel of swollen parenchyma. This kernel is 
surrounded by a broad, clear zone (k) which consists of radially arranged 
rows of ver}^ thin-walled, nearly empty cells, often containing air. 

Toward the outside, this zone adjoins a tissue ring (kk) of plate-like 
cells, rich in cyptoplasm, the walls of which give a cellulose reaction. These 
cells gradually pass over into the normal bark parenchyma (rp) with its 
large lumina. The resin ducts (g) lying outside the trace of lightning but 
pretty near to it, are, as a rule, uninjured ; the living cells at times projecting 
into the resin ducts are light-walled. This vesicular outpushing of the lin- 
ing cells is a normal phenomenon ; for in branches of healthy spruce in 
winter, resin canals are often found completely filled by tylose-like enlarge- 
ments of the lining cells. Resin ducts also occur isolated in the immediate 
proximity of a trace of lightning in wdiich the cells filling them are changed 
to brown, swollen, resinous masses. 

The dead tissue kernel in the centre of the lightning trace consists fre- 
quently only of dead bark parenchyma. Often, however, it can be noticed 
that some bast groups (h') have participated in this. The fact should be 
emphasized, that the dead parenchyma cells are often entirely collapsed and 
dried. In my opinion, the production of the light colored circular zones, 
composed of thin-walled cells with broad lumina which are found to be actual 
cork cells and constitute the difference from the frost wound, is due to the 
drying up of the cells. 

I conceive of the production of this difiference in the two forms of 
wounds as follows : The electric spark causes a rapid drying out of the 
dead tissue. Since this, like frost, does not cause any slowly spreading, 
subsequent death of the adjoining tissue, vigorous cells, capable of reacting, 
directly bound the dead tissue centres. A reaction to the wound stimulus 
sets in at once if the vegetative activity makes itself felt in the bark. The 
parenchyma around the dead tissue responds to the wound stimulus by cell 
elongation and increase. The cell groups dried by lightning, allow the sur- 
rounding cells to elongate greatly. The more rapidly the process takes place, 
the more material is used up. If this is not present in sufficient amounts 
only a formation of cork will take place and thus the fact is explained that 
after the electrical discharge the bark parenchyma surrounding the dried 
tissue must elongate and divide to fill out the large spaces ; then there is a 
formation of cork. 

When frost kills an area of tissue, lying in the bark parenchyma, at first 
no drying of the tissue takes place. The dead, swollen cells retain their 
size, and are still turgid. Also the pressure of the dying frost-injured tissue 
on the healthy surrounding tissue is not essentially increased. The sur- 
rounding cells have no incentive wdiatever to the great elongation and 
division which were necessary in the drying out of the lightning traces. 
Therefore, there will appear around the dead centre of the frost wound the 




-ir 



Fig". 102. Spruce, showing traces of artificial lightning-. (Orig.) 
b central portion of the trace of lightning in tlie bark parencliynia. // group of normal hard bast. A' group 
of bast enclosed by the lightening tiace, /• cork ring, kk the cell layer resemljling the cork cambium, jr 
resin canal in the healthy bark, from the normal lining of which some cells have curved outward like 
vesicles, gg resin canal, filled with resin, o oxalate crystals, st bark cells filled with starch, ip healthy bark 
parenchyma. <■ swollen tissue grovips in this bark parenchyma, sell bark scales. 



493 

new structure, produced as a result of the wound stimulus and in the form 
of a circular zone of scantier and smaller cells. The plastic food material, 
flowing toward these spots, cannot be longer used for cell increase, since the 
need has been met. It will therefore be laid down in the form of reserve 
substances. Hence the noticeable accumulation of starch directly about 
the frost wound. 

As a positive result of the investigation, it should be cited that in coni- 
fers a definite difference exists between artifically produced, eye-like wounds 
due to lightning and to frost. In wounds due to lightning the dead bark 
tissue dries rapidly and is then surrounded by a porous layer of cork which 
forms a light colored outer ring. In frost wounds, the dead cells in the 
interior of the bark parenchyma at first retain their former size. They are 
enclosed by a circular zone of newly formed cells; these do not develop a 
porous layer of cork, but rather form a slender parenchyma zone, with nar- 
row lumina, which usually is richer in reserve substances than the normal 
bark parenchyma. This zone, in a wound due to lightning, is formed next 
to the cork zone. 

These statements are corroborated by von Tubeuf's observation on the 
differences between wounds due to lightning and to frost. In injuries 
caused by lightning the ring of dead bark radiates into the healthy tissue in 
constantly widening bands, while similar phenomena in the injuries due to 
frost have not been observed in conifers up to the present. 

In regard to the theor}'^ of the action of lightning, the present observa- 
tions on the structure determine that the electric spark primarily produces 
a drying of the tissue. 

Injuries to Trees in Citie.s and Towns. 
With the increased use of electricity in cities, there is a serious menace 
which must be mentioned. Stone's investigations^ show that the alter- 
nating and the direct currents cause injuries by local burning. In dry 
weather, this is less to be feared, but becomes essentially greater when the 
bark is damp. The direct currents used by street car lines come under 
especial consideration here. Besides killing this tissue, the weaker currents 
also stimulate action. Both conditions should be closely examined. Dis- 
charges into the earth during thunder storms are more frequent, according 
to Stone's obsers'ations, than is usually supposed and they explain many 
injuries in the trees, which often are also mistreated by the inconsiderate 
cutting out of the branches in order to isolate the wires. 

Effect of Spray Lightning on Grapevines. 
Among Calladon's- numerous observations on the action of lightning, 
the statement is found that in a vineyard, the upper surface of the soil which 
had been struck by lightning presented a regular, sharply defined circle, the 

1 Stone, G. E., Injuries to Shade Trees from Electricity. Hatch E'xper. Stat. 
Massachusetts Agric. Coll. Bull. 91. Amherst, 1903. , 

- Colladon, Daniel, Effects de la fouclre sur les arbres et les plantes ligneuses. 
Mem. de la soc. de phys. et d'histoire nat., de Geneve 1872, p. 548-53. 



494 

centre showing the strongest action. The vine leaves showed a number of 
spots, which at first appeared dark green and after several days turned 
brick red. In the younger sappy stems, especially the cambium had turned 
brown, while the wood was uninjured. In the injured tissues, the cell walls 
remain unchanged, but the protoplasm was contracted and killed. Rathay^ 
has described the same observation of the distribution of the effect of light- 
ning on numerous individuals and, after mentioning earlier cases, also refers 
to the fact that the same phenomenon of the spreading out of the lightning 
is observed in sheep herds, where likewise several individuals were always 
hit. 

Like Colladon, Rathay also observed that the leaves became red in 
varieties which showed a red autumnal coloring. All the ends of the 
branches died back. The process of the red coloration in leaves has already 
been determined by Wiesner and by me as a result of ringing and bending 
experiments. Rathay supplemented this by observing that the reddened 
leaves transpired much less than normally green ones. Leaves reddened 
after having been struck by the lightning, resembled, in all particulars as yet 
tested, those which turned red from ringing the branches and actually the 
injury from lightning resembled in many points mechanical girdling, since 
here the bark lying outside the cambium was killed. "The cambium of the 
parts struck by lightning remains alive and develops inside the dead tissue, 
toward the outside, a callus surrounded by wound cork and, toward the 
inside, a w'oodring which is separated from the older wood by a thin brown 
layer." The grapes on the vine struck by lightning dried up absolutely. 

We find in a work by Ravaz and Bonnet- different points of importance, 
showing parallelism between the effect of lightning on grapevines and on 
conifers. After calling attention to the fact that a place struck by lightning 
which was planted with 50 to 100 vines, showed that the strongest plants 
were much injured, it should be emphasized that, after being struck by 
lightning on the 20th of May, the tips of the shoots turned down toward the 
ground and dried up. The nodes remained green for some time, while the 
internodes looked almost scalded. The phenomenon of disease gradually 
decreased toward the bottom. Below the dried tips, the pith was torn in 
the injured young shoots and pressed against the woodring. The roots 
remained uninjured. Some weeks after having been struck, the injured 
internodes appeared a reddish brown, shrivelled and cracked longitudinally. 
The tears showed a scar tissue. The intermediary nodes were strikingly 
swollen. Where the tips had not been struck, the branches grew further, 
but had very short internodes. The young wood tissue appeared brown 
and its cells empty and with unthickened walls. The injured parts of the 
bark were enclosed by cork so as to form island-like structures (compare 



1 Rathay, Emerich. fiber eine merkwurdig-e durch den Blitz an Vitis vinifera 
hervorgerufene Erscheinung. Denkschr. d. math.-naturwiss. Klasse d. kais. Akad. 
d. Wissensch. Wien 1891. Extensive bibliography here. 

2 Ravaz, L. et Bonnet, Effects de la foudre sur la vigne. Extr. des annales de 
I'ecole nationale d'ag-ricult. de Montpellier; cit. Bot. Jahresb. 1900, II, p. 417. 



495 

Fig. 102). The cambium formed first an irregular tissue, whicli gradually 
passed o^•er into normal wood (compare Fig. 99). 

From these statements we arrive at the conclusion that lightning (like 
frost) also causes considerable injury by mechanical action and, in fact, as 
a result of sudden excessive differences in tension. The trunk reacts in a 
dift'erent degree according to its age when injured by lightning. Where the 
bark is not injured to its whole extent, the dead places are surrounded by a 
cork layer. If the young wood is not entirely killed but only compressed 
or torn, a parenchyma wood develops later, which slowly passes over into 
normal wood, so that false annual rings can be produced. All phenomena 
spread out gradually from the base of the trunk; that is, they finally 
disappear. 

It is a matter of course that micro-orga,nisms infest all wounds due to 
lightning and it is easily comprehensible that these cases have been described 
as parasitic diseases. An example is offered by "Gelivure" of the grape 
which has been described as bacteriosis, but, according to Ravaz and Bonnet, 
is nothing less than a wound caused by lightning and infested by bacteria'. 

Spray Lightning on Fields and Meadows. 

Steglich- observed one July a potato field which had been struck by 
lightning. The lightning hit in two places and the plants became yellow 
and died ; the stems seemed cracked open and perforated so that the walls 
of the wound appeared torn. 

V. Seelhorst" describes injuries to beets from lightning. In one case 
the place struck formed a circle about 15 m. in diameter. In the middle of 
the circle the beets were all killed. The leaves on the plants near the peri- 
phery were wilted and discolored. Often individual specimens slightly in- 
jured, stood between plants greatly injured. At times small cavities were 
noticeable in the beet, especialty in the head. In other cases, practical 
workers speak of discoloration and weakening of the heads of the beets and 
similar phenoniena ; nevertheless, secondary parasitic influence may have 
made itself felt here. Colladon'* also makes a report of a beet field struck 
by lightning. The leaves of injured plants were colored red, shrivelled or 
torn in places and the edges partially dried. In one potato field the ma- 
jority of the plants in the upthrown soil were found to be healthy; only in 
one place did the base of the potato stem seem torn and burned. In the 
place struck by lightning on a meadow, with a diameter of 6 m., the highest 
thistle tips were killed, while the lower parts and the grass remained healthy, 
although here and there the earth was found to have been torn up. 

To explain the circumstance that the condition of individuals hit on 
similarly planted bits of land always varies, Rathay cites photographs of 



1 Ravaz, L. et' Bonnet, A., Les effets de la foudre et la g-elivure. Compt. rend. 
1901, I, p. 805. 

^ Jahrb. d. D. Landw.-Ges. 1892. 

3 V. Seelhorst, Rubenbeschadigung- durch Blitz. D. Landw. Presse 1904, p. 515. 

* Loc. cit., p. 555. 



49^ 

lightning showing that it usually is not a simple discharge between tw^o 
points, but is scattered and ends in many points. In addition to this, it 
should be emphasized that when grapevines are trained on wires, these 
spread the injurious effect over a greater area. 

V. Bezold's^ statements that, according to the statistics of the Fire In- 
surance Company in Bavaria, the danger from lightning had increased three- 
fold between 1833 and 1882, are especially significant. The extensive 
removal of forests and marsh drainage and the rapid increase of rails and 
electric wire conductors are supposed to play a part in this. 

Disadvantages in Electro-Culture. 

The attempts to use electricity directly in plant cultivation have fol- 
lowed three lines. In the first place, it was desired to increase the assimi- 
latory activity by illuminating with electric light ; in the second place it has 
been attempted to let an electric current pass through the earth by sinking 
two metal discs in the soil connected with some source of current ; in the 
third place, an attempt was made to cause the current to pass directly 
through the plant (or tree). 

As yet the results have been very contradictory, so that no decision 
has been reached. Great hope is set often on the influence of a silent elec- 
tric discharge. This takes place when, for example, a net of wires is laid 
over a field without touching the soil and one pole of an electrifying machine 
is connected with the wire and the other w'ith the soil. In such cases the 
plants act as conductors and through them, by means of the silent electric 
discharge, the electricity will stream out from the tip of the cultivated 
plants. Such a current must actually take place constantly in nature, since 
the soil exhibits an electric charge dift'ering from that in the layers of air 
lying above it. The best known experiments are those of Lemstrom" and 
Pringsheim^. Older works on experiments, in which the electrical current 
is conducted through the soil, had been collected and enlarged by Wollny*. 

The results of Pringsheim's experiments, in which the electricity was 
produced by a static electric machine, sound extremely favorable, since in 
potatoes, sugar beets, beans and straw-berries a quantitatively and quali- 
tatively better yield is obtained. Since, however, many unfavorable experi- 
ences exist, this field, for the present, should not be considered any further, 
as it is not sufficiently cleared up. However, Lowenherz'' work must be 
mentioned because it has been carried through with scientific exactness and 
opens up new points of view. . 



1 V. Bezold. W.. ttber ziindende Blitze im Konigreich Bayern wahrend des 
Zeitraums 1833 bis 1882. Abh. d. Kgl. Bayer. Akad. d. Wiss. II. CI., Vol. XV. 

2 L.emstrom, Elektrokultur. Translated by O. Pringsheim. Berlin 1902. W. 
Junk. 

3 Pringsheim, Otto, Neue Elektrokulturversuche. Osterr. landw. Wochenbl 

1904, No. 24; cit. Centralbl. f. Agrikulturch. 1905, Part 6. 

4 Forschungen auf dem Gebiete der Agrikulturphysik. Vol. II, 1888, p. 88. 

5 Liowenherz, Richard, Versuche iiber Elektrokultur. Z. f. Pflanzenkrankh. 

1905, p. 137. 



497 

The experiments were made with ChevaHcr barley ; a direct current of 
electricity was used which was conducted through the soil. The grains 
were ver}' carefully sown, so that in half the experimental pots the seeds lay 
with their long axes parallel to the direction of the current, thus being 
traversed longitudinally by the current, while in the other pots, the grains 
were laid at right angles to the direction of the current. It was thus found 
that the different position of the grain in relation to the direction of the 
current resulted in a ver}^ unexpectedly great dift'erence in the effect of the 
electricity. 

With the strength of current used (0.015 to 0.030 amperes) an injury 
in the process of germination was universally noticeable, but it could always 
be recognized that the grains, which were traversed longitudinally, germin- 
ated less well than those through which the stream passed crosswise ; yet in 
the first named series, a difference was perceptible in the grains lying 
parallel with the direction of the current, inasmuch as those developed the 
most poorly in which the positive stream entered at the tip of the grain and 
left at the end where the embryo lies. If the direction of the current was 
reversed two or three times within the 24 hours, no difference in the results 
could be produced, but, if the current was changed two times per minute, 
such a difference became clearly evident. The grains laid perpendicular to 
the direction of the current sprouted just as well as seed not electrically 
treated. In those traversed longitudinally by electricity, the disadvantage 
manifested itself noticeably only in the fact that the grains germinated 
12 to 24 hours later. This experiment, which deserves consideration, shows 
clearly that varied conditions must be taken into consideration in cultivation 
with electricity 

Supplementarily, the endeavor to .treat electrically the roots and oldeir 
wood of grapevines by currents of high voltage should be considered here^ 
At the request of the Imperial Agricultural Association at Moscow, experi- 
ments were introduced, incited by reports of combatting Phylloxera by elec- 
tric currents, in which experimental cases, containing roots and cuttings, 
were exposed for 10 minutes to an electrical discharge. Some roots were 
then treated with a spark discharge. It was found that currents of high 
voltage caused an earHer and more favorable development of the vines. 
Roots, however, which had been treated directly by being connected with 
the machine exhibited injuries, for the upper parts did not sprout. Sprouts 
appeared only on the subsoil nodes. 



1 From a review of the "Weinlaube" 1904, No. 34; cit. Ccntralbl, fur Agri- 
kulturchemie 1905, p. 394, 



CHAPTER XL. 



LACK OF HEAT. 



A General Survey. 



Life Phenomena at Low Temperatures. 

The plant is much more dependent on the temperature of the air than 
on the temperature of the soil. Before the soil can follow the fluctuations 
in the warmth of the air, this has already awakened plant life and at times 
brought it to considerable development. The individual parts of the plant 
naturally do not respond to the fluctuations in the temperature equally 
quickly. While the warmth of leaves and thin stems, in the shortest possible 
time, increases or decreases, parallel with the temperature of the air, thick 
trunks will need considerably longer timei, more particularly since all plant 
tissues are poor conductors of heat. From this last circumstance it is 
evident that thick trunks are sometimes warmer than the surrounding air, 
sometimes cooler, and, in fact, are on an average cooler than the air in the 
daytime and warmer at night. But those parts of the plants which extend 
into the air are also cooler in the daytime. The cooling down of the leaves 
comes from their radiation of heat. This will be greater the greater the 
surface of the part in proportion to its bulk. Evaporation should also be 
taken into consideration as a further cause; it proceeds at the expense of 
the warmth of the plant part. These two causes explain the phenomenon 
that, on bright nights, the thermometer shows a temperature several degrees 
lower if it stands directly between densely growing plants with thin leaves, 
such as meadow grass, than is found in the air layer above them. If the 
temperature of the air itself approaches the freezing point of water, the 
parts of the plants may be cooled below zero degrees C. by their heat radi- 
ation and, as a result, die, or. at least, at times some of their functions are 
arrested. According to Sach's^ observations the chloroplasts of the firebean 
(Phaseolus midtiflorus) and maise (Zea Mays) cannot turn green if the 
temperature does not rise to at least 6 degrees C. Rape acts in the same 



1 Lehrbuch III, p. 636. 



499 

way. The stone pine (Pimis Pinea) requires at least 7 degrees C. In 
Potamogeton, the breaking down of carbon dioxid is found first between 
10 to 15 degrees C. ; on the other hand, in Valhsneria even above 6 degrees C, 
and in the leaves of the larch at 0.5 to 2.5 degrees C, and in meadow grass 
at 1.5 to 3.5 degrees C. The movement of the leaves of the sensitive plant 
(Mimosa pudica) first occurs when the temperature of the surrounding air 
exceeds 15 degrees. 

The difference in the amount of heat required by different plants is 
shown best by the obsen^ations made on the germination of seeds in ice. 
Uloth^ found, for example, that seeds of wheat and maple (Acer platanoides) 
germinated in ice and bored their way deep into the ice, which they melted 
by the heat developed during germination. The fine lateral roots of the 
wheat had traversed ice pieces one-eighth of a meter in thickness. Later 
experiments- showed the same observer that several of the Cruci ferae 
(Lapidium rudcrale and L. sativum, Sinapis alba and Brassica Napus), oats, 
barley and r\'e, as well as other grasses, had germinated in large percentages. 
In barley and oats the percentage of germination, however, was noticeably 
less than in wheat and rye. Of the Papilionaceae, 80 per cent, of the peas 
had germinated in the ice-cellar and 12 per cent, of the lentils; 60 per cent, 
of sown parsley seeds showed germination. Incited by these observations, 
Haberlandt^ later undertook further experiments with sowing the common 
agricultural seeds in cases which were kept constantly at a temperature of 
zero degrees to i degree C. by means of ice. After a month and a half, rye, 
hemp (Camelina sativa), red clover, alfalfa, vetches, peas, and bastard 
clover showed the beginnings of germination. After four months, how- 
ever, a further development of the little roots could be proved only for 
mustard, camelina (or gold of pleasure), bastard clover, red clover and 
alfalfa, while wheat, barley, oats, ray grass, buckwheat, beets, rape, poppy, 
white clover, beans, etc., did not reach germination. Of all the plants, 
alfalfa had strikingly proved most favorable. 

These results, in regard to grain varieties, stand in very marked con- 
tradiction to Uloth's conclusions and also to the results of experiments 
which Hellriegel* has published. Of all the plants tested, winter rye was 
proved decidedly to require the least heat. With an almost constant tem- 
perature of o degrees C. (within the six weeks period of the experiments 
the temperature only a few times slightly exceeded this, reaching i degree 
C), this plant developed its leaf and root apparatus perfectly normally. 
Winter wheat was proved to need somewhat more heat because of the small 
size of its germinating plants, and, agreeing with Uloth's results, to a still 
greater degree, barley and oats, which at o degrees C, only slightly devel- 
oped their rootlets, while unable to force the leaf cone out of the grain. At 



1 Fiihlins's Neue landwirtsch. Z. 1871, p. 875. 

2 Flora 1875, p. 266. 

3 Wissenschaftl. praktische Untersuchung-en auf d. Gebiete d. Pflanzenbaues. 
Wien 1875, I, p. 109ff.. 117. 

4 Beitragre zu den naturwissenschaftl. Oryndlagen des Ackerbaues. Braun- 
schweig, Vieweg 1883, p. 284-304. 



500 

2 degrees C, however, the elongation was quite perfect. Maize had not 
changed at 5 degrees C. and even at 8.7 degrees C. germinated very slowly 
and imperfectly. Vetches and rape seed had germinated at o degrees and 
exhibited a development of the seed leaves worth mentioning, while peas in 
greater numbers, and lupins and beans in smaller amounts, had elongated 
the root body, to be sure, but had not developed the aerial axillar}^ part. Of 
seeds which had germinated at 2 degrees C, flax was more sensitive than 
rape seed, which germinated at approximately o degrees, but did not advance 
developmentally or show growth worth mentioning until given a noticeably 
higher temperature (8.7 degrees C). Peas and clover were found to stand 
next to vetches. They put forth a root and leaf at an average temperature 
of 2 degrees C, while beans and lupins needed at least 3 degrees C. for this. 
Asparagus developed slowly at 2 degrees C. For the carrot, approxi- 
mately 3 degrees seemed to be necessary' for germination, and for the beet 
root about 5 degrees C. was needed. 

It is not necessary to state here in detail that naturally the length of 
time of germination increases in proportion to the amount of temperature 
variation from the optimum of germination, but attention might be called 
to the fact that such germination experiments with the lowest possible tem- 
perature could lead to the growing of varieties hardy to frost. In all the 
seeding experiments uneven germination is found. It may be possible that 
those seeds which have first germinated at such low temperatures give plants 
which have a lesser need of heat for all their life processes than do other 
individuals of the same groups. 

Kirchner's experiments^ show that not only the initial stages of ger- 
mination can take place normally at such low temperatures but also that a 
further growth in length is made possible. Kirchner found mustard, rye, 
wheat, peas and hemp growing, as seedlings, for some time at temperatures 
which lay but little above o degrees C. To be sure, plants with a greater 
need of heat still show some growth in length when carried over into a low 
temperature ; but this growth can be explained only as the gradual dying 
out of the oscillations of the energ}^ of growth obtained under earlier, more 
favorable conditions. 

Kerner- has observed with Alpine plants that they can even blossom at 
o degrees. The melting water trickling into the soil from the snow fields 
is able so to stimulate the life activity of such plants that the heat produced 
by their respiration is able to melt the ice crust when it is even 2 to 5 cm. 
thick, so that the green organs reach the open air (Soldanello). 

Autumn Coloration. 

The coloring of the leav^es in the autumn is not always the same for the 
same variety. It seems that the difference is caused by the habitat of the 
individual. In general two types can be distinguished ; either a perfectly 

1 4. Vers, deutscher Naturforscher u. Arzte zu Salzburg, p. 75 d. Berichtes. 

2 Berichte d. naturwissenschaftl.-mediz. Vereins zu Innsbruck, Sitzung vom 
15. Mai 1873, cit. Bot. Z. 1873, p. 438. 



501 

normal process of yellowing is found, beginning at the edge of the leaf, and 
followed by the; drying of the tissue, toward the centre of the leaf, or the 
yellowing and drying do not follow parallel, but rather opposite paths, i. e., 
the process of turning yellow begins at the petioles and the larger veins and 
advances toward the periphery, so that the edge is colored last of all, while, 
nevertheless, the first to dry subsequently. I observed the last course espe- 
cially well in Acer platanoidcs, less constantly in Acer Pseudoplatanus. The 
middle surface showed an uniform brilliant quince yellow, while the peri- 
pheral zone was still green. With advanced lowering of the temperature, 
many leaves showed a turning brow'n and dying of the outermost edge of the 
still green part of the leaf periphery, while the yellow, middle field did not 
yet show any dead places in the tissue. 

This case can also occur with Tilia, and in fact usually on one side, 
.iince only half of the leaf shows the process. Nevertheless in the linden, 
the coloration, advancing, from the edge toward the centre, is more frequent. 
The investigations of numerous cases show that the irregularities of color- 
ation are connected with the irregular dying of the vascular bundles. 

The normal autolysis in the autumn sets in when the whole vascular 
bundle system of the roots has still retained its functioning and the dying 
back only begins at the finest ends of the nerves at the edge of the leaf. 
Then the leaf discolors and dries first along the edge ; the discoloration ad- 
vances gradually in the portions of the leaf between the smaller veins and 
finally also between the larger ones toward the midrib and the petiole. If, 
on the other hand, the functioning of the ducts is prematurely destroyed in 
the branch or in the petioles, which can be perceived from the browning of 
the vascular bundles, then the discoloration begins at the petiole, or the 
larger veins, and extends irregularly toward the periphery. 

The course of the dying back, due to continued summer drought, re- 
sembles the normal autumnal autolysis, inasmuch as the parts of the leaf 
receiving the least amount of water are the first to discolor. Besides the 
drying of the leaf edges, however, that of the middle region of the larger 
intercostal fields becomes more noticeable here, because these lie fartherest 
from the strongly developed conducting strands ; thus especially great de- 
mands are made upon them because of excess of light and heat. 

The autumn coloring begins with a change of the chlorophyll often 
accompanied by the appearance of a red coloring matter. At first a change 
in the position of the chloroplasts is noticed, and a tendency to unite. I 
found in the spruce that the individual chloroplasts form radiating processes 
which unite with those of the adjacent ones. The red coloration is condi- 
tioned by the presence of ferments and related bodies. Many evergreen 
plants turn a dirty brownish green. According to Kraus^ this coloring is 
produced as follows : fine grained protoplasmic masses, colored a bright 
reddish green to copper red, occur in the palisade parenchyma in place of 



1 Kraus, tJber die winterliche Farbung immergriiner Gewachse. Sitzungsber. 
d. phys.-med. Soc. Erlangen; cit. in Oekonomische Forstchritte 1872, Nos. 1 u. 2. 



502 

the disappearing chloroplasts. The further the cells of the leaf flesh are 
separated from the brown upper surface, the more transitions are noticed 
from these reddened cytoplasmic masses to the normal chloroplasts. 

All these changed tissues may, in many cases, be brought back to the 
normal color, if cut branches are brought into a warm place. In this, how- 
ever, the intensity of the light is not increased, and this may explain why 
only a lowering of the temperature should, in general, be considered as the 
cause of the autumn coloring. A further proof lies in the fact that in the 
autumn natural ripening only the ripened places, i. e., the places most cooled 
down by heat radiation, change their color, while the parts inside the top of 
the tree and covered by the outer leaves, show no change. 

In regard to the change in the coloring matter of the chlorophyll, it has 
been proved by Frank^ and Wiesner- that the chlorophyll passes over into a 
substance which Pringsheim called "Hypochlorin"^. This is an oily body, 
usually dark colored, which is produced from chloroplasts by the action of 
anorganic and organic acids and finally crystallizes into needles or whip-like 
brown crystals. Tschirch* has proved that this hypochlorin is identical with 
the "Chlorophyllan" of Hoppe-Seyler and that it should be considered as the 
first product of the oxidation of the chlorophyll (and in fact of only one 
part of the raw chlorophyll, viz., the cyanophyll of G. Kraus). This product 
is formed of itself if a chlorophyll solution is left standing for some time^ 

Tschirch found that the formation of chlorophyllan or hypochlorin, 
increasing according to the amount of acid, could be proved (tytrimetri- 
cally, by means of normal alkali) in the parts of the plants. Besides water 
plants, there may be only a few plants, the cell sap of which does not have 
a marked acid reaction. In genera which contain little acid, the formation 
of the chlorophyllan will be small and the extract made from this will have 
to stand some time, while in strongly acid plants (Aesculus, Rumex) the 
oxidation proceeds so fast of itself that no purely green extract can be made, 
since it at once exhibits the peculiarities of the modified chlorophyll and, 
even when chilled, deposits chlorophyllan. 

It is worth mentioning, for our consideration, that according to Tschirch 
even carbon dioxid is able to change the chlorophyll into chlorophyllan. 
Also the tannic substances with which the red coloring matter is certainly 
related, will have to be reckoned among those bodies with an acid reaction 
which attack the chloroplasts. It is thus a question whence it comes that 
this discoloring influence of the acid cell sap makes itself felt in the chloro- 
plasts only in the autumn. This can be explained either because in the course 
of the summer so little free acid is available in proportion to the rest of the 



1 Sitzungsber. d. Bot. Ver. d. Prov. Brandenburg XXIII, v. 24. Feb. 1882. 

2 Bemerk. iiber d. Natur d. Hypochlorins. Bot. Centralbl. 1882, Vol. X, p. 260. 

3 Untersuchungen iiber Lichtwirkung. Pringsheims Jahrbiicher 1880, Vol. XII. 

4 Sitzungsber. d. Bot. Ver. d. Prov. Brandenburg XXIII, v. 28. April 1882. 

5 Concentrated hydrochloric acid breaks down the chlorophyllan into a body 
dissolving in hydrochloric acid with a blue color, the "Phyllocyanin" of the authors, 
and a brown body insoluble in hydrochloric acid, but soluble in ether, the "Xanthin" 
of C. Kraus. (Tschirch, Untersuchungen iiber das Chlorophyll III. Ber. d. deutschen 
Bot. Ges. Vol. I, Parts 3 and 4; cit. Centralbl. 1883, Vol. XIV, No. 25, p. 356. 



503 

substances in the leaf cell that the chlorophyll used in the formation of the 
chlorophyllan is constantly and quickly replaced by the preponderant process 
of assimilation, in which case usually no yellow coloration of the chlorophyll 
body is noticeable, or the chlorophyll body may be protected by a substance 
which does not let the acid through, gradually losing this protection in the 
autumn. However, both processes might take pace and, according to the 
above experiments, this is most probable, 

Frank and Wiesner refer to the actual presencei of an arrangement in 
the chloroplasts which protects them against the attacks of the acid cell sap. 
They emphasize that the green grains lie imbedded in protoplasm which is 
impervious to acids. Tschirch has also mentioned that each chlorophyll 
grain is surrounded by a colorless cytoplasmic membrane (hyaloplasma- 
layer) which is especially easily proved in water plants, and in this way 
possesses a special protection against the acid cell sap. 

As the leaf cell approaches the end of its life in the autumn the proto- 
plasm is no longer very abundantly present. But even where it is still more 
abundant, it undergoes, in the cold of the autumn, a change (which may be 
overcome by heat), making it permeable to acids. Frank found that the 
yellow coloration, produced by the action of acid on the chloroplasts, had 
already occurred when they, together with the nucleus, lay closely imbedded 
in the cytoplasmic wall layer. Such a change in the diosmotic character- 
istics of the protoplasm of evergreen trees also makes possible the action of 
acids. The organic acids increase, however, in the autumnal leaf in this 
way, making easier leaf coloration. 

In regard to the red coloration, C. Kraus^ has proved that the Brenz- 
catechin (orthodihydroxbenzine) first found by Gorup-Besanez- in wood- 
bine occurs in all leaves which change color in the autumn even (so far as 
the partial investigation extended) in all leaves still growing vigorously. 
This substance turns green with ferric chlorid and a beautiful red with vege- 
table acids. The extracts of the leaves give the reactions of oxyphen acid, 
on which account the conclusion is pertinent that the red coloring matter in 
the young leaves and in those which have changed color in the autumn 
comes from the increased effect of the Brenz catechin, due to the increased 
action of the acid. 

Summarizing all that has been said previously we can consider the 
process of the autumnal change of color as a process of oxidation, increased 
m proportion to the process of assimilation and due to the effect of light. 

This acts very differently on the substances present in the cells of the 
various plants, so that the chlorophyllan is produced from the chlorophyll 
coloring matter and the leaf becomes yellow.^ If the Brenz catechin, 
which may be produced artificially from carbo-hydrates and probably is 



1 tJber die Herbstfarbung der Blatter und die Bildung- der Pflanzensauren. 
Biedermanns Centralbl. 1874, I, p. 126. 

2 Annalen der Chemie und Pharmacie 1872, Vol. CKXI, Parts 2 and 3. 

3 The chlorophyllan extraction of leaves dead in the autumn shows the same 
"bandes accidentelles permanentes" as Chantard emphasized earlier (Centralbl. f. 
Agrikulturchemic 1874, p. 40). 



504 

present in opalescing drops, is changed into a red coloring matter by means 
of an autumnal abundant formation of acid, a reddening and yellowing of 
the leaves follow. The leaf turns brown, however, if on the other hand, 
there predominates the formation of brownish yellow masses observed by G. 
Kraus^ and Haberlandt- with the destruction of the form of chloroplasts, 
which masses C. Kraus considered as the products of oxidation and humi- 
faction of the carbo-hydrates and which, as I believe, can directly arise from 
the decomposition of the chloroplasts. 

The most frequent, but certainly not the only cause of the red color- 
ation, is the lowering of the temperature, whereby the action of the light 
becomes relatively excessive. It is not the absolute values of light and heat 
which are determinative here, but the relative ones, i. e., those coming under 
consideration in relation to one another. A lowering of the temperature 
reduces the process of chlorophyll form^ation, while it sustains in full activ- 
ity that of oxidation, which, forming Brenz catechin, requires more light^, 
and initiates the red coloration. If the activity of the chlorophyll apparatus 
is increased, i. e., more carbo-hydrates are formed, the accessible oxygen is 
no longer sufficient for so high a degree of oxidation and the process of red 
coloration is suppressed. If, however, the work of the chloropyll is arti- 
ficially retarded by a lack of nutriment and moisture, then the oxygen acces- 
sible in the cell can suffice to reoxydize to a high degree the material which 
has become more scanty; in this case the autumn color occurs even in 
summer. 

As has been mentioned already, I observed in August, wdth girdling 
experiments on Crataegus, that the autumn coloring occurred even during 
the intense heat of summer and that at times it was possible with somewhat 
more solid leaves to bring the tip of the leaf which had been left on the; tree 
to a bright red autumn change of color by breaking the midrib while the leaf 
base, lying below the sharp point of breaking, retained its normal deep green 
color. Besides this, in the course of the, summer, we find, in many plants, 
ihat the first formed leaves of the annual growth, which have quickly lived 
out their Hfe, assume their autumnal coloration in the heat of summer 
(Ampelopsis). Places on young red leaves, which have been covered, 
remain greener. We will take up these conditions again under "Defoliation 
due to frost." The winter preparation of evergreen plants will be taken up 
thoroughly in the section on "Theories as to the Nature of Frost Action." 

Frosting and Freezing to Death. 

In the literature on this subject, we find different conceptions of the 
term "freezing to death." Death which gradually sets in in a plant because 
it has not obtained the warmth necessary for carrying through its normal 
functions has been explained in part as freezing. On the other hand, only 

1 Okonom. Fortschritte 1872. Nos. 1 and 2. 
^ Biedermanns Centralbl. 3 876, II, p. 48. 

3 Batalin. tJber die Einwirkung des Lichtes auf die Bildung des roten Plg- 
mentes. Acta Hort. Petrop. VI. 



505 

the death which occurs suddenly as a result of a lowering of temperature 
below the minimum boundary of heat requirement and which is connected, 
as a rule, with the formation of ice, may be considered as "freezing to 
death." 

We can best overcome this difference in the use of the terms if we 
consider the first injury, due to a lack of heat, as a "chronic injury" and 
sudden death as an "acute injury." 

Tender plants from the tropics, which in our greenhouses do not con- 
tinuously find the heat necessary for all their developmental phases, often 
furnish examples of chronic injury. Failures in the culture of Indian 
varieties of Anoectochilus and other tender-leafed orchids. Begonias, Ges- 
neraceae, Marantaceae, etc., are well known. I found their leaves becom- 
ing brow^n-specked, curling and dying if exposed for some time to a tem- 
perature of 3 degrees above zero to 5 degrees below zero\ In wet, cold 
years, open ground culture of melons, cucumbers, tobacco and beans became 
diseased when the lack of heat was prolonged. 

In acute injury, one is inclined involuntarily to ascribe it to the forma- 
tion of ice. That this in itself does not cause death is shown in many cases 
by our hardy plants, which often are frozen stiff and as brittle as glass and 
yet continue their growth after the frost has disappeared. 

Let us picture to ourselves the effect of the formation of ice in the 
tissue. If the temperature of the part of the plant has fallen to the freezing 
point or somewhat below it, small ice crystals are formed on the outside of 
the cell wall. These crystals, produced at first from the absorption water 
and later from the imbil)ition water of the cell wall, become constantly 
larger, since, at their base, more and more water from the mycellar inter- 
stices of the cell wall is changed to ice. Finally, all the fine ice prisms are 
united into an ice crust. The cell w^all has attempted to make up for the 
loss of water which it has undergone by taking up new amounts from the 
cell contents. 

Thus the protoplasmic body of the cell becomes poor in water, and 
material changes begin, which finally reach such an intensity that the 
equilibrium of the different mycellae of the cell wall and of the proto- 
plasm is permanently disturbed. They change in such a way that no more 
life activity is possible. The cell, killed by frost, thus shows that its walls 
offered no resistance to the pressure of the cell sap, gradually letting it flow 
away. In direct contact with the air, this passes over into decomposition 
and the cell itself collapses. The frozen part of the plant appears wilted 
and dried, or rapidly decays. The cell sap, passing out of it, — this initiates 
the decay, — presses through the mycellar interstices and not through any 
breaks in the cell wall which might have been produced by frost. Indeed in 
a frozen part of the plant the tissue can be blasted by the ice in different 



1 Compare also Molisch, Hans, Das Erfi"ieren der Pflanzen bei Temperaturen 
iiber dem Eispunkte. Sep. Sitzungsber. d. K. Akad. d. Wiss. Wien. Mat.-naturw. 
Klasse, Vol. CV, sec. 1; cit. Z. f. Pfianzenkrankh. 1897, p. 23. 



5o6 

groups and, as frequently observed, the cells of the epidermis can be raised 
from the underlying parenchyma, while a rupturing of the individual cells, 
due to the freezing of the water, has as yet been rarely observed. There- 
fore, the theory formerly generally expressed and now frequently held by 
practical growers, that the frost kills the plants by rupturing the cells, has 
been given up as untenable. 

In the same plant the same degree of cold can be uninjurious at one 
time and fatal at another, according to whether thawing takes place gradu- 
ally or suddenly. This latter case may be observed if frozen leaves or 
herbaceous stems of soft-leaved plants are held in the warm hand. The 
places of contact frequently become black after thawing and die. We will 
return to these phenomena in the following. 

Rapid and violent changes in temperature within a scale above zero 
degrees C. also did not remain ineffective. Sachs^ has proved that each 
rapidly appearing rise or fall of temperature is followed by an increase or 
decrease of the rate of growth. While de Vries could observe no disad- 
vantageous results from such fluctuations, I found a dropping of the leaves 
in the most extreme cases, especially if the fluctuations took place in a scale 
which began several degrees under zero and rose considerably above zero. 
The same plants in fact die if a change of temperature is repeated several 
times within a short period, as shown by Goppert's experiments-. Milk- 
weed {Euphorbia Lathyris) was taken from a temperature of 4 degrees C. 
below zero into a room at 18 degrees C. The leaves, bent backward and 
against the stem, because of frost, were raised at once and assumed their 
normal horizontal position. The same process was found in a repetition of 
the experiments, which took place five times within two days. On the third 
day the raising of the leaves began to be less and after eight days the plants 
were dead. Here, therefore, the cause of death was the rejpeated action of 
slighter degrees of frost, while out of doors, and uncovered, they could 
qndure 10 to 12 degrees below zero for some time without bad effects. The 
same experiments gave similar results with many other plants. This ex- 
plains the observation in general practice that slighter degrees of cold in 
many places kill plants which, at the same time, in a place with more con- 
stant temperature, can endure much greater cold. 

Goppert also calls attention to another fact which may serve to explain 
the frequent contradictions in regard to the fatal action of slighter degrees 
of frost in those plants which usually defy greater cold. It depends espe- 
cially upon the conditions under which the plant may find itself at the time, 
as shown by the experiment with the common groundsel (Senecio vulgaris) 
and meadow grass (Poa annua). Pots of these plants, which had already 
withstood a temperature of 9 degrees below zero, were placed for 15 days in 
a greenhouse at 12 to 18 degrees C. above zero. After this time they froze at 
a temperature of 7 degrees below zero, while other examples of the same 



1 Lehrbuch d. Bot., 3d ed., p. 638. 

2 tJber die Warmeentwicklung in den Pflanzen usw. 1830, p. 62. 



507 

varieties, which had remained out of doors during this time, weire found 
absolutely uninjured by rapid thawing. The killed plants had been made 
more tender by the retention in the greenhouse. Kornicke^ also comes to 
the same conclusion in his observations that French varieties of grain, on 
an average, more often fall victim to frost than the varieties which originate 
from the provinces of Prussia and Silesia. The longer cultivation in a 
country with a mild winter has made the varieties less resistant. 

Under otherwise equal conditions, Haberlandt- found that the seed- 
lings of field beans, field vetches, carrots, barley, peas, rape, poppy, red 
clover, alfalfa and flax, grown in a greenhouse at 20 to 24 degrees C, were 
frozen to death even at 6 degrees C. below zero; rye and wheat at 10 to 12 
degrees below zero, while plants of the same variety, grown at the same time 
in a cold frame, died only at 9 to 12 degrees below zero, and rye and wheat 
only at 20 to 24 degrees C. below zero. 

The plants and parts of plants whose growth has entered upon a dor- 
mant period, on an average, suffer less and it is well known that dried seeds 
survive uninjured many degrees below freezing, while they go to pieces in 
a germinating stage with much slighter frost. 

During the vegetative development the susceptibility to frost changes 
with the different phases of the cell life. 

In unfolding apple blossom buds, which had suffered from a spring 
frost, I found the youngest cells, richest in protoplasm, were not injured, 
but those somewhat older, in an energetic stage of elongation, had turned 
brown, while the still older parenchyma cells in turn seemed healthy. 

The cases, cited up to the present, show clearly the difficulty in giving 
definite thermometer degrees as fixed minimum and maximum boundaries 
for the developmental capacity of any species. Each plant is certainly con- 
nected with a definite scale of heat, but the boundary and optimum values 
may change, to a certain extent, according to the combination of the remain- 
ing vegetative factors, momentarily present, which earlier contributed to 
the construction of the individual. 

On the other hand, it must be maintained that in spite of all the vege- 
tative conditions, which increase susceptibility to frost, many plants (espe- 
cially numerous algae, mosses and Alpine plants) never show any damage 
from frost. We will have to explain this phenomenon by the fact that the 
need of heat of such plants is so small that the greatest reduction in tem- 
perature is generally insufficient to produce those molecular changes in 
the tissues which would prevent a reassumption of the normal life functions. 

Theories as to the Nature of Frost Action. 
After discussing the circumstances which modify the freezing of plant 
parts, we will consider the theories which have been formed as to the nature 
of frost action. 



1 Annalen d. Landw.; cit. in Neue landw. Zeitung v. Fiihling 1871, Pai't 8, 
p. 586 ff. 

2 Haberlandt, tJber die Widerstandsfahigkeit verschiedener Saaten. Wissensch. 
praktisch. Untersuchungen, Vol. I. 



5o8 

In this, the phenomena of crippling, due to chronic action of cold, no 
longer come under consideration ; for these phenomena are primarily normal 
functions which are only retarded grJidually by a lack of heat until life 
becomes extinct^ The matter is quite different in the acute cases where 
death follows immediately upon the cold. 

In the acute frost phenomena, the formation of ice becomes a consider- 
able factor. This does not occur, hov/ever, at the point where pure water 
freezes but only below o degrees C, because the cell sap represents a salt 
solution. Besides this, observations, of which those of Miiller-Thurgau" 
especially should be cited, show that ice is produced only after the freezing 
point has been exceeded to a certain degree, either to an excessive chilling or 
supercooling. As an example of how often the supercooling point lies 
considerably below the freezing point, a few statements of the above named 
investigators may serve as examples. 

In grapes, the freezing point (G) was found to be at 3.1 degrees C. 
below zero, the supercooUng point (U) at 6.7 to 7.8 degrees C. below zero; 
in apples and pears, 1.4 to 1.9 degrees C. below zero (G) and 2.1 to 5.1 
degrees C. below zero (U) ; in potatoes i.o to 1.6 degrees C. below zero (G) 
and 2.8 to 5.6 degrees C. below zero (U), etc. 

The formation of ice occurs suddenly ; therefore, in cases where some 
supercooling has taken place, there follows a sudden change in temperature. 
Our hardy plants, which can still grow unimpaired after they have become 
brittle with ice, show that the formation of ice is fatal only for certain 
varieties. In other cases, however, it has been observed that parts of plants, 
under certain conditions, can be cooled down to a still lower temperature 
and remain alive, while, with lesser cold, but different conditions, they are 
frozen as soon as the formation of ice has taken place. 

This formation of ice, the process of which we have already described 
thoroughly, is now ascribed by Miiller-Thurgau^ and Molisch* to such a 
withdrawal of water from the cell, that the cell dies on this account. Ac- 
cording to this, death from frost would be a simple process of drying up. 
The investigators support their theoi-y by the physical process, that, in 
freezing swollen colloidal substances, pure w^ater will be cr>'stallized out, 
and the colloidal substance, thus gradually drying, becomes stiff. 

In contrast to the above theory, is the one we hold, that death from frost 
is no specific process of drying but should be sought in a molecular irre- 
parable destruction of the protoplasmic structure. This destruction is 
expressed mechanically as well as chemically. The destructive tempera- 
ture is specific for each variety, each individual, each part of the plant and 
each method of growth of any plant part, but is not directly connected with 



1 Compare Kunisch, H., tJber die totliche Wirkung niederer Temperaturen auf 
die Pflanzen. Inauguraldissertation. Breslau 1880. — Sachs, Landw. Versuchs- 
stationen 1860, p. 196. 

2 Landwirtscliaftl. Jahrbiicher 1886, p. 490. 

3 Ix)C. cit., . 534. 

4 Molische, tJber das Erfrieren der Pflanzen. Jena 1897. 



509 

the formation of ice, as was evident in the number of plants which, without 
injury, endure the formation of ice in their tissues. These plants are called 
"resistent to ice" and they freeze only if the parts, which have been frozen 
stiff, are cooled down below this specific minimum. 

This specific minimum is not fixed but rises with the amount of cell sap, 
i. e., death from cold occurs at a higher temperature and, conversely, a loss 
of water will cause an increase in resistance to all factors^ and therefore, 
with frost, will cause death only at a lower temperature. 

Mez- adds to these the following observations : Any aqueous solution 
of a substance must be cooled down below the freezing point of water 
before ice can be crystallized out. In dilute solutions, as they exist under 
normal circumstances in cell sap, the lowering of the freezing point is pro- 
portionate to the molecular concentration (Raoult's law^). Dalton's law in 
regard to the solution of osmotic substances which contain several sub- 
stances in solution, holds good here. According to it, the amount that the 
freezing point is lowered ec}uals the sum of those amounts which each sub- 
stance would produce of itself. 

Since now each cell in the same plant may have a content gradually 
diflfering from that of the other cells, the point of minimum cooling of the 
cell sap will be a constantly changing one. Since the composition of the cell 
sap within the latitude of the specific limits of all varieties of plants fluctu- 
ates according to the nutrition, it is easy to understand that the various 
individuals possess a different resistance. This also explains the different 
behavior of dry and juicy parts of plants. The fact that in seeds, which 
may be dried, death can result also from a removal of water is explained by 
Miiller and Molisch by the assumption that it takes place because of the 
sudden formation of ice in the supercooled plant, whereby the water is very 
rapidly removed. Pfefifer* opposes this hypothesis and his book contains 
a thorough treatment of the pertinent literature. Mez's studies, already 
mentioned, support Pfefifer, for his investigations led to the following 
results. The fall in temperature, indicating the end of crystallization, did 
not lie, in any of the objects tested, below 6 degrees C. below zero. (The 
experiments were made with petioles of Helleborus, Saxif raga and Strelitzia, 
with leaves of Sempervivum and sprouts of Opuntia, Asparagus, Begonia, 
Peperomia, etc.). 

"But the cell sap, capable of coagulation and not absorbed, stiffens be- 
tween o and 6 degrees C. below zero. Accordingly, at 30 degrees C. below 
zero, no greater dr)'ing of the protoplasm, resulting from the removal of 
water in the formation of ice, takes place than at 6 degrees C. below zero. 
A plant which always survives the formation of ice in its tissues, does not 



1 Pfeffer, Pflanzenphysiologie, 2d ed., p. 315, note. 

2 Mez, Carl, Neue Untersuchungen iiber das Erfrieren eisbestandiger Pflanzen. 
Sond. Flora Oder Allg-em. Bot. Z. 1905, Vol. 94, Part I. 

3 Raoult's law: cit. Nerst, Theoretische Chemie, 4th ed. 1903, p. 152. 

4 See the chapter on "Die TIrsachen des Erfrierens'' in "Pflanzenphysiologie," 
II. Vol., 1904, p. 314. 



5IO 

die, therefore, as a result of the dying of the protoplasts, but of a coohng 
down below the specific minimum." 

We find in this a confirmation of our earlier standpoint, viz., no simple 
process of crystallizing out the water is caused by the action of the cold but 
a material disassociation. This action of the cold makes the life functions 
impossible. Besides these essentially mechanical processes, however, chem- 
ical decomposition often plays a part. This will be initiated sometimes by 
too great cooling, sometimes without it. Not every plant needs to be first 
cooled down in order to freeze, but it probably freezes more rapidly, i. e., 
is cooled down to a sub-minimum temperature, if the freezing occurs in 
association with supercooling. At least this is shown by Mez's experi- 
ments with pieces from the stem of Impaticns parviflora. We learn from 
these experiments how very much the supercooling depends upon the con- 
stitution of the cell sap. Gases, dissolved air, hinder or decrease super- 
cooling just as do emulsified oil. gum or plant mucilage. It is also found 
that pruned plant parts, cooled down in water, always freeze without any 
further reduction of temperature or, at least, without an essential one. It 
happens that plant stems, standing partially in water, are found to be frozen 
as far back as they extend into the air. Molisch tested the question experi- 
mentally by letting branches of Tradescantia zehrina lie half in water. 
During the night a temperature of 5 degrees C. below zero acted upon them. 
After a slow thawing in a cool room, the half of the sprouts which had been 
left in the air were found to be frozen, while the lower half, sticking in the 
ice, remained uninjured. The upper half, surrounded by air, will have 
been cooled down rapidly by supercooling and is thereby frozen. On the 
other hand, as far as the plants stood in water, the cooling down takes place 
slowly on account of the high specific warmth of the water, and the super- 
cooling will be hindered by the freezing water about the stem as well as by 
the ice in the tissues above the water, which have been frozen. 

An observ-ation made by Miiller-Thurgau, that in a heap of beets, the 
outer frozen roots protect the inner ones from freezing, calls attention to 
the specially favorable influence of the formation of ice. This point is 
emphasized by Mez, since he says in general that the transformation of the 
cell sap into a solid aggregate condition forthwith protects from too rapid 
radiation the energy still retained in the plant. The conducting of heat is 
ver>^ much lower in ice than in water in which the warmth is distributed by 
currents. 

The danger of freezing, i. e., the lowering of the temperature to the 
specific death-deahng minimum, can in part be promoted by secondary cir- 
cumstances and in part hindered by them. The decrease lies in the use of 
the specific heat of water ; this will be mentioned again in methods of pro- 
tection against frost and further in the formation of ice itself, which occurs 
at zero, or a very little below it, while death sets in only at lower tempera- 
tures or finally in a change of the cell sap, since a greater quantity of oil, 
gum and mucilage acts retardingly. 



511 

The increase of the danger of freezing to death exists in all conditions 
which hasten the appearance of a fatal supercooling. 

Thus, for example, the anatomical structure of the individual, depend- 
ing upon the vigor of nutrition, can influence this. In very luxuriant 
growth, the lumina of the cells and ducts are wider and the intercellular 
spaces larger. However, the wider the duct, the more the lowering of the 
freezing point is suppressed by capillarity. We find this fact emphasized 
by Bruijning\ He found that the extract of Taxus leaves, in narrow 
capillary tubes, has a freezing point of 8.8 degrees C. below zero, while the 
same extract in open reagent glasses freezes at 1.3 degrees below zero. 

Besides the greater amount of water in the tissues, the constitution of 
the air (amount of humidity contained) and its movement come under con- 
sideration. In the later connection, attention should be called to the wide- 
spread discovery that, in protected positions (in narrow valleys, fields sur- 
rounded by woods, etc.) plants freeze which would remain uninjured in 
regions accessible to the wind. 

In order to explain this circumstance, we will have to recall the fact 
that air in motion increases evaporation and thus concentrates the cell sap. 
With stronger evaporation the formation of ice will occur more quickly, 
whereby supercooling will be avoided, and, at the same time, protection 
of the remaining heat in the tissue will be brought about. 

In its prevention of supercooling by the superimposed ice, may be 
found the advantage of the "open furrow" for winter grain ; it retains 
snow much longer. 

Fog will also act as a protection. We find a recent example of this in 
the observations made by Thomas", who, in Thuringia, found that the foli- 
age of young beeches, on the heights covered with fogs was uninjured, 
while in the valleys it was brown and wilted as a result of frost. In this 
case, an evident boundary line could be found. In mountain forests, the 
covering of clouds is a protection against frost which one should not 
underestimate. 

We will now turn once again to the fact that in many cases a rapid 
thawing of frozen plant parts can bring about death, while a slow warming 
does not kill. The correctness of this assertion is often contested. If it is 
given as an universal rule, it seems inconclusive; but if it is limited to cer- 
tain cases, it certainly is of value. An older and very instructive example 
is given by Karsten^. A large shipment of tree ferns (Balantium) had to 
withstand 20 degrees below zero enroute. .Some of the plants, when they 
arrived, were put, in a still frozen condition, into a warm place and were 
killed, while almost all of those first thawed in cold water and then taken 



1 Bruljning, F. F., Zur Kenntnis der Ursache des Frostschaden. Sond. 
Wollny's Forschungen auf dem Gebiete d. Agrikulturphys. 1896; cit. Centralbl. f. 
Agrikulturchemie 1898, p. 173. 

2 Thomas, Fr., Scharfe Horizontalgrenze der Frostwirkung an Buchen. Thiir- 
inger Monatsblatter 1904, 12. Jahrg., No. 1. 

3 tjber die Wirkung plotzlicher bedeutender Temperaturanderung usw. Bot. 
Z. 1861, No. 40. 



512 

into a cold place, remained alive. From this, it is evident that the rapid 
thawing and not the frost is the cause of death. 

Miiller-Thurgau has stated of ripe fruit and Molisch of the leaf of 
Agava americana, that these objects can be kept alive after moderate freez- 
ing, if thawed very slowly, but that they die when thawed rapidly. 

I pressed the surfaces of the frozen leaves of herbaceous Cinerarias 
between my finger tips. The plants, left in their places of growth, showed, 
after thawing, that only the places pressed with the fingers were killed. 
According to the discoveries of gardeners, it is only the tender-leaved, juicy 
spring blossoming plants, grown ' in greenhouses (Cinerarias, herbaceous 
Calceolarias, etc.), which, after a night of freezing, can be rescued by the 
longest possible retardation of the thawing. 

In plants perfectly resistant to ice, however, the rate of freezing and 
thawing seems to have but little influence on life. 

In explanation of the matter, two points should be taken into consid- 
eration. First, in rapid thawing, the same processes will be enacted which 
occur, for example, in the evaporation of fluid carbon dioxid whereby the 
formation of solid carbon dioxid takes place, as is well known. In rapid 
thawing, the warmth necessary for melting will be removed, not only from 
the surrounding air, but also from the deeper layers of this part of the plant, 
which are thereby cooled down still more. In such plants in which the 
critical point, i. e., the specific minimum, lies close below the freezing point, 
this removal of heat, increased by rapid thawing, can cause death. 

The second point to- be taken into consideration is that the cell wall, 
from which ice has been crystallized, cannot possibly soak up the great 
amounts of water which are produced suddenly by rapid thawing. The 
water remains in the intercellular spaces and evaporates there while the cell 
of the leaf is not able to regain the necessary turgid condition. From this 
comes the gardening method of protecting from the rising sun all plants 
which have suffered from late frosts. 

Let us consider finally the natural processes of the autumnal changes 
of material from the standpoint of Mez's theory as here discussed. When 
the plants prepare for winter, they collect the greatest possible amounts of 
reserve substances and reach the maximum at different times, according to 
their individuality. In Pimis austriaca, for example, Leclerc du Sablon^ 
found this maximum in May, but in the spindle tree (Evonymous Euro- 
peus), which sends out its shoots earlier, he found it in March; in decidu- 
ous trees the maximum is reached in the fall. In evergreen plants, the 
reserve carbo-hydrates remain abundant in the leaves-. Their activity 
seems reduced to a minimum, since their stomata are closed permanently. 



1 Leclerc du Sablon, tjber die Reservekohlehydrate der Baume mit ausdauern- 
den Blattern. Compt. rend. 1905, p. 1608; cit. Centralbl. f. Agriculturchemie 1906, 
p. 322." — Pabricius, L., Untersuchungen iiber Starke- und Fettgehalt der Fichte 
usw. Naturwiss. Z. f. Land- u. Forstwirtschaft 1905, p. 137. 

2 Simon, Der Bau des Holzkorpers sommer- und wintergriiner Gewachse usw. 
Ber d. D. Bot. Ges. 1902, p. 229. 



PART VII. 



MANUAL 



OF 



Plant Diseases 



BY 



PROF. DR. PAUL SORAUER 



Third Edition— Prof. Dr. Sorauer 

In Collaboration with 

Prof. Dr. G. Lindau ^nd Dr. L. Reh 

Private Decent at the University Assistant in the Museum of Natural History 

of Berlin in Hamburg 



TRANSLATED BY FRANCES DORRANGE 



Volume I 
NON-PARASITIC DISEASES 

BY 

PROF. DR. PAUL SORAUER 

BERLIN 



WITH 208 ILLUSTRATIONS IN THE TEXT 






Copyrighted, 1917 

By 

FRANCES DORRANCE 



6^- 



©C!,A476180 



SEP 20 1917 

THE RECORD PRESS 
Wilkes-Barre, Pa. 



"^v^ \ 



513 

Thes€ reserve substances are protected so far as is possible against frost. 
Part of the starch wanders into the protected central portion of the trunk 
and branches (pith, medullary rays and parenchyma wood), and part is 
transverted into sugar or occurs instead as a fatty oil. In the needles of 
Alpine spruces, the substance of the chloroplasts is found to flow away and 
the cell content in winter forms a homogeneous cytoplasmic mass with 
abundant oil drops. Lidforss^ has proved this transformation for all the 
green cells of evergreen plants ; in the spring the starch is reformed. 

This removal of solid bodies from the cell with the appearance oi 
winter takes place, according to Mez, as an advantageous arrangement in 
|)lants resistant to freezing. He calls the fluid substances "thermally active," 
for, in crystallization, they set free heat. The solid elements, on the other 
hand, follow retardingly the temperature of the fluids ; they are "thermally 
passive" and absorb heat, since, with the formation of ice, the change of 
temperature from the point of supercooling towards zero, they must again 
give up this heat relatively rapidly. This circumstance acts in such a way 
that, with the accumulation of solid bodies in the cell, the melting point 
of the cell sap cannot be reached after supercooling has taken place. A 
great number of thermally passive elements consequently form a menace 
for the plant, while the fluid, thermally active bodies are proved advan- 
tageous as producers of heat. Profiting by the experiments of A. Fischer-, 
we will distinguish between oil trees and starch trees, according to whether 
they change their starch into oil or let it pass into the interior of their trunks 
and branches and convert it into sugar in the bark. The fatty oil of oil 
trees (conifers, birches), which we have learned to recognize from Jonescu 
as a protection against lightning, besides this peculiarity of preventing 
supercooling, like sugar, is thermally active, i. e., stores up heat to be given 
out in crystallization. The trees which transform all their starch into oil, 
conifers, may be fitted to survive a higher degree of cold than those in which 
a part of the starch is left free and becomes sugar only in the bark (the ma- 
jority of deciduous trees). This circumstance surely explains the phe- 
nomenon that conifers and birches extend farther up into cold regions. 

Disturbance due to Chilling. 

Cases occur in potted plants in greenhouses, in which the plants suffer 
when carried from one house to another, in case they are thus exposed to a 
temperature below zero degrees at times for only a few minutes. Practical 
gardeners maintain that the plants have "taken cold." 

Moebius^ has studied this statement very recently, and has been able to 
confirm the above assertion. For example, he took a Begonia metallica 
from a warm house, kept it one or two minutes out of doors in a tempera- 
ture of 5 degrees C. below zero and then put it again in its former place. 

1 Lidforss, Zur Physiologie unci Biologic der wintergrunen Flora. Bot. 
Centralbl. 1896, p. 33. 

-• Jahrb. f. wiss. Bot. 1891, p. 155, cit. by PfefCer loc. cit., p. 137. 

3 Mobius, M., Die Erkaltung der Pflanzen. Ber. d. D. Bot. Ges. 1907, Vol. XXV 
pt. 2, p. 67. 



514 

Even the same day, he noticed newly produced brown spots on some of the 
older leaves. Later these leaves got a "glassy, dark appearance, jiung 
down and dried up." The young leaves did not suffer. The same kind 
of discoloration and wilting phenomena were observed in other similar 
experiments and are in all essentials the characteristics which have been 
given by practical growers as a result of taking cold. Moebius emphasized 
that no formation of ice in the tissues can be concerned here. I can bring 
proof of this in an experiment which I made with Begonia anjyrusti(jma. 
A pot of this plant was taken from a warm house and put out of doors 
after the temperature had risen to 0.5 degrees C. Within a short time, I 
saw glassy spots appear on some leaves. 

According to the experimental results given in different places in the 
present chapter, I perceive in the wilting and glassiness of different leaves, 
with sharp falls in temperature the results of sudden differences in tension 
in the tissue. The contraction of the cells as a result of the excessive cool- 
ing will cause, in places, an outpressing of water into the intercellular spaces. 
Besides this, the difference in the different tissue forms united in the leaf 
organ makes itself felt. We will refer in this connection to the subsequent 
section on frost blisters where various elevations of the epidermis and loos- 
enings of the tissue are described. 

The practical grower at any rate should keep in mind the fact that, in 
transporting plants from warm houses, there is a possibility of taking cold, 
even if plants are exposed only a few minutes to a freezing temperature. 
Since a sharp change of temperature should be avoided, the wrapping of the 
pots with cloth or paper must be recommended for all cases. 

B. SPECIAL INSTANCES OF FROST ACTION. 

Turning Sweet of Potatoes. 

In the well-known phenomenon, that potatoes turn sweet when sub- 
jected to slight degrees of frost, Goppert^ and Einhof- had noticed that in- 
dividual differences make themselves felt. Under the same conditions only 
part of tlie tubers turned sweet and remained soft, while the others became 
hard. If the potatoes were brought quickly into considerable cold (about 
10 degrees) the)^ were frozen, as a whole, without showing any formation of 
sugar. The turning sweet could not be observed except at temperatures 
which lay only a little below the freezing point. Miiller-Thurgau found 
that this change set in only in potatoes which had been taken from the soil 
at least a month earlier. It could not be produced in freshly harvested 
tubers. Probably similar phenomena led Payen^ to the conclusion that even 
before the action of the frost, the tubers, which showed the formation of 
sugar, might have started to grow again. 



1 'Warmeentwicklung-, p. 38. 

- Neues allgem. Journ. f. Chemie. Berlin 1805, p. 473. 

3 Cf. Czapek, Fr., Biochemie Uer Pflanzeen. Fischer, Jena, Part 1, p. 371. Here 
also notes on older literature. 



515 

The fact, established by EinhotT and Goppcrt, that potatoes freeze with 
greater degrees of cold without becoming sweet and that those which have 
become sweet remain soft, is explained simply by Miiller-Thurgau's^ experi- 
ments. He found that the potato tuber freezes only at 3 degrees C. below- 
zero. To be sure, its real freezing point lies possibly about i degree below 
zero, but the cell juices must first be cooled down to 2 to 3 degrees below 
freezing, i. e., be "supercooled," before the first ice crystals can be formed 
between the cells. Naturally, a lowering of the temperature from zero to 2 
degrees below zero retards many life processes. Among these are two which 
come especially under consideration here; viz., the transversion of the starch 
into sugar and the utilization of the sugar. It may be assumed that the 
sugar from the protoplasm of the cell is partly used in respiration, partly 
during the period of growth in the regeneration of the cytoplasm and the 
starch reversion. Miiller-Thurgau- found, in fact, that potatoes which had 
become sweet after having been kept at a temperature of 20 to 30 degree C. 
had increased their starch content at the expense of the sugar. This had 
disappeared ; with a lowering of the temperature to o degrees and 2 degrees 
below zero, the process of respiration (and most probably also that of the 
regeneration of the protoplasm) decreases, while the transversion of the 
starch into sugar does not fall off so quickly. Consequently, the sugar 
accumulates in the tuber and becomes noticeable in the flavor. It amounts 
to about 2.5 per cent, of the fresh substance, yet comparatively wide fluctu- 
ations are found in difi^erent individuals of the same variety. A higher 
w^ater content in the tubers favors the turning sweet. This increase of sugar 
corresponds to the loss of starch yet, according to Czubata's'^ analyses, no 
corresponding proportion can be proved in the two processes. According to 
Czubata, a part of the protein passes over from tlie insoluble into the soluble 
condition during freezing. Muller assumes that the ferment here concerned 
increases with the lower temperature. 

If potatoes which have become sweet are left for some days in a room 
with a temperature of more than 10 degrees, respiration increases and the 
sugar is oxidized, i. e., the potatoes lose their sweetness and in this way 
again become usable for cooking. Other proposed means, as, for example, 
the leaching of the tubers with water, did not lead to any results. Besides 
this, however, it should be emphasized that one need not hesitate to use 
potatoes for seed which have become sweet. Such potatoes freeze only 
with a greater degree of cold than non-sweet tubers'*. 

I should like to add here supplementarily a statement made to me 
verbally that in Reinerz a cellar is said to exist in a cave in which potatoes 
become sweet even without the action of frost. This phenomenon is 



1 Miiller-Thurgau, Ein Beitrag zur Kenntnis des Stoffwechsels in starkehal- 
tigen Pflanzenorganen. Botanisches Centralbl. 1882, No. 6. 

2 Landwirtsch. .Tahrb. 1883, p. 807. 

^ Czubata, Die chemischen Veranderungen der Kartoffee beim Frieren und 
Faulen. O.ster.-Ungar. Brennerei-Zeitung 1879; cit. in Biedermanns Centralbl. 
1880, I, p. 472. 

i Muller-Thurgau, Landwirtsch. Jahrb. 1883, p. 826. 



5i6 

ascribed to a strong exhalation of carbon dioxid. I have not been able to 
prove experimentally an increase of sugar in the tubers, by a two days' 
retention in a carbon dioxid atmosphere. Nevertheless, it might be possible 
that some eifect would be noticeable after a lonja^er time. The statement 
gains probability from a work by Bachet^ and Savelle. according to which, 
by the use of carbon dioxid with a somewhat higher temperature and greater 
pressure, starch flour was rapidly turned into dextrine and grape sugar, espe- 
cially if the process of saccharification was facilitated by the addition of 
gluten. It can be assumed that, because of an abundant supply of carbon 
dioxid in the above mentioned case from Reinerz, natural respiration is 
repressed just as by a lower temperature and the process of sugar formation 
which, according to Miiller, can be proved up to a temperature of lo 
degrees has caused its slow accumulation. The production of saccharose 
during germination after an increase of temperature is proved by Mar- 
cacci's- experiments with slices of potato which had been dried in the sun 
and in an oven. In the sprouting tubers, saccharose is found in the young 
shoots and later in the leaves (probably due to the hydration of starch). 

It is evident from the above that the methods of using these potatoes, 
which in outward appearance are rarely distinguishable from healthy, non- 
sweet tubers, can in no way be applicable for frozen ones, i. e., those turned 
to ice. A tuber which has been frozen hard is dead and, in thawing, at 
once falls victim to a high degree of decomposition. It becomes soft and 
gives off water, while the cut surface turns brown at once, if not immedi- 
ately coated with acid. The skin separates quickly from the flesh, like a 
bladder, with a development of gas. The bark cells beneath the cork layer 
break apart because of the dissolution of the intercellular substance. The 
cytoplasm is brown and granular and drawn back from the cell wall; the 
protein crystalls are dark brown ; the cell sap is strongly acid. 

The Running to Seed of Beets. 

By this name are characterized those specimens of sugar beets and fod- 
der beets which set seed even in the first summer. In some years the phenom- 
enon occurs very frequently and disturbs the harvesting and use of the beet 
since the root is woodier than in the two-year-old beets. Opinions differ 
as to the cause of the phenomenon. They take two different points of view ; 
some make the constitution of the seed responsible for this, others, the 
atmospheric conditions and especially spring frosts. In consideration of 
the fact that actually in years when late frosts have attacked the young beet 
plants, unusually many may be found which have run to seed and, sup- 
ported by Aderhold's experiments with kohlrabi, to be mentioned later, we 
will give here the present cultural retrogression. 

From the abundant literature on sugar beets we will cite only one work, 
since it reports recent scientific in\estigations and makes brief references 

1 After Compt. rend 1878; cit. in Biedermanns Centralbl. 1879, p. 544. 
- Marcacci, A., Sui prodotti della transformazione dell' amido, cit. Bot. Jahresb, 
1891, I, p. 47. 



517 

to the older experiences. Andrlik and Mysik', on the ground of numerous 
analyses, have come to the conclusion that the weight of the seed-bearing 
tuber may sometimes be less than that of the normal tuber, at other times 
greater. The root of the. seed-bearing tuber is poorer in potassium, phos- 
phoric acid and sulfuric acid as well as ammonium nitrate and amido- 
nitrogen. The sap is purer. Of the organic substances formed by the 
seed-bearing beet, the sugar content amounted to only 45 to 50 per cent. ; 
in the normal beet 54 to 69 per cent. "The greater part of the organic sub- 
stance, free from sugar, is in the pith. i. e., in the elements forming the solid 
skeleton of the plant. * * * ." "The pith formation probably takes 
place at the expense of the sugar." 

We perceive that the beet plant has changed its inbred method of 
growth. Instead of storing, in the first year, only reserve substances in 
the root and making use of them in the following year for the formation of 
seed, it at once makes furthci use of the organic substances gained by the 
leaf apparatus. 

This circumstance points to the fact that the normal process in the cul- 
tivated beet, the uninterrupted formation of new leaves, has undergone 
some disturbance. The growth has ceased for some time, rather the beet 
has passed through a dormant period which would correspond to the winter 
rest of a normally ripened tuber. The newly mobilized reserve material 
is used here for the production of the inflorescence, just as in the normal 
case, after the arrestment of growth. It is conceivable that the late frosts 
may call forth such an arrestment. They will incite a greater formation of 
seed stems, the later in the year they occur and the more the subsequent 
weather favors inflorescence formation. If, however, the weather, follow- 
ing the frosty night, is especially favorable for the development of foliage, 
the elongation of the axis, already begun, can stop and the development of 
the root advance. In large sugar beet fields, as a rule, such seed-bearing 
beets and similar transitional forms are found. This inclination to the set- 
ting of seed can certainly be hereditary in the seed, possibly can be prepared 
in the seed of normal beets, if not sufhciently matured, i. e.. for example, if 
harvested before it is ripe, 

Aderhold- has furnished experimental proof of the formation of seed- 
bearing roots in Kohlrabi, as a result of frost action. He brought seedlings 
in pots into a freezing chamber for 8 to 10 hours and then placed them out 
with others which had been exposed to frost. In one experiment; he ob- 
tained, ior example, two seed-bearing roots from 18 untreated plants, while 
from the same number of specimens which, for 10 hours in May, had been 
exposed to a temperature of 2 to 6.5 degrees C. below zero, he had 7 seed- 
bearing plants. In both cases some Kohlrabi plants later overcame the 
impetus of frost action and formed a root body. 



1 Schos.srii)ie unci normale Rtibe. Blatter f. d. Zuckerruben))au 1905, No. 24, 
p. 374. 

2 Aderhold, R. uber da.s Sehie.ssen des Kohlrabis. Mitt. d. K. Biolog. Anst, 190(5, 
No. 2, p. 16. 



5i8 

It is well known that, in some years, such premature development of 
inflorescences occurs often in other plants, which form fleshy, storage 
organs (celery, carrots, radishes). It is very probable that not only frost 
action but also other processes of arrestment are effective here. 

Frosty Taste in Grapes. 

The processes which occur in the turning sweet of potatoes take place 
also in woody plants. In this connection, Pfeffer' mentions Fischer's inves- 
tigations- on the fluctuations between the starch and sugar in the so-called 
starch trees, such as the linden and birclv'. When branches are taken in 
winter from out of doors into a warm room, starch is formed in the bark 
parenchyma, within a few hours, and. in the cold, can again pass over into 
sugar. A similar formation of sugar, connected with the decrease of 
organic acids, is found to occur in grapes after the action of frost. 

Even when the main stem of immature clusters had been attacked by 
frost but was still green and the berries clear, a considerable decrease of acid 
and increase of the sugar content was founds An investigation on Riesling 
grapes of the decrease of acids in a plant which had been exposed from 
October 19 to November 9 to a temperature as low as 5 degrees C. proved 
an acid reduction of 4 per cent. Half ripe clusters, greatly injured by frost 
when cut ofl", showed from October i to 11, an acid loss of 4.5 per cent. 

The frosty taste, however, does not seem to be due alone to the increase 
of sugar and decrease of acid, but material compounds may perhaps diffuse 
from the stems of the grapes which the protoplasm of cells would not have 
let pass through, if there had been no frost action. Through these changes, 
the susceptibility of the grapes to the fungus of white rot may be increased, 
since Viala and Pacottet'' have shown that this fungus is able to infest only 
the berries which have a high sugar and a smaller acid content. The be- 
havior of l)lack rot is exactly the reverse. 

Changes in the Blossom Organs. 

In the action of frost, the permanent processes are sometimes chemical, 
sometimes mechanical. In the former it is difficult to decide in how far they 
are initiated by the freezing, or if they begin only with thawing. Thus for 
example. Gopperf^ has observed in the blossoms of Phajus and Calanthe 
that they turned blue when frozen. This change in color is explained by 
the fact that, through the action of the frost, the indicans, which* is abun- 
dant in the normally colorless cells, especially around the vascular buncjles, 



1 Physiologie, 2d edition, I, p. 514. 

•^ Jahrb. f. d. wiss. Bot. 1891, v. XXII. 

:! tJber die Periodizitat der Stiirkezu- und abnahme in den Baumen. Compare 
Mer, E. in Bot., Jahresb. 1891, I, p. 46. 

■i Biedermanns Centralbl. 1879, I, p. 233. 

•"' Viala, P. et Pacottet, Sur la culture du black-rot . Compt. rend. 1904, 
CXXXVIII.'p. 306. . c. ^, 

'•■ tJber Einwirkung des Frostes auf die Gewiichse., Sitzungsber. d. bchles. 
Ges. t. vaterl. Kultur 1874, cit. Bot. Zeit. 1875, p. 609. 



519 

is oxydized to indigo. Prillieux^ states that this change appears first with 
thawing. Other statements on the beha\ior of the coloring matter in blos- 
soms vary as greatly and it can only be said in general that the red coloring 
matter is one of the most resistant ; in fact, according to Goppert-, who has 
collected many observations on the color phenomena produced by frost, it 
can be increased in the leaves and blossoms with slight frost action. 

Most frequent, and therefore most important, are the disturbances in 
the blossoms of our fruit trees due to frost. For all practical purposes, the 
way the process of discoloration takes its course is immaterial. Scien- 
tifically, however, it may be of interest to become more exactly acquainted 
with the frost action. But since it is impossible to determine in natural 
spring frosts what are the first efiiects and what the subsequent changes, I 
have subjected apple blossoms to artificial frost. 

After a blossoming apple branch had been exposed for 2 hours to a 
temperature of 4 degree C. below zero, the investigation, carried on imme- 
diately after the removal of the freezing cylinder, showed that all the petals, 
and also some places in the leaves, had taken on a glassy consistency. 

Even after a few minutes (the air temperature was 11 degrees C.) 
a flabbiness and a turning brown began in the parts which had become 
glassy. The brown discoloration of the leaves, therefore, is not the direct 
effect of the cold but a phenomenon making itself felt first with thawing. 
The petals, with the natural reddish tinges on the under side, had brown 
veins and were spotted. The edges began at once to collapse and dry up. A 
cross-section showed that the discoloration was due less to the turning brown 
of the cell walls than to that of the cell content, since these excreted reddish 
yellow to brownish yellow solid masses deposited usually in the longitudinal 
axis of the cells and resembling carotin. The different cell layers of the 
petals behaved differently. The excreted yellow masses could be proved to 
be especially abundant beneath the colorless epidermis which had remained 
at its natural height. Besides this, the parenchyma cells which accompany 
the vascular bundles of the fine veins showed these excretions especially 
distinctly. This latter circumstance caused the venation of the fine petals 
to appear strikingly brown to the naked eye. With the rapidly advancing 
process of drying, the cells of the mesophyll collapsed, while the cells of the 
epidermis retained their natural size. 

Fig. 103 shows a part of a petal soon after it had been removed from 
the freezing cylinder. It shows the leaf still in its natural dimensions, with 
the large intercellular spaces (/) between the very thin walled cells of the 
flesh and with the unchanged epidermis (r). The discoloration, due to the 
yellowish brown contracted mass of the cell content {b) , is most intense 
near the vascular bundles (g) and in fact especially so on the under side of 
the leaf. In the vascular bundle the narrow spiral ducts have turned brown. 



1 Bot. Zeit. 1871, No. 24.— Bull, de la Soc. hot de FVance 1872, p. 152. 
-' Kunisch, H. ttber die tr«dllche Wirkung- niederer Temperaturen auf die 
Pflanzen. Inauguialdissertation, p. 29. Breslau 1880. 



520 

The browning process took a diflerent course in the stamens. After 
they had been taken out of the freezing cyhnder they remained apparently 
unchanged, while the petals had already begun to wilt. Only later did the 
stamens become yellowish brown and the anthers a pale yellow. A cross- 
section through the stamens showed that the brown coloration was essen- 
tially conditioned by the epidermis which is rich in contents. To be sure, 
in all the tissues, the cell contents seemed contracted into drops or lumps 
and were brown, but the amount of substances in the inner cells was so 
scanty that the coloring of the whole tissue remained pale. The spiral ducts 
of the stamens, like those in the petals, had light brown walls. In the 
anthers, the discoloration depended likewise on the amount of cell contents. 
These were most abundant in the connective tissue and this consequently 
seemed most deeply brown, while the epidermis in the anthers themselves 
and the underlying fibre cells, arranged like palisades, had only very scanty, 
solid masses of contents and, therefore, seemed almost colorless. The rem- 



Fig. 103. Cross-section of a petal of the apple injured by artificial frost. 

nants of the ground tissue near the connective tissue were somewhat 
darker. 

The pistils showed the greatest injuries. They were a deep brown and 
bent when taken out of the freezing cylinder. At first no collapse of the 
tissue could be seen anywhere. The papillae of the stigma seemed stifl:" and 
filled with Ijrown cytoplasmic contents. As in a fresh condition, they still 
held fast the somewhat swollen and, therefore, differently formed pollen 
grains, filled with cloudy, uniform contents. In the pistil, as in the stamens, 
the peripheral layers were richest in content and, therefore, their contents 
and walls most deeply colored brown. 

Among the mechanical disturbances, tangential holes were observed 
here and there in the tissue of the pistil as in that of the stamens. They 
were partly produced by the loosening of the cells from one another, but 
also by the tearing of the cells themselves. The number and size of the 
holes in the tissue increased towards the bottom of the pubescent pistil, the 
hairs of which, poor in contents, showed a browning of the walls. Here 
the tissue at the base of the pistil widened into five diverging, bluntly conical 



521 



parenchyma groups, arranged with tlieir tips toward the centre, as the point 
of transition into the five carpels. Each of these displayed an epidermal 
covering and a parenchymatous inner Hesh. In the cross-section shown 
in Fig. 104, through the receptacle of the apple we see that the future flesh 
is already traversed by numerous, regularly arranged vascular bundles (g). 
The receptacle, covered with a firm epidermis (c), extends, toward the inner 
side, into five anchor-like branches (a). These are the five ovaries into 
which the pistil has widened. On their reflexed edges, which in the cross- 
section look like the flukes of an anchor (r), the seed-primordia are formed 



je^r 




Fig. 104. Cross-section thio«gh a young receptacle of the apple injured by frost. 

in the under part of the receptacle and get their nutrition through the vascu- 
lar bundles (gc). The seed cavities (sf) and the cavity left free in the 
centre (h) because the edges of the ovaries have not united, are lined with 
regular epidermis (e). The cells of the epidermis of the axillary side (br), 
as also within the fruit cup, are found to be richest in contents and, there- 
fore, most deeply browned, while the central, at first meristematic part of 
each ovary is only slightly discolored. 

A splitting of the tissue manifesting itself in the appearance of tan- 
gential holes (/), due to the separation of the collenchymatous layers (c) 



522 



from the inner flesh of the fruit (m) may be seen in the transitional zone 
from pistil to ovaries, even with a low magnification. It should be empha- 
sized that in thiS; as in the stamens, a tearing of the cells (c) actually takes 
place, while in the coarser tissues only the usual separation of the different 
cell layers is formed. These mechanical (listurl)ances which, as we shall 
see later, are so imjiortant in the vegetative organs, have a lesser influence 

in the blossoming organs. The 
inflorescences die because of 
the chemical change in the 
cell contents and drop more 
quickly if the tissue splits at 
the same time. The experi- 
mental results correspond to 
the phenomena after natural 
spring frosts. 

The dependence of the 
susceptibility upon the consti- 
tution of the cell sap may be 
perceived from the adjoining 
illustration of a young apple 
blossom severely frosted (Fig. 
105 ). The shading, carried out 
only on one side in this and 
other drawings, holds good 
naturally for both halves. All 
the shaded parts indicate tis- 
sues with intercellular spaces, 
which clearly contain air. At 
r sugar may be proved by the 
glvcerin reaction. The crosses 
indicate the regions wdiere 
metabolism has already ad- 
vanced so far that abundant 
calcium oxalate is deposited. 
The rings (/) are intended to 
indicate the different places 
turned brown by frost ; all the 
younger, inner parts, rich in 
cvtoplasm, have remained 
healthy; the dark line is a vascular bundle. 

Here we should mention only supplementarily the fact that, besides the 
acute affects of cold already described, chronic disturbances in the life of 
the blossoms also occur which concern only the retarding of the normal life 
processes. The best known example might well be the suppression of the 
opening of the blossoms in Crocus vermis and Tulipa Gesnertana. Because 




Fis. lor,. 



Primordia of an apple flower bud 
injured by frost. 



523 

of the low temperature, no sufficiently strong growth of the inner side of 
the perianth leaves takes place, so that the bending out of these leaves and, 
therefore, blossoming is suppressed. The blossoms of Ornithogalum 
uuihcllatuin, Colchlcnm autumnale, Adonis vernalis and others, react simi- 
larly but more v\eakly. The processes in Mimosa pndica, Oxalis acetosella, 
etc., prove that even green leaves act thermostatically because of the influ- 
ence of lower temperatures. Material on this subject may also be found in 
the later sections which treat of the mechanical effects of frost. 

The Rust Ring.s in Fruit. 

The so-called rust rings appear as the result of slight injuries from 
frost in young fruits. By this are understood various formations of cork in 
the skin of the fruit, spreading, especially in the pomaceous fruits, in ring- 
like zones. In many varieties the appearance of cork-color etchings is a 
very normal process. Our Reinettes. for example, often possess star-like, 
small rusty spots. The so-called "netted Reinettes" have linear cork trac- 
ings on the outer skin of the fruit and often such cork formations obtain 
a surface-like extent, as, for example, in the French Reinettes, Parker's 
gray pippin, in the gray autumn butter pear, the medlar, etc. This condi- 
tion is morbid only when the phenomenon is very extensive in some years 
(for example, 1900) on many fruit varieties whicli otherwise remain smooth 
and when the formation of the cork covers the greater part of the fruit. 
The initial stages are found in early youth. It is evident after the appear- 
ance of very late May frosts that the contents of some groups of epidermal 
cells turn brown and the cells begin to die. Beneath such places plate cork 
is formed, and the dying epidermis becomes somewhat convex. During 
the swelling of the young, green fruit, the formation of cork advances 
further into the fruit flesh, producing considerable groups of parallel rows 
of cells arranged perpendicular to the upper surface. In a special case 
observed in "Amanli's butter pear" these cells, arranged in rows, appeared 
to the same extent as those in the epidermal cells ; they were found actually 
suberized, however, only in the peripheral layers while the light-colored, 
thick walls of the more deeply lying cells gave a cellulose reaction. The 
greater the new formation, the more the overlying, dying cell layers are 
separated and the outer surface of the fruit becomes rough and scaly. 

In flask-shaped pears the pouchy part of the fruit, bearing the blossom 
end, often appears to have rusty grayish scales, while the half toward the 
stem is smooth, and green. In other cases, a broad, cork-colored band is 
seen near the blossom end, etc. At times with this splitting of the waxy 
covering and dying of the epidermal cells is connected the development of 
the newly produced underlying tissue into stone cells. These appear later in 
circular aggregations on the outer surface of the fruit, so that the conditions 
are produced which we have described as "Lithiasis" (p. 170). ("Diel's 
butter pear," "Good Louise of Avranches"). Since such changes are usually 



524 

found on one side the growth of this cork-color side, containing the stone 
cells, is often retarded, thus producing deformed fruit. 

After I had succeeded in causing a splitting of the cuticle in tough 
leaves by the action of artificial frost, I did not hesitate to trace the injuries 
in the wax coat of young fruit to frost action, more particularly the forma- 
tion of such "rust rings" as had been observed only in years with late frosts. 
The pears, which are susceptible to frost, sufifer most abundantly and 
greatly, in fact usually on one side and at a certain height on the tree. 

The Behaviok of Oi.dkr Foliage With Acute Frost Action. 

During frost, changes in the chlorophyll grains are noticeable inasmuch 
as they usually round up into lumps in the cells which have become poor in 
sap. A chemical change of the chlorophyll coloring matter, due to the frost 
alone, is not assumed by the majority of investigators, so far as found in 
statements concerning frozen chlorophyll solutions. Wiesner founcP no 
difference in a chlorophyll solution in olive oil exposed to a temperature of 
30 degrees C. below zero. On the other hand Kunisch- states that the 
alcoholic extract of chlorophyll from hyacinth leaves, frozen at 7 degrees 
below zero, was found to differ from that of leaves which had not been 
frozen. Often dull whitish spots are found in frozen leaves which can 
arise from ice accumulations crystallized out into the intercellular spaces. 
Hoffmann found in Ceratonia, Laurus and Camphora, a vesicular raising 
of the epidermis and called it a "frost blister-'. In heavy frost, the leaves 
which have been frozen through become as brittle as glass and transparent. 
When such leaves are thawed, the change in color depends upon whether 
the protoplasm of the cells has been killed or not. If it is dead, it becomes 
permeable to acids in the cell ; these penetrate to the chlorophyll grains, and 
cause their decomposition (the formation of chlorophyllan) : the cytoplasm 
turns brown ; the cell sap exudes rapidly; the leaf dries into a brittle, brown 
mass. Goppert*, who describes the various colorations of foliage leaves, 
also mentions an extremely strong weedy smell in frozen plants. In ferns 
the odor peculiar to the whole family is retained in frozen and dried speci- 
mens in an unusual intensity. In artificially frozen branches of the sweet 
cherry I noticed a decided odor of bitter almond. These phenomena are the 
result of the chemical changes which make themselves felt immediately 
and strongly during thawing. Fliickiger'^ has observed a different eft'ect in 
the frozen leaves of the cherry laurel. During distillation, these gave off 
an oil differing from that of the fresh leaves and no prussic acid, while 
leaves covered with ice, but not frozen, gave both substances under normal 
conditions. 



1 Wiesner, Die natiirlichen Erscheinungen zum Schutze des Chlorophylls, etc. 
Festschrift d. k. k. zoolog.-bot. Ges. zvi Wien 1876, p. 23. 

2 Kunisch, H., tjber die todliehe Wirkung- niedei'er Temperaturen auf die 
Pflanzen. Inauguraldissertation. Breslau 1880. 

3 Kunisch, loc. cit. p. 22. 

4 Goppert, tJber Einwirkung des Frostes auf die Gewachse. Sitzungsb. d. 
Schles. Ges. f. vaterl. Kultur 1874; cit. Bot. Z. 1875, p. 609. 

5 The effect of intense cold on cherry-laurel; cit. Bot. Centralbl. 1880, p. 887. 



525 

It is important to refer here to the behavior of the mineral substances 
in leaves killed by frost, because we thus obtain an insight into the loss in 
substance caused by the destruction of the foliage in spring frosts. 

Schroeder's' analyses of red beech foliage which a May frost had killed 
and which, four weeks later, was examined in the dried condition, gave the 
following: In the frozen foliage, the whole nitrogen content (3.56 per 
cent.) of the fresh May leaves is found, while in the autumnal leaves, only 
about 1.33 per cent, remains, so that, therefore, almost three times as much 
nitrogen is lost for the plant from the loss of the May foliage as in that of 
the autumnal falling of the leaves. The dry substance gives 3.01 per cent, 
ash. Of this ash, 22 per cent, was phosphoric acid, i. e., as much as fresh 
May leaves, while the July leaves possess only 5 per cent. In May leaves 
about 30 per cent, of potassium was present normally ; in frozen ones, how- 
ever, only 5 per cent. Naturally very little calcium was present in the 
young foliage (6.78 per cent, in healthy foliage, 4.70 per cent, in frozen 
foliage) ; while the vegetating July leaves possessed three times as much 
(20.34 per cent.) the dead November leaves actually exhibited 37.60 per 
cent. 

In opposition to the opinion that foliage killed by spring frosts remains 
hanging on the trees, which thus gives its valuable mineral elements time 
to wander back into the trunk, reference should be made to Ramann's inves- 
tigations-. He proved that the foliage of the oak, spruce and fir, killed by 
cold, at first possessed the same composition as fresh foliage, when analyzed 
before a rain, but, during the rain, it underwent a very considerable change. 
Ramann found that, within ^2 hours, water withdrew not less than 19.219 
per cent, of the whole ash of red beech leaves and actually 26.46 per cent, of 
the oak. This easy diffusibility of the ash elements should not be considered 
to be the result of later decomposition, as is proved by the fact that the 
greater amount had been leached out in the first 24 hours'; viz., in the beech 
15.42 per cent.; in the oak, 19.66 per cent. These latter amounts gave in 
pure ash 11. 15 per cent, and of extraction for the trunk, 14.18 per cent, 
for the oak. 

The amount to which loss of the foliage injures the main body is shown 
in another difi:"erent work by .Schroeder' on "The migration of nitrogen and 
mineral elements during the first development of the spring growth." The 
exhaustion of phosphoric acid in the trunk during the production of the 
young growth is the greatest, namely, 46 per cent. ; then follows potassium, 
2,2 per cent, of which is used up ; nitrogen and magnesium are removed from 
the trunk up to possibly 26 per cent. Before the end of this period, 12 per 
cent, calcium and 84 per cent, of the initial amount of silicic acid are added 
and replace the loss. Of the whole amount of nitrogen, potassium and 



1 Schroeder. Untersuchung erfrorenen Buchenlaubes. Forstchemische u. pflan- 
zenphysiologische Untersuchungen. Part 1, 1878, Dresden, p. 87. 

2 Ramann, Aschenanalysen erfrorener Blatter und Triebe. Bot. Centralbl. 
1880, p. 1274. 

3 loc. cit. p. 83. 



526 

phosphoric acid wandering into the young growth, possibly one-fifth comes 
from the trunk, and four-fifths from the root and soil. These figures favor 
the theory that the root-body, to a still higher degree than the trunk organs, 
gives up its reserve provision of nitrogen, phosphoric acid and potassium. 

Deficient Greening of Younger Leaves. 

A special form of the efifect of lower temperatures on the coloring of 
plant bodies is the remaining yellow of grozving organs due to the lack of 
temperatures necessary for turning green. Elving"^ found that etiolin was 
formed at temperatures which were still too low for the formation of 
chlorophyll in spindling seedlings, which, exposed for a short time to the 
light, became yellower than those left in the dark. When plants are uncov- 
ered in the early spring, numerous examples are found in which the etiolated 
shoots which had been produced under the cover, in spite of the at times 
abundant illumination, generally do not lose their yellow color or lose it 
only slowly and irregularly in spots. The most abundant examples were 
furnished by garden hyacinths. If these are uncovered too early in the 
spring and frost surprises the young leaf cones which are not yet green the 
leaves develop later a normal color but their young tips remain white or 
yellow. 

In the parts which appear yellow, we usually find the chloroplasts 
formed and arranged normally, i. e., along the free lying parts of the cell 
walls or those bordering intercellular passages (epistrophe), but the color- 
ing matter is only a more or less intensive yellow. In this stage, all possible 
transitions, up to the complete absence of the grains in the wholly bleached 
tip of the leaf, are found ; these are not. however, conditions due to disso- 
lution but are arrestment formations. In the whitest parts of the meso- 
phyll. the cells are filled with a watery cell sap which is traversed by 
cytoplasmic cords, without the deposition of any chlorophyll bodies in the 
cytoplasmic wall layer. In other cells of the yellowish parts, the differenti- 
ation of the contents extends to the primordia of the chloroplasts, but these 
appear more whitish, more tender, we might say, and at times, cloudier, 
less dense and less sharply defined. Normally formed, intensively green 
chloroplasts are finally found in the parts of the leaves which have grown 
out of the soil after frost action. At times the lack of green is connected 
with the presence of red coloring matter. Charguerard- furnishes an 
example ; he observed in Phalaris arundinacea picta, that the young leaf tips, 
with their well-known white stripes, appeared reddened by frost. The rose 
red coloring disappeared with warm weather. Schell" confirms the appear- 
ance of the red coloration with cold. In the spring he placed plants with 
red-colored, young leaves under three different temperatures and observed 
that the specimens kept in a room at 15 degrees C. became green within 



1 Arbeiten d. Bot. Instituts zu Wurzburg, Vol. II, Part 3; cit. Bot. Centralbl. 
1880, p. 835. 

- Revue liorticole, Paris 1874, p. 249. 

y Botanischer .Jahresbericht 1S7C, p. 717. 



52? 

i8 hours, while those kept at 8.5 degrees C. turned green only after 5 days. 
The plants left out of doors, with a maximum temperature of about 4 
degrees C. became green only after 20 days when the temperature of the air 
had risen. These observations favor my theory, that the red coloring is 
conditioned by the preponderance of a process of oxidation, connected with 
the action of light, over the process of assimilation. With equal amounts 
of light, a rise in temperature so increases assimilation that the process of 
turning green preponderates. 

To avoid a fixation of the morbid yellowish appearance of leaf tips, 
Ideached by frost, it is advisable to remove the winter co\'ering gradually, 
or, for the first few days, to spread a light layer of brush over the plants. 

Defoliation Duf. to Frost. 

The sudden falling of the foliage during and after the ai)i)earance of 
the first autumnal frost is only one form of the autumnal defoliation which 
should be designated death from senility (in contrast to the cases already 
described of abnormal defoliation after excessive heat, drought, lack of 
light, excess of moisture and other causes, producing a sudden loss of func- 
tion of the organ). The leaf has simply lived out its life. A normal death of 
this kind has the least disadvantageous results for the trunk which remains 
alive. From the senile leaf apparatus many plastic as well as important 
mineral substances gradually wander back into the trunk and are used again 
in the following period of growth. The retention of abundant amounts of 
organic structural substances and the leaching of easily soluble nutritive 
substances by rain are very disadAantageous in leaves which die in a juven- 
ile stage, since these are thus lost to the trunk. But both processes have 
but little significance when the leaves die of old age. In this case, as has 
recently been emphasized repeatedly by B. Schultze\ the assimilation of 
carbon dioxid may well be proved, up to the last moment, even if naturally 
with weakened power. Through the preponderance of the processes of 
decay over those of construction the leaf's supply of easily soluble proteins 
is especially impoverished, \\ith the increasing thickening and calcification 
of the membranes, the conducting of new nutritive substances becomes 
constantly more difticult, so that the demonstrable reduction- of nitrogen, 
phosphoric acid and potassium thus becomes explicable, even if no consid- 
erable process of retrogression is accepted. 

After all that has been said in earlier sections on the infiuence of 
position, soil constitution and w^eather, it is not necessary to emphasize here 
the fact that the life period of the leaves can be proved to be very difl^erent 
for the same species and that in this frost also acts on leaves which vary 



1 Schultze, B., Studien liber die Stoffwandlung-en der Blatter von Acer Negundo 
L., 76 Versammlung d. Ges. Deutsch. Naturf. ; cit. Centraltal. f. Ag-rikulturchemie 
1906, p. 35. 

- Fruwirth, C. and ZieLstoff, W., Die herbstliche RUckwanderung von Stoffen 
l)ei der Hopfenpflanze. Landw. Versuchsstat. 1901; cit. Bot„ Jahresb. 1901. Part 
2, p. 161. 



528 

greatly in age. Accordingly the process of leaf fall is not always the same. 
The most usual case consists in the formation of a tissue zone at the base of 
the leaf which is a characteristic abscission layer. We repeat here the 
illustration of the autumnal abscission layer in the leaf of Acsculus Hippo-, 
castamim (cf. Fig. io6). The illustration gives a section made longitudin- 
ally through the joint at the base of the petiole, a is the bark parenchyma of 
the branch; b, the layer of plate-cork cells which remains when the petiole 
has fallen and thus forms a protection for the bark tissue ; c indicates the 
cells at the base of the petiole which at e pass over into the firmer paren- 
chyma of the broadened bases of the petioles, provided with abundant accu- 
mulations of calcium oxalate. Between c and e takes place the process of 
separation, since at d the cells round off and begin to separate from one 
another. If now the leverage of the leaf, moved by the wind, makes itself 
felt, the petioles break off at the loosened cell layer. 




Fig. 10(). Autumnul abscis.sion layer of a horse chestnut leaf. 
(After Dobner-Nobbe.) 

The riper the leaf is at the time of the final autumnal frost, the more 
easily it falls ; on this account, the old leaves of the branch are found to be 
the first ones broken off by the wind in the autumn. The greater the life 
energy and the quantity of plastic material, the more resistent the youthful 
leaf seems to frosts which are not killing frosts. 

If killing degrees of frost occur in the autumn at a time when the leaf 
has not yet sufficiently matured its abscission layer, i. e., the tree is still far 
distant from its dormant period, then the dead foliage remains on the 
branches over winter (beech and oak). The beeches in w^iich the foliage 
remains hanging often leaf out later in the spring than do normally matured 
specimens^. 

At the time of the first night frost, it is found in the early morning, if 

the frost still lies on the ground and even in windless weather, that, as soon 

as the sun comes up, the simple leaves of the trees break oft' and the leaflets 

of composite leaves fall from the common spindle, v. Mohl- found in such 

1 dc Candolle, A., in Centralbl. f. Agrikulturchemie 187'J, I, p. 159. 
:; Bot. Zeitung- 1860, p. 16. 



529 

cases that the leaf scars of the fallen leaves, or those just about to be 
loosened, were covered, in a number of plants, by a thin layer of ice. Paul- 
ownia, for example, exhibited an especially thick ice crust. Often the 
leaves were still connected with their scar only by the ice crystals. These 
ice crystals had been formed in the abscission layer of the leaves. The 
columnal structure of the crystals, their cloudiness, produced above the 
vascular bundles by little air bubbles, and their arrangement, ending sharply 
with the boundary of the leaf scar, favor the view that no considerable 
masses of cell sap, which had possibly flowed out. have been frozen but that 
small particles of water pass through the cell walls exactly at the place 
where they are observed and are there stiffened to ice. 

The formation of ice may often occur very early and thereby cause, 
when thawing", the fall of leaves wdiich otherwise would have remained for 
some time on the tree and may even still be green. Besides this action of 
the ice lamellae, a premature autumnal defoliation may set in because the 
leaf is partially or entirely frozen; it, therefore, suddenly becomes function- 
less and is then ])ushed off. 

In autumnal defoliation the loosening of the leaf always takes place in 
the abscission layer which, according to Wiesner's observations\ does not 
always arise from a secondary meristem but is often found also as a rem- 
nant of the primary meristem. In other cases of leaf-fall the process of 
disarticulation can take place in different tissues. 

If the process of disarticulation within the layer of separation be con- 
sidered in general, the following modifications will be found, according to 
Wiesner-. So strong an osmotic pressure can be produced in the cells of 
the abscission layer that the tissues separate from one another, leaving 
smooth surfaces. This we find in defoliation which is the result of excess 
of water even where this excess arises from abundant watering after a long 
period of dryness. The phenomena of the dropping of the leaves of 
Azaleas, Ericas and New Holland plants, so well known to gardeners, after 
the drying of the root ball, belong here, as does also summer defoliation 
with the occurrence of rains after a long drought. 

According to Wiesner, in autumnal defoliation the macerating action 
of organic acids comes especially under consideration. He assumes that 
the surfaces of separation, in death from frost, as a result, have an acid 
reaction, and explains this by the fact that the frost kills the cytoplasm, 
thereby making it permeable to the acids which occur in the cell content and 
then act on the membranes. Oxalic acid may play a great part in this. 
The above-named investigator laid the stems of various plants in a 2.5 
per cent, solution of oxalic acid and found that the leaves had loosened 
within a few days. The stems of plants which form abscission layers at 
the internodes also disarticulated within a short time. 



1 Wiesner, Julius, Tiber Frostlaubfall nebst Bemerkung-en iiber die Mechanilt 
tier Blattablosunpr. Ber. d. D. Bot. Ges. 1905, Part 1, p. 49. 
- loc. cit. p. 54. 



530 

If llie leaf surface is injured by frost, but tlie part of the leaf lying 
below the abscission layer, i. e., the leaf stump, remains alive, the frozen 
part of the leaf will dry up, but the leaf base will be found intact and turgid. 
Between the leaf base and the dried part differences in tension must arise 
which lead to the loosening of the leaf body. 

Experiments made by Prunet^ show how quickly the parts injured by 
frost have dried up. A frozen vine branch with four leaves placed in water, 
evaporated 475 mgr. of water within two hours. In this, its loss in weight 
amounted to 14.46 per cent. Under the same conditions a similar branch, 
not injured by the cold, evaporated only 132 mgr. of water and, because of 
the absorption of water which had taken place simultaneously, increased its 
weight by 0.26 per cent. 

Wiesner has also shown experimentally how, in plants which retain 
their frozen foliage for some time, often for the winter, this may occasion- 
ally be based on a rapid drying. He took branches of Ligustrum ovalifoHnni 
with frozen leaves and placed them in a warm room in such a way that the 
sprouts could constantly soak up water. After 6 to 12 days, these dropped 
their leaves while the leaves of shoots not provided with water remained 
firmly attached. In cases occurring out of doors, where the dead foliage 
remains in place on the branches, the separation takes place only after the 
destruction of the tissue. The moldering of the membranes within the 
abscission layer will gradually advance so that the wind or some other 
mechanical cause finally brings about the breaking off of the leaf. In these 
moldering processes micro-organisms will doubtless cooperate. 

From what has been said, it is clear that the mechanics of separation 
in the autumnal senile defoliation, as well as in that due to frost, can often 
differ even in the same individual, according to the age of the leaves and 
the existing accessory circumstances. In many plants (grapes), besides 
the loosening of the w^hole leaf from the axis, the loosening of the leaf 
blade from the petiole also occurs. In other disturbances also, this region 
is especially susceptible and at times manifests its similarity to the base of 
the petiole through a similar discoloration. For example, in poplars, it can 
be observed that in the autumn the base and tip of the petiole become red 
while the remainder is yellow. 

The difference in the time when these processes set in in different indi- 
viduals, and in the same individual at different heights of the various 
branches, is connected with the physiological age of each leaf. The younger 
this is, the later it falls from the branch, under otherwise equal conditions, 
as Dingier- has determined, by pruning experiments. He observed a 
greater power of resistance in the young leaves, especially to autumn frosts. 
The young leaves of Carpinus Betidus did not freeze during frost periods, 



1 Prunet, A., Sur les modifications de I'absorption et de la transpiration, qui 
surviennent dans les plantes atteintes par la g-elee. Compt. Rend. d. I'Acad. des 
Sciences 1892, II, p, 964. 

2 Dingier, Hermann, Versuche und Gedanken zum herbstlichen Laubfall. Ber. 
d. D. Bot. Ges. 1905. Part 9, p. 463. 



531 

lasting all day, but older ones were affected and fnially died. I found 
similar conditions in plane trees in which the age of the tree made itself felt 
in the same way. In street trees, young specimens had been planted be- 
tween the older trees. Although they did not stand under the protection of 
the older trees, they still retained their considerably stronger foliage when 
most of that of the older trees lay on the ground. 

Behavior of Beet and Cabrage Plants in Frost. 

In storing sugar beets the loss of sugar, which occurs in the heaps 
because of the respiration of the beet body, can be decreased only by the 
lowest possible temperature'. In sugar beets which have been frozen, a 
raising of the sugar content was actually found when the water was frozen 
out. This has been reckoned by Ninger to be 0.39 per cent-. 

The new formation of saccharose which takes place during the process 
of freezing is no greater than the amount destroyed. Also the amount of 
nitrogenous substances and the proportion of proteins to non-proteins re- 
mains unchanged. So soon, however, as thawing begins, the latter appear 
to be increased at the expense of the former. The elements of the raw 
fibers (cellulose and related substances) become more soluble in acids and 
alkalis and in part also more soluble in water because of the freezing"'. In 
this an increase of non-sugar substances is produced in the sap. I observed 
in frozen beets partial swellings of the membranes which might be ex- 
plained as a visible expression of the chemical changes in the cellulose. 
.Strohmer and Stift found a striking increase in the acid content. 

The large sugar content, produced by the loss of water, and the conse- 
quently more concentrated cell sap will, however, retard the actual freezing 
of the beet body. Besides this, in the storage piles, the outer, frozen tubers 
will protect the inner ones from freezing. Miiller-Thurgau has referred to 
this especially and Mez* has explained it by the fact that the conversion 
of the cell saj) into a solid aggregate condition preserves the energy still 
present in the cell from too rapid dispersal. The conduction of warmth 
takes place much more slowly in ice than in water, where the warmth is 
distributed by radiation. 

The statements of market gardeners that brown cabbage (Brassica 
oleracea acephala) obtains its desired sweetness only after frost, may find 
adequate explanation in the accumulation of .sugar due to the low tempera- 
ture. According to the analyses made by Marker and Pagel'', an amount 
of sap equal to 68.66 per cent, of the remnants of the plant may be pressed 



1 Heintz, Atnuing- der Riibenwuizeln. Zeitschrift d. Ver. f. d. Rlibenzuckerin- 
dustrie d. deutsch. Reiches 1873, v. XXIII; cit. Bot. Jahresb., I, p. 358. 

2 Bot. Jahresber. 1880, p. 665. 

3 Strohmer, F. und Stift, A., tlber den Einfluss des Gefrierens auf die Zusam- 
mensetzung- der Zuckerriibenwurzel. Osterr-Ung. Z. f. Zuclverindustrie und Land- 
wirtsch. 1904. Part 6. 

4 Mez, Carl, Neue I^nter.suchungen liber das Erfrieren eisbestandiger Pflanzen. 
Sond. Flora od. Allgem. Bot. Zeit. 1905, p. 109. 

5 Marker und Pa.ge1, tjber den Einfluss des Frostes auf Kohlpflanzen. Bieder- 
mann's Centralbl. 1877, v. XI, p. 263-66. 



532 

out from frozen cabbage plants while the same pressure gave only /-i per 
cent, sap in examples which had not been frozen. lOO ccm. of sap con- 
tained in 

frozen plants not frozen plants 

Dry substance 7.96 g 4.04 g 

Raw Ash ' 1.63 " 0.97 " 

Grape Sugar 4.17 " 1.41 

Dextrin (?) 0.80 " 0.58 " 

Nitrogenous substances 0.80 " 0.51 

Extractive substances free from nitrogen 0.50 " 0.54 

This shows that the soluble elements in the sap have undergone a con- 
siderable increase and that, in this, grape sugar is especially concerned. 
Here, therefore, just as great a formation of sugar has been found as in 
the potato; Schmidt' states this to be 21.85 per cent. 

Frost Blisters. 

Frost blisters are of less significance agriculturally but certainly worthy 
of consideration scientifically because of the production of mechanical dis- 
turbances in the tissues inside the organs which remain alive. These mani- 
fest themselves in the appearance of usually small, blister-like places in the 
epidermis and at times also in the sub-epidermal layers which are raised 
from the thin-walled parenchyma of the leaf flesh or the tougher paren- 
chyma of the leaf veins. Instead of an extensive description, we will 
reproduce in Fig. 107 a cross-section- of the frost blister on an apple leaf. 
O indicates the upper side, U, the under side. M is the mid-rib, j> a larger 
lateral vein. 

In the mid-rib. the crescent-like wood body, with its numerous ducts 
{(j), forms the chief part. On the upper side adjoins a thin walled layer 
of parenchyma (m) free from chlorophyll, corresponding to the pith body 
of the axis. This parenchyma layer is covered by thick-walled collen- 
chymatous cells (c) ; these develop more abundantly, the larger the vein is. 
The collenchyma extends as firm wedges somewhat above the part of the 
leaf surface which consists only of leaf flesh. The leaf flesh shows the 
usual division into palisade parenchyma {p) and spongy parenchyma {sp). 
Of these layers, containing chlorophyll, the palisade parenchyma does not 
extend over the vascular bundles on the upper side but spreads out on both 
sides like a keel so that it terminates in a short cell layer {hr). This be- 
comes one layered, between the collenchyma and the parenchyma of the 
body of the vein. The spongy parenchyma, on the other hand, extends on 
the under side o\ er the body of the vascular bundle and forms the bark part 
of the vein in which, as in the bark of the branch, may be found oxalate 
crystals (o) arranged in crescent-like rows. The epidermis {e) covers 
the whole leaf uniformlv. 



1 After Ritthuusen; cf. "Der Landwirt" 1875, p. 501. 

- Sorauer, P. Frostblatjen an BUltteni. Z. f. Pflanzenkrankh. l'J02, p. 44. 



533 

The mechanic.nl action of frost is sliown Iiere in the form typical for 
the majority of our plants since, on the upper side of the leaf, the collen- 
chyma tissue above the vascular bundle of the large vein is raised up from 
the parenchyma, thereby forming an opening (/'). On the under side of 
the leaf, the spongy parenchyma has been freed from the bark part of the 
vein on the scarps of the very prominent body of the vein so that cavities 
(h), containing air, are produced on both sides of the rib. The formation 
of the cavities is explained by the fact that the youthful, still hyponastic 
leaf, the edges of which are up-curled, from the action of frost, contracts 
at both sides of the mid-rib from above downward, as well as tangentially. 
If the up-curled, trough- like leaf contracts, the curling must become greater, 
i. e., the distension of the under side becomes stronger. This manifests 
itself in a pulling toward the raised edges (see the direction of the arrow in 




Fig". 107. Cross-section through a frost boil in .in npplo leaf. 



the ilkistration ). The tension is the greatest at the scarp of the vein and 
can, at times, lead to a splitting of the epidermis (c'). 

If thawing now takes place, the result of the action of the frost is the 
overlengthening of the tissue which has been strained, for the tissues are 
indeed distensible but not completely elastic. They do not regain their 
former size and arrangement. The lower epidermis, which has been most 
strained, elongates and no longer exercises on the spongy parenchyma, 
lying beneath it, the previous amount of pressure. The pressure in the 
epidermis is broken and the spongy parenchyma responds at once, elongat- 
ing into pouches. If, at the time of the greatest tension, the epidermis is 
torn apart, the over-elongated edges of the tear (e') form a crater-like 
opening toward which grow out the rows (/) of the spongy parenchyma 
which develop into threads. 



534 

We find further investigations of frost blisters in a work by NoackV, who 
comes to the conclusion that they are produced "because water from the 
cells is pressed into the intercellular spaces and there turns to ice so soon 
as the temperature falls to a certain degree below the freezing point, differ- 
ing for the different varieties of plants." The formation of ice crystals 
was found by Noack to be strongest at the place where later the separation 
of the epidermis becomes visible. We owe a recent study to Soleredef-. 
He observed in the leaves of Buxus the same hairy outgrowth of the meso- 
phyll cell rows that I had found in apples, cherries, apricots and have illus- 
trated in Fig. 107. Solereder has proved experimentally that this elongation 
of the cells of the leaf flesh is a secondary phenomenon occurring with an 
abundant supply of water. He removed the under side of the leaf and set 
the plants in a moist place. Cuticular warts were then produced on the cell 
membranes, similar to those which we have illustrated by the woolly stripes 
in apple cores (p. 324) and have observed also in the frost blisters of cherry 
leaves. The beginning of this hair-like elongation of the cells is found in 
the sheath of the vascular bundles, i. e., in places where the cork disease of 
the cactus (p. 429, Fig. 71) may be recognized as the initial point of the 
diseased processes of elongation. We find in this an experimental proof of 
our theory that the disturbances named may be traced back to excess of 
moisture. 

We will discuss later, in connection with other mechanical disturbances 
due to frost, the question whether the frost blisters were produced by the 
crystallized ice, or formed previously by a difl^erence in tension due to the 
cold, thus ofi^ering for the formation of ice the most convenient places of 
deposit. We will for the present only emphasize the fact that the holes in 
the tissue pictured in the apple leaf (on the upper side of the veins and 
below on their scarps) are a typical frost peculiarity found frequently in 
very dilferent leaves which also remain green during the winter. 

Comb-like Splitting of the Leaves. 

In some years with late frosts the phenomenon, in which the otherwise 
continuous surfaces of tree leaves often appear slit and thereby approach 
those forms which are characterized as "folia laciniata" may be found not 
infrequently. While, however, in commercial varieties, the slit leaf form 
is a condition fixed in the developmental course of the individual and may 
be transmitted by grafting, the slitting due to frost forms a transitory stage 
which, even in the same summer, may return to the normal leaf form. 

I had opportunity in the spring of 1903 to observe the very frequent 
occurrence of the phenomenon in Aescidus Hippocastanum^. The structure 
shown in Fig. 108 was restricted to the lowermost leaves of the shoot, i. e.. 



1 Noack, Fr., tjber Frostblasen und ihre Entstehung. Z. f. Pflanzenkrankh. 
190R. p. 29. 

2 Solereder, H., tJber Frostblasen und Frostflecken an Blattern. Centralbl. f. 
Bakteriol. 2d Section, v. XII, 1904, No. 6-8. 

3 Sorauer, P., Kammartige KastanienbUltter, Z. f. Pflanzenkrankh. 1903, p. 214. 



535 

those appearing first from the hud. C)n the same leaflet could he found all 
transitions from deep incisions extending as far as the mid-rih (Fig. io8f) 
to the normal undivided leaf surface (Fig. io8/). It was observed on those 
transitional ijlaces that exactly in the middle line of each intercostal field 
and spread between two parallel, lateral veins, occurred a lighter colored, 
transparent stripe along which the tissue was broken in places. (Fig. 108(7.) 
The edge of such a ruptured place, like the edge of the individual feathery 




Fig-. 108. Horse chestnut leaf, injured in the bud by frost, and toi-n, like the teeth 
of a eomli, during unfolding'. 



tips of the slits, often shows a some\^•hat yellowish, harder line, sometimes 
appearing a little callused. This callused edge consisted of plate cork cells, 
to which, on the outside, were not infrequently attached rags of dead meso- 
phyll cells. It is evident from this that the comb-like incisions had not been 
formed in the bud, but were produced later. 

In the above mentioned, transparent lines, of which the first are broken 
only in places, the mesophyll is found to be dead on the uninjured part. 
The cell content was still abundantly present but brown and collected in 



536 

balls. The vascular Inindles showed the well-known frost browning. The 
fact that exactly the midline of the intercostal fields is always the part 
injured by frost is explained by the peculiar folding of the leaf surfaces 
in the bud primordia. 

I found the same phenomena also in Acer Pscudoplatanus and some 
other thick-leaved varieties of maple ; in these, however, only in the form 
of irregular perforations. Laubert' observed a feathery slitting of the 
leaves of the birch and the white beech. Thomas- explains the slit condi- 
tion of the leaves chiefly as a result of the action of the wind. It has been 
known, ever since A. Braun and Caspary, that chestnut leaves can be per- 
forated and in places slit by the mutual rubbing of the leaf surfaces, but 
the phenomenon here described has nothing to do with the action of the 
wind. 1 have found the beginnings of the split leaf condition in little trees 
which had been brought into the house soon after the action of the frost". 

The Heaving of Seeds. 

Aside from the injuries which hardy herbaceous plants can sufifer from 
lying too long under a snow cover, because they are often suffocated, we 
have to take into consideration another phenomenon which becomes espe- 
cially disadvantageous for grains, i. e., the heaving of young plants. 

It is only the soils which contain a great deal of water which exhibit 
the heaving of seed by frost. After unsettled winter weather, when sharp 
frosts suddenly follow wet days in the early spring, a number of young 
[jlants with exposed roots are not infrequently found on the upper surface 
of the held. A part of the roots, to be sure, still touch the earth with their 
tips, and eke out for the seedlings a pitiful existence, while other rootlets, 
perfectly free, with torn tips, are exposed to drying wind and sun. The 
explanation of this occurrence is very pertinent here. The heavy soil 
retains large quantities of water; this freezes into long, needle-like crystals 
and thereby raises the upper layers of the soil, together with the young seed. 
If a part of the fine roots have already reached a considerable depth they 
are torn loose. In the subsequent thawing the soil can settle back in place, 
but not so the young plants. A repetition of the process finally brings the 
above result and may cause considerable loss if help is not brought quickly. 
The help consists mainly in the use of a heavy roller at a time when the 
soil has already dried to some extent. By pressing the sprouted seed, the 
lower nodes of the stem obtain protection and dampness enough to put out 
new adventitious roots and in this way gradually overcome the injury to 
the organs which hold them fast and nourish them. Especially in grain 
plants rolling acts beneficially and in damp spring weather strong blades 
will grow from plants which have thus been drawn out of the soil. 



1 Laubert, R. Regelwidrige Kastenienblatter. Gartenflora, 52. Jahrg., 1903, 
Oktober. 

- Tliomas, Fr. Die meteorologischen Ursachen der Schlitzbliitterigkeit von 
Aesculus Hippocastanum. Mitt. d. Thuring. Bot. Ver. 1904, Part 19, p. 10. 

3 cf. Z. f. PHanzenkrankh. 1905, p. 234, Note. 



537 

Draina^^e will naturally act as a precautionary method. A loosening 
of moor soil by raking it o\er with sand may also be proved favorable. 
Kiihn', in this connection, found that drill cultivation was also effective 
since all seeds were thus hoed in again. Between these seeds are produced 
thereby "small grooves into which the moisture chiefly passes and thus, 
under the conditions cited, an upraising of the soil is observed in the spaces 
between the ])lant rows, while the plant rows themselves remain untouched." 
Hedwig- recommends early sowing in order to obtain as abundant deep 
growing roots as possil)le and thereby to secure the plants more firmly in 
the soil. 

Ekkert'' recommends a surface sowing, but chiefly the growing of 
strong plants. In favoring this surface sowing, Ekkert seems to have been 
influenced by the statements of Count Pinto-Mettkau, who says that only 
seeds which lie deep are hea\ed out of the s<m1 and. in this are torn at the 
base of the primary internode, i. e., at the part of the stem which is strongly 
elongated only in deep sowing and which raises the node of the plant toward 
the upper surface of the soil. This theory is shared also by Breymann'. 
Ekkert's investigations on the firmness and elasticity of this lowest part of 
the stem and of the roots favor the view that, in this heaving from the soil, 
the roots are torn sooner than the internodes. With surface sowing, it is 
possible that only the roots will be torn and the superficially lying grain, 
therefore, also carried up so that it will still remain as a possible retainer of 
reserve substances for the injured plant. The injury would conser^uently 
be less and more easily overcome with the additional help of a rapidh- 
effective spring fertilizing. 

Johannes rye has been recommended as a resistant variety. In wheat. 
a Russian variety, Urtoba zvhcat, is found to be especially resistant. How- 
ever, neither variety nor depth of sowing will determine this in the end, but 
chiefly the constitution of the soil and its power to retain water become of 
especial importance. 

In young tree plantations, the heaving of the seed occurs also with 
black frost. The seedlings of pines and oaks, provided with strong, long 
tap roots, did not suffer, but those of the superficially rooting spruce and 
hemlock and, among many deciduous trees, the black alder in boggy soils, 
do so. 

Internal Injuries in Young Grain. 

As yet, no attention has been paid to the fact that grain plants suffer 
internal injuries from black frosts, even if they are not heaved from the 
soil. These injuries, with continued wet weather, form convenient centres 

for the attack of parasitic fungi. Besides the common black fungi, we will 

ik 

1 Krankheiten der Kulturpflanzen 1S59, p. 11. 

- cit. in Goppeit, Warmeentwicklung-, etc., p. 236. 

3 Ekkert, tjbei- Keimung, Uestockung und Bewurzelung der Getreidearten, etc. 
Inauguraldissertation, Leipzig, 1874; cit. in Biedermann's Centralbl. 1875, p. 204. 

4 Dber das Auswintern des Weizens, des Rapses und des Rotklees. Bieder- 
mann's Centralbl. 1'. Agrikulturchemie 1881, p. 829. 



538 

also find the snow mold, the breaker of the rye blade, the killer of the wheat 
blade, etc., all of which cause the further destruction of the plant. Besides 
the browning of the vascular bundles in the plant nodes, the frost injuries, 
predisposing the plant to fungous diseases, consist especially of a blister-like 
raising of the outer membrane in definite places of the grain leaf. Such 
blisters are found even in very young leaves in the bud as is shown in the 
adjoining Fig. 109. We find that the outermost edge (B) of the young leaf 
is so injured by frost that the cell contents have become brown and rounded, 
the cells have collapsed and, therefore, die in a short time (gs). On the 







Fig. 109. Young rye leaf, injured by frost, with eruptions on the epidermis. 

other hand, the part of the leaf spirally rolled up (A) appears perfectly 
fresh and capable of further development. 

The leaf, of which the outer side, while in the bud, is curved outward 
like a bow, possesses a main vascular bundle (g) above which are deposited 
hard bast cords (&) on the outside, and also weaker bundles (g'), ramifying 
in the middle, broader region of the leaf, which nourish the increased meso- 
phyll. Among the changes in tissue produced by frost, the one should be 
emphasized in which the enlarged cells (r) become noticeable after the 
thawing. These are radially elongated and in part irregularly pulled out of 
shape (^), with greatly bowed walls. This condition proves the presence 



539 

of abnormal tension conditions. To these should be ascribed also the very 
conspicuous phenomenon of the production of holes (/) regularly arranged. 
The holes are produced by the blister-like upraising of the epidermis from 
the real leaf flesh, usually on the upper side, between the rows of stomata 
(sp). The under, or outer side, of the leaf shows only scattered holes of 
small extent. The tangential elongation of some of the epidermal cells, 
noticeable at times (cp and ec) offers an important proof of the production 
of these holes. The epidermal arch has become larger than it was before 
the action of the frost ; this elongation is the result of the stretching of single 
cells. Besides this upraising of the leaf, a radial splitting in the vascular 
bundle indicated at /' is very characteristic of frost injury; this becomes of 
especial importance in the axillary body. 

To distinguish the formation of holes, due to the action of frost, from 
the tearing of the tissue, due to senility, we give in Fig. no the cross-section 
of the first sheath -like leaf of a rye plant, the inner tissue of which, in the 




Fig-. 110. Natural cavitie.s in the sheath-like rye leaf, formed during- growth. 



course of normal development, splits at death. The holes (h), produced 
thereby, are always tangential. 

Internal Injuries in the Graix Stalk. 

More important, however, than the leaf injuries is the effect of frost in 
the stalk itself. \\'e usually have no suspicion of this, since, to the naked 
eye, no change is noticeable in the plant. Fig. iii illustrates a lower node 
of rye injured by frost. 

The tissue of the stalk (H) is firmly enclosed by the sheath (Sch), the 
outer epidermis of which is indicated by c, the inner by e' while e" indicates 
the upper epidermal cells of the stalk. The browning of the ducts in the 
different bundles, which occurs in all frost injuries, is indicated at u and u' 
where the narrower spiral ducts between the wide annular ducts seem the 
most injured. At br are found aggregations of brown parenchyma cells 
in the sheath; at br' the same in the stalk itself. At v and v' are shown 
brown groups of cells in the sheath and in the stalk, the walls of which are 
very strongly sxvollcn up so that the whole cell seems converted into a uni- 



540 




Fig. 111. (Upper figure) Leaf node from a rye plant, injured by frost. 

Fig. 112 and 113. (Lower figures) Swelling of the membranes on the leaf sheaths 

of a rye blade injured by frost. 



541 

form yellow, gum-like mass. At other places (r) the parenchyma in the 
inner part of the sheath is torn or is filled with peripheral holes, due to the 
raising of the epidermis. Elongated cells occur near such holes or often 
instead of them, and point to the fact that, in freezing, the stalk is most 
often contracted tangentially, thus pulling the epidermis out of shape. 
Because the epidermis is not so elastic as the rest of the bark tissue, it 
remains permanently elongated as the result of this tension. When the 
frost ceases, it is raised in places (/ and /'), or perforated, and its pressure 
on the underlying parenchyma decreases, causing the parenchyma cells to 
elongate into pouches (rd). The elongated cells, usually under the outer 
epidermis (c), but more rarely on the inner side (-'), often possess strongly 
curved, or stretched walls. 

These conditions are magnified and illustrated in Figs. 112 and 113. 
Here the processes of wall swelling appear to be so great that one is able to 
distinguish only indistinctly the limits of the individual cells; some cell 
lumina disappear almost entirely (t'). The loosening of the epidermal 
pressure, connected in the above case with the phenomena of swelling, has 
caused the over-elongation of the underlying tissue and the formation of 
considerable groups of bent, abnormally enlarged cells in some places (rd) 
and isolated ones (-c) in others. 

Finally, the phenomenon of splitting within and around the vascular 
bundles is most worthy of consideration. In the vascular bundles the split- 
ting takes place usually in a radial direction (Fig. iii^) ; in fact in such a 
way that the more tender tissue between the two wide ducts is torn. The 
part surrounding the vascular bundles can be so greatly torn (r) that the 
bundle projects into the- cavity. This phenomenon gives the impression 
that the parenchyma had contracted so strongly, as a result of the frost 
action, that it is torn off from the resisting, firm bundles. In case such 
dift'erences of tension make themselves felt less extremely, the parenchyma 
near the bundles is only greatly strained, causing a subseciuent production 
of enlarged cells with cur\ed walls (^')- 

Injuries to the vascular bundles, for which the vascular elements must 
certainly compensate by their conductive activity, are of great importance 
lo the life of the plant. This explains the developmental retarding of plants 
injured by frost. .Such plants, even without the cooperation of the para- 
sitic organisms, which especially seek out weak seed, furnish less straw and 
especially badly nourished grain. z\s a rule, however, there is an addi- 
tional parasitic injury due to rust, black fungi and other leaf and beard 
inhabitants. The development of the stalk is irregular since all plants in 
the field never suft'er e(|ually strongly ; besides the individual differences in 
power of resistance, the inequality of the soil sometimes favors the frosts 
and sometimes gives protection from them. The more injured specimens 
stand under the shade and pressure of vigorously growing ones. A defi- 
ciency of light and air and the increase of moisture among the oppressed 
plants favor the infection and extensive distribution of the fungi. 



542 
Lodging of the Stalk. 

The frost injuries above described in stalks show different secondary 
phenomena, according to the place where the frost acted most intensively. 
The most common case is where, with late frost, the base of the stalk is 
attacked. Usually these injuries occur in definite centres in the fields be- 
cause the cold air accumulates in low-lying hollows. Here also most of the 
moisture from atmospheric precipitations collects so that parasitic infection 
is added to the frost disturbances. The base of the stalk begins to molder 
and the stalk itself falls over. Many of the cases of lodging of the stalks, 
ascribed to Leptosphaeria and Ophiobolus, are found to be combination 
phenomena of which frost is the primary cause. 

There are, however, other cases, in which the stalks do not break at the 
base but at different heights. The phenomenon does not always occur in 
definite centres in the field but may also be found in bands and manifesting 
itself in such a way that healthy and diseased stalks stand side by side. 
.Such cases not infrequently cause disputes since they bear a great resem- 
blance to injuries due to hail. Reparation is refused by the Hail Insurance 
Companies since it is not possible to prove where the hailstones have hit. 

In the basal lodging of the stalk, its ground tissue is found to be brown 
and the shoot almost entirely dead. It is often, indeed, soft and always 
infested by fungi ; also bacteria, mites and anguilla in continued dampness. 
When the break occurs higher in the stalk, the ground tissue seems firm 
and green and the shoots die only in places, often without infection by fungi. 
Most frequently the broken place in the stalk is found at the second or third 
internode above the surface of the soil and is characterized sometimes as a 
one-sided, sometimes as a circular brown zone, the coloration of which in- 
creases in intensity towards the next higher node. Accordingly the part of 
a stalk, lying close below a node seems to be the most susceptible place. 
Nevertheless, the node adjoining the upper side of the deep brown tissue 
can frequently lead to a secondary upbending of the fallen stalk so that it 
finally stands upright again beyond the bent place. But the heads of such 
plants are weak and imperfect ; the roots appear healthy, the brown part 
almost always without any fungous growth. 

The Condition of Sterile Heads. 

A disease which apparently has the least connection with frost injuries 
is the condition of sterile heads, as met with in Fig. 114, A and B. As yet 
I have found the phenomenon only in rye and will describe only a special 
case which I had opportunity to observe in June, 1900^ Here the stalks 
were mostly of a normal size and vigorous growth, but the uppermost mem- 
ber, or the one next below it, had pale yellow spots. Later these became 
straw-colored to a brownish-vellovv, often with darker edges, which en- 



1 Sorauer, P. tjber Fro.st))eschadungen am Getreide und damit in Verbiudung 
stehende Pilzkrankheitcn. I^andw. Jahrbticher 1903, p. 1. 



543 



larged to a band girdling 
the stalk. In other cases 
the stalk was perfectly 
healthy up to its upper- 
most internodes. 

The uppermost leaf 
sheaths and leaves, how- 
ever, had straw-colored 
specks (Fig. 114 B t) 
or pits. The upper part, 
together with the base 
of the spindle of the 
head, was a reddish 
straw color. The spindle 
itself \A'as brownish, dot- 
ted with salmon spots, 
entirely bare at the base 
(k) but, further up, 
covered with paper}' 
glumes, at first thread- 
like but later becoming 
somewhat broader {sp). 
The tip of the head 
could de^•elop fully, as 
shown in Fig. 114, B, 
and the nearer this green 
tip the thread-like, white 
glumes stand, the coarser 
and larger they become 
and the more their con- 
stitution approaches the 
normal condition. At 
times groups are found 
with green fleshy glumes 
on the part of the 
spindle which remains 
bare (Fig. 114, B a). 

Fig. 114 A repro- 
duces a case in which 
the lower glumes are 
normal and green. The 
upper ones are normal 
m size and form but 
have a reddish, straw- 
colored appearance ; the 




Fig-. 114. Difterent forms of dterilitv, 



544 

spindle is naked between the tip and the base. In more extreme cases 
of injury, in place of the head, only a bare, brown membraned spindle 
with salmon-colored spots remains. The salmon-colored points are the 
places of attachment of the grains and colored by luxuriantly developed 
tufts of fungi. 

In almost all cases of sterile-head condition, the axis is bent in the 
form of a crook (Fig. 114 B a) by the drying of the bare part of the spindle. 
In the examples pictured, it is clearly seen that the sterile head condition 
owes its production to locally effective causes. When these phenomena 
were studied on a field where especially many plants had suft'ered from 
sterile-head condition, it was noticed that the zone of injury could be found 
at approximately equal distances from the soil. Therefore, the injurious 
cause must be found in a layer of air which is present exclusively at a 
certain distance above the soil. The rye plants, affected in different stages 




Fig-. 115. Cross-section through the internode of the head of a rye blade suffering 

from sterility. 



of individual development, are injured differently, according to the extent 
to which they have penetrated into this injurious air layer. 

It is thus evident that sometimes the lower part of the head will become 
bare, sometimes the upper part. In the best developed, tallest plants, in 
which the heads, standing on the longest stalks, are already above the 
injurious air layer, the heads remain perfectly uninjured; only the upper- 
most section of the stalk has a pale band. 

In discussing the cause of this sterile-head condition, the supposition 
would seem most pertinent, that the disease is caused by the fungus, recog- 
nizable on the band and especially on the spindle of the head and appearing 
in salmon-colored ridges at the places of attachment of the blossoms. 

This hypothesis, however, is erroneous since even greater injuries to 
the spindle have been observed when the presence of the fungus could not 
be proved. On this account, this fungus, which belongs to the genus Acre- 



545 

monium, is to be considered as a secondary infection, just like the almost 
omnipresent Cladosporium. 

If now the injured spindle is examined in those places which Acre- 
monium has not infested, the pictures reproduced in Figs. 115 and 116 are 
obtained. Fig. 115 represents a cross-section through an internode ; Fig. 
116, one through a node of the head spindle; c indicates the epidermis; h, 
its hairs; <j, a healthy vascular bundle; g', a bundle with shrivelled brown 
walls ; (js, vascular bundle sheath ; b, bast parenchyma ; luj, wood part of 
the bundle ; 11, deep brown tissue between the two large ducts, which is very 
sensitive and is proved to be injured first by various causes; pr, healthy 
prosenchyma cells; pr', the same with healthy walls but brown, filled lumina; 







pr 



Fig-. 116. Cross-section through the node of the sterile stalk. 

pr", prosenchyma possessing colorless cell cavities but deeply browned walls ; 
V, parenchyma cells in the epidermis and bark tissue with yellow, thickly 
swollen walls and barely distinguishable lumina; ;:', elongated cells near the 
gum-like, swollen tissue centres; bl, basal part of a head which separates 
here from the node. 

Thus, in the bare parts of the head spindle, all those forms of injury 
are found, which are noticeable in the lower nodes of all frost-injured 
grains, only, instead of clefts in the tissue, swellings of the membrane pre- 
dominate. These are especially extensive at the places of attachment of 
the heads because much more abundant parenchyma tissue, i. e., tissue more 
susceptible to frost, is present there. And such gum-like, swollen tissue 
centres lie deep in the interstices of the spindle. By means of this ana- 



546 

tomical condition, tlit sterile heads, due to frost, are diiifercntiated from the 
similar, well-known injuries to the heads due to thrips, the suction-points of 
which remain superficial. At any rate, thrips are found not infrequently on 
heads injured by frost since these animals seek out weakened organs; but 
their usual small number and the change in the tissue of the spindle leaves 
no doubt that the infection is secondary. 

The fact that I have succeeded in producing, by artificial frost, all the 
injuries to leaf, stalk and head described here is decisive. All the different 
forms of shrivelling of the grain could also be produced experimentally. 

The condition of sterile heads due to frost occurs only in different 
years and not extensively except in definite localities. 

The thought that only certain parts of the stalk are injured by frost, as 
must be presupposed in the condition of sterile heads, at first seems strange, 
but one at once becomes more familiar with it if the affected regions are 
examined. Either the basal part of the head, which appeared last from the 
sheath, together with the adjoining upper part of stalk, is affected, or the 
part of the internode lying directly under the node, showing the frost band. 
The parts named, however, are the most tender and susceptible of the 
whole stalk and we find analogous phenomena also in dicotyledonous plants 
where the stems of the blossoms and fruit are injured and blackened only 
directly at the base of the blossom, while the older part remains healthy. 

It could not be determined by observation what atmospheric conditions 
must exist in order to produce interrupted heads or bands on the stalks, 
because attention was not called to the phenomenon until some time after 
the action of the frost. Some of the meteorologists consulted incline to the 
opinion that dew plays a part in this. 

Frosty nights in May are usually windless and the injury to the plants 
results from the cooling down of the organs by their radiation of heat. The 
upper surface of the soil itself cannot be cooled down very greatly in a 
close standing rye field since it retains its daily warmth for some time 
through the mantle formed by the air, found between the stalks, which can 
be moved with difficulty. The greatest amount of cooling through radiation 
can take place only in the upper part of the stalks. These, however, are 
covered by the evening dew. The morning wind rises suddenly with the 
sunrise and starts a rapid evaporation of the dew. The cold, due to this 
evaporation, can fall even below the freezing point. The places with a 
lesser amount of dew, the parts which are protected by other stalks lying 
in front of them, thus remain protected from this cooling down to the freez- 
ing point. The distribution of the dew on the same part of the plant, 
however, will differ since the places which, through bending, are inclined 
more horizontally than others, will retain even larger amounts of dew. 
Among the organs exposed to the freezing temperature, however, only 
especially tender ones will suffer. This explains the fact that on a head 
isolated places alone can be injured. In addition to the fact that the base 
of the head is pro^'ed to be the most injured, the circumstance that the 



547 

frost does not injure the organs richest in cytoplasm first but, under similar 
conditions, those poorest in it is a further explanation. 

The grains at the base of the head are, however, the most poorly nour- 
ished and poorest in cytoplasm, as may be recognized in any healthy head 
of grain. 

As a result of a conversation with the director of the German Naval 
Observatory, Admiral Herz, the latter sent me later, most kindly, the fol- 
lowing explanation : "In a stand of plants, whether high or low, the soil 
is, on the one hand, protected against the nocturnal radiation, while, on 
the other hand, this radiation takes place strongly from the surface of the 
plantation and. because of poor warmth conductivity, is very efifective. 
However, the air, cooled near the leaves, sifts down through the plantation 
just as on declivities it sinks into depressions in the soil. It is, therefore, 
very conceivable that the lowest air temperatures begin somewhat below 
the upper surface of such a plantation, especially if its denseness increases 
towards the ground, or if the tips are protected from too extensive cooling 
by a light wind." 

The way in which the processes actually take place out of doors which 
bring about the injurious cooling of different horizontal air layers at con- 
siderable distances from the upper surface of the soil is left for further 
observation. The experiment, in which a wooden cylinder, with a mantel 
containing a cold mixture was set over the upper part of the blossoming 
rye stalk, proves that the condition of sterile heads is produced by such 
action of the frost. Because of the impossibility of rapidly mixing the 
individual horizontal air layers in the freezing cylinder it was proved that 
only a definite zone was so cooled down that it brought about the described 
injury to the heads. 

We conclude, for example, from Nordlinger's observation^ that the 
injuries take place in forest trees and indicate the existence of a layer of 
air, which causes death from frost above the warm surface of the soil. 
Nordlinger found in June. 1862, in the Hohenheimer Oberen forest young 
shoots of willow, oak and aspen frozen at the base of the petioles, and in 
August, 1883, several kinds of willow, especially Salix fragilis, when there 
had been no night frost. 

Phenomena of Movement Due to Frost. 

In many plants survi\'ing frost peculiar [phenomena of movement result 
from freezing, which disappear again with thawing. Goppert- mentions 
Linneus' observation that the leaves of the milkweed {Euphorbia Lathyris) 
bend their tips backward until the leaf lies against the petiole. The leaves 
of the wall-flower (Cheranthus Cheiri) look wilted in the frozen condition 
and often bent, but after thawing they regain their former consistency and 
position. 



1 Nordlinger, H., Lehiburh des P'ovst.schutzes. Berlin, P. Parey 1884, p. 347. 
- Warmeentwicklung- in den Pflanzen, p. 12. 



548 

Wittrock^ perceived in the phenomena of movement a protection 
against the cold of winter. For example, the evergreen root-leaves of 
numerous plants bend backward and downward so that at last the outermost 
part of the under leaf surface seems pressed against the soil ; in summer 
they have a slanting position. This is especially clearly noticeable in Hypo- 
chocris maculata L., Gcum urhanum L.. CcrcfoUum sativum L., and others. 
Also a few early spring plants like Ranunculus Picaria L. behave similarly. 
Hartig recognized in these phenomena rather a wUting of the parts of the 
plant, resulting from the limi)ness of the cells, from which the water has 
been frozen out into the intercellular spaces. Since the freezing of the 
water in the various parts of the organ will differ according to the age and 
maturity of the tissue, the dift'erence in the movement, due to frost, might 
be explained in this way. 

Such phenomena of movement, however, seem in no way connected 
with the formation of ice and are only extreme cases of thermonastic reac- 
tion which, as Pfeffer- states, are expressed in the nocturnal drooping of 
the blossoms, leaves and shoots. Vochting' observed in Mimulus Tilinfjii 
Rgl. that shoots of a certain age grow upward in the spring with a high 
temperature or maintain a horizontal direction with a low one, while in 
case they have developed an upright position, they reassume the horizontal 
one. Light and humidity have no influence. He believes that with con- 
tinued low temperatures the ])lant might develop only creeping shoots on 
which blossoms are never produced. This sensitiveness ceases in the blos- 
soms which are termed psycho-clinic. Lidforss"* concludes from numerous 
observations on Holosteum, Lamium, Veronica, etc., with which klinostatic 
experiments were also made, that in such movements not only changes in 
turgor are concerned but actually the effects of stimulation. With a higher 
temperature the petioles are negatively geotropic, but in temperatures below 
6 degrees, they are dia-geotropic and epinastic. Here, however, the light 
acts as a modifier since, with its exclusion, the petioles, in spite of the lower 
temperature, are no longer dia-geotropic but negatively geotropic. 

The movements of the peduncles of Anemone nemorosa are, on the 
other hand, of a purely thermonastic nature. They curl downward with a 
lower temperature but stand upright with a higher one. 

In petioles and leaf surfaces, the resumption of a horizontal position is 
often noticed, or a bending backward below the horizontal plane on taller, 
upright axes. In this, however, we wish to emphasize the fact that the 
movements take place usually in the points and are not always of the same 
nature in the same plant. It can happen that, in compound leaves, some of 
the leaflets turn upward while the majority bend downward ; that, therefore, 



1 Bot. Ges. zu Stockholm. Sitz. v. 24. Oktob. 1883; cit. Bot. Centralbl. 18S3, 
No. 50, p. 350. 

2 Pfeffer. Pflanzenphvsiolosie, 2d edition, v. II (1904), p. 495. 

3 Bot. Jahresb. 1898, I, p. 582. 

4 Lidforss, Bengt. tjber den Geotropismus einiger Friihjahrspflanzen. Jahrb. 1'. 
wiss. Bot., V. 38, 1902, p. 343. (Z. f. Pflanzenkrankh. 1903, p. 277.) 



549 

sometimes the morphologic upper side, sometimes the under side of the joint 
cushion is shortened. Among the changes appearing especially clearly with 
ice formation, the curling of the leaf surfaces should be emphasized. An 
example very easily observed is furnished by our Rhododendron. Harsh- 
berger^ describes a case of Rhododendron maximum in which the petioles 
sank to 70 degrees while the edges of the leaf curled backward so much 
that the upper surface appeared convex. If the plants were brought into a 
warm room, their leaves resumed their normal position after 5 minutes. 
Hartig ascribes this process to a peculiar irritability of the cytoplasm while 
I assume differences of tension between the differently constructed layers 
of tissue. 

In many woody plants a movement of the branches and twigs propor- 
tionate to the degree of cold is found. According to Caspary- Acer 
ncgundo and Pterocarya cancasica direct their branches upward, while 
Larix, Piniis Strohus and Tilia parvifoUa lower their branches. Aesculus 
Hippocastanum and Aesculus Hippocastanum rubra, as well as Carpinus 
Betidus lower their branches with a slight degree of frost and raise them 
again when the cold becomes greater. Simultaneotis with this raising and 
lowering is a lateral motion, in some varieties toward the right, in others 
toward the left. In Cornus sanguinea Frank-'' found that the one to three 
year old branchlets became wavy and twisted above each other. Most of the 
twistings were found to be clearly directed toward one and the same point 
of the compass so that Frank concluded it was the effect of a current of 
cold air coming from a certain direction. 

As stated above, we might seek the causes for the movements in leaves 
and petioles, as well as in branches, in differences of tension which takes 
place, partly because of changes in turgidity, partly from unequal contrac- 
tion of different tissue forms within the same organs due to the appearance 
of cold. 

An experiment which I carried out with Aesculus Hippocastanum 
proves that an increase of turgidity of the parenchymatous tissues in "leaf 
wilting due to frost" can, under certain circumstances, again cause the stif- 
fening of those leaves. 

A three year old potted specimen was put into a warm place in Febru- 
ary. It developed vejy vigorously until the middle of March so that the 
terminal shoot, 14 cm. long, had developed six leaves. The largest leaflet 
of the two youngest leaves was 2.5 cm. long and in the lower, older leaves 
the length of the petiole was from 5 to 9 cm. 

The plant was put out of doors on March 14th. The following night 
the temperature fell to 2.5 degrees C. below zero, and the next morning a 
sharp bending or breaking of the petioles was noticed on four of the older 



1 Harshberger, John, Thermotrophic movements of the leaves of Rhododen- 
dron maximum; cit. Bot. Jahiesb. 1899, 11, p. 141. 

- Report of the International Horticultural Exhibition, etc., I^ondon ISfifi; cit. 
in Nordlinger, Forstbotanik, I, p. 201. 

■■ Frank, A. B., Krankhoiten d. Pflanzen. Breslau 1895, v. 1, p. 187. 



550 

leaves, approximately in the centre or somewhat below it. The places of 
breaking were flatly compressed and began at once to become flabby. The 
tips of the leaflets, which otherwise did not appear wilted, were flabby on 
the broken leaves and began to turn brown. 

Since such a breaking of the petioles had not been observed previously, 
this plant was again placed out of doors on the night of the 2i-22d of 
March. The temperature fell to 7 degrees C. below zero and the next 
morning the leaflets of all the leaves hung downward at a sharp angle. The 
youngest leaves showed this phenomenon the least of all. Even in a still 
frozen condition, no part of the young growth seemed brittle, or of a glassy 
consistency, so that any conclusion as to a formation of ice crusts in the 
tissue was scarcely possible. The leaflets were soft and flabby, of a grayish 
green color, and the petioles, as long as the plant stood out of doors, curved 
downward sharply but were not broken. The breaking took place only 
after some hours indoors and, indeed, as in the first observed injury, near 
the middle of the petiole. This place shrivelled at once and turned brown. 
At the same time all the leaflets, with the exception of the youngest, began 
to turn black, starting at their place of insertion, and the tips curled upward 
and became dry. 

The processes of breaking must be traced back to a lever action con- 
nected with decreased turgidity, for, as soon as some of the leaves, broken 
by weak frost action, were removed and placed in water, they lost the ap- 
pearance of wilting in spite of the broken place, and a great stiffness of the 
tissues set in. To be sure, the leaflets retained their downward inclination, 
peculiar to the youthful stage, but their intercostal fields curved outward 
strongly between the veins and their side edges began to turn under. 

The wilting and breaking is explained by the inner phenomenon of 
cleavage in the pith body of the petioles. In the chestnut the petiole has a 
structure similar to the trunk, inasmuch as it possesses a closed circle of 
vascular bundles which completely and uniformly surrounds the broad, 
colorless pith disc and passes over into it in a gradation similar to the pith 
crown. Even after the weakest frost action it was noticed that the pith 
body of the petioles which had not yet broken, contained holes, usually of a 
radial arrangement, and seemed ready to .break, because of the limpness of 
the corresponding place. This occurred near the base of the petiole. Be- 
cause the vascular body, running through the centre of the pith disc and 
consisting of two or three bundles, remained intact and the tears in the pith 
parenchyma ran radially to all sides, a peculiar star-like figure of cleavage 
was sometimes found. In the leaves, which had been broken only after a 
second, stronger frost action, the splitting of the pith disc at times was so 
strong that the central vascular bundle cord was connected with the peri- 
pheral vascular bundles only by a slender parenchyma strip and all the rest 
of the pith disc had been dissolved. The holes were continued, not infre- 
quently, in or between the peripheral vascular bundles and formed splits 
which extended to the edge. Within these occurred also tangential out- 



551 



pusliings of two to four outer rollenchyma layers, with a tender, inner tissue. 
The latter tissue was seen to be rich in chlorophyll and at times, in fact, 
showed still definite chlorophyll grains. Similar disturbances could be 
proved also in the midribs of leaves more greatly injured. 

Here the phenomena of browning were first perceived in the walls of 
the ducts and then in the various peripheral groups of the bark. 

In wilting out of doors, due to frost, naturally such an increased supply 
of water, as obtained here in the experiment by placing the cut leaves in 
water, cannot take place and, on this account, the wilted organs retained 
for some time, or permanently, the wilted condititjn, especially if a splitting 
of the tissue and changes in the ducts reduced the conductivity. This can 
take place diiTerently not only in 
the different varieties and individu- 
als, but even in the different 
branches of the same specimen. 
An example of this was furnished 
by an elm which stood in a pot 
and in winter was brought into the 
hothouse for forcing. The little 
tree, which had been exposed to 
a frosty night at only i degree C. 
below zero, had developed two 
forked apical branches which ap- 
proximately corresponded to one 
another in length, leaf number and 
size. In this frosty night, however, 
only scattered leaves of one shoot 
had begun to wilt but did not 
change color. The relaxed organs 
did not recover after several da}/h 
retention in the warm room but 
showed no advance of the wilting. 

It is clear from this that wilting due to frost is a very local phenomenon 
not directly connected with the upward forcing of water by the root. 

In the phenomenon of the movement of twigs the different kinds of 
movement may be easily explained if the structure of the individual branches 
is more closely observed and it is seen how, in the maturing of the annual 
rings, the thin-walled spring wood (Fig. Ii8) constantly changes to a thick- 
walled autumn wood with small lumina. In this connection the studies of 
R. Hartig^ should be compared showing the change from thick-walled, red 
wood to the light, porous strain wood within the same cross-section of a 
spruce branch. In the adjoining Fig. 117 the red wood is found especially 
strongly developed in the first annual periods on the upper side of the 
branch. In later years these showed a sudden change, since rather the 

1 Hartig, R., Holzuntorsiichnng-en. Berlin, Springer, 1901, p. 50. 




Fig-. 117. Cross-section through a spruce 
branch. In the inner part of the wood 
disc the solid red wood is shown on the 
upper side of the branch but in the outer 
annual rings it is seen on the under 
side. (After R. Hartig.) 



552 




Fig-. 118. Red wood from the under side of a spruce branch (Cross-section). The 

uppermost cell row is spring- wood; the lower four rows are red wood with 

larg-e intercellular si)aces (at the left). (After R. Hartig-.) 




Fig-. 119. Cross-section through strain wood on the upper surface of 
a spruce branch. (After R. Hartig.) 



553 

under side of the branch appears dark because of the dense formation of 
red wood. We perceive in the anatomical pictures in Figs. ii8 and 119 
the different structure of the elements of the "red wood" and "strain wood." 

We obtain from R. Hartig reports, well worth considering, as to the 
production of such differences. He states that, for example, in trunks with 
an eccentric growth, the formation of the annual rings is especially strongly 
developed on the branched side. The formation of red wood is proved to 
be often dependent upon the prevalent direction of the wind, since the side 
away from the wind favors red wood formation. If the west wind, for 
example, strikes a spruce constantly, the west side will be strained. The 
east side, toward which the tree is bent, is more strongly pressed and incited 
to a stronger formation of red wood while the windy side, stretched by the 
bending of the trunk, produces strain wood. Every branch will show just 
such differences, for the weight of the needles will bend it downward. Its 
morphologically upper side, therefore, is under a constant strain which 
exercises a stimulus on the cambium. This consequently forms thinner- 
walled; less woody but longer tracheids and these represent the "strain 
wood." 

Besides the action of the wind, the formation of the wood on every 
branch is influenced by its surroundings. Shade from other trees, or prox- 
imity to cliffs or walls, the one-sided effect of greater moisture, partial 
defoliation due to the grazing of animals, or other one-sided changes in the 
nutrition of the branch will call forth a lack of uniformity in the quantity 
and quality of the annual ring. From this it is clear that, in the action of 
cold, the contraction of the tissue must vary greatly and the depression of 
the branches must be very manifold, according to the distribution of strain 
and red wood. Therefore, the observations made by different investigators 
can have no general significance but should only be registered for the 
present as individual cases. 

We will discuss thoroughly the differences due to strain in the section 
on "Internal Cleavage," 

Freezing Back of Older. Branch Tips. 

A freezing back of the branch tips is found in some of our woody 
plants, almost as regularly as defoliation. Mulberry trees, acacias and 
raspberries furnish the commonest examples of this. We owe more exact 
studies on this point to v. MohP, who refers to the different stages in which 
our woody plants are found at the beginning of the winter. 

In many plants the grov.th of the branches continues undisturbed so 
long as the conditions are at all favorable for further development. This 
growth only stands still during the period of cold and, as soon as the tem- 
perature allows, begins again immediately at the point where it stopped in 
the autumn. This is the case in the ivy (Hedera Helix) and the Savin 



1 Bot. Zeitung- 1848, p. 6. 



554 

(Juniperus Sabina). In many trees the developmental period of a brancli 
ends of itself towards the close of summer. In this a terminal bud is 
formed which, the following spring, takes over the direct continuation of 
the branch, as in fruit trees, oaks, ashes, spruces and firs. In our culti- 
vated plants the case often occurs when a second shoot (Johannestrieh) is 
developed in the same year. This not infrequently produces unripe wood 
which freezes easily in winter, while the wood of the spring shoot is always 
completely matured. A third large group drops the tip of the branch all 
at once in the course of the summer while unfolding, where the develop- 
ment is otherwise perfectly normal. The continuation of the branch is 
then taken over in the following year by the uppermost, lateral bud as 
shown in Gymnocladus canadensis and Ailanthus glandulosa. Further 
examples are offered by the linden, the elm, the plane and the hazelnut, 
v. Mohl proved that the trees, the tips of whose twigs almost regularly 
freeze,, belong to this last group. Specimens, for example, in Rome have 
regularly thrown off the tips of their branches in October and thus have 
actually closed their period of growth. This happens in the case of the 
linden. In trees of this group, which are favorites in planting, such a 
normal ending of growth does not take place in the majority of cases. This 
indicates that our summer is too short and too cold for them to reach full 
development. 

Frost, therefore, always attacks immature growth. Here belong 
Robina Pseiidacacia, Gleditschia, Sophora japonica, Broussonetia papy- 
rifera, Morus alba, Salix babylonica and J^itis rinifera. If the twigs are 
to be retained, their premature defoliation would be advisable. Thus, for 
example, according to the observations of Lawrence^ in the winter of 1708- 
1709, of all fruit trees, only the mulberry survived because its leaves had 
been picked for feeding the silk worms some time lie fore the occurrence 
of the cold. 

In our fruit trees, the dying of the branch tips, as a result of the 
occurrence of winter cold, is usually termed tip blight. Not infrequently, 
however, a resulting phenomenon is associated with it, which first makes 
itself felt in summer. If it happens in many branches that only the espe- 
cially delicate basal rings are injured, these branches, as a rule, develop 
further and the blossom buds already formed develop fully. About June, 
however, a yellowing of the foliage appears, a dropping of the fruit already 
set and a drying of the twigs. As a result of the injury to the branch ring, 
the conducting of the nutritive substances is disturbed and the branches 
themselves remain alive only as long as reserve substances are present. 
After these are used up the branch dies. 

In grapevines the case in which the vines freeze back to the old wood 
deserves especial mention. There then develop from the base of the trunk 
uncommonly luxuriant shoots which, it was formerly thought, would be 



1 Goppert, Warmeentwicklung, p. 5. 



555 

sterile in the next year and only bear fruiting wood the year after. Op- 
posed to this theory, the investigations of Miiller-Thurgau^ have shown 
that such wood, even in August of the year of its production, can form 
fruit buds and that the treatment of the vine is to be planned accordingly. 

The Dying of the Cherry Trees Along the Rhine. 

As a special example of the phenomenon previously described, we will 
consider the disease of the sweet cherry in the provinces of St. Goar, St. 
Goarshausen and Unterlahn which has been much discussed since the be- 
ginning of this century. 

According to the material- which 1 obtained from that region, and 
cases which I observed elsewhere, the phenomenon appears as follows : 
a turning yellow of the foliage of some branches, or of the whole crown 
sets in rather suddenly and usually with the appearance of considerable 
gum exudation; the branches, or even the whole trunk, die. Often the 
tips of the branches develop further while the rest remains bare. Micro- 
scopic investigations determine a high degree of gummosis ; gum holes 
can be found even in the youngest shoots. In the wood and in the bark 
body, the phenomena of browning are often found, which we will discuss 
later when describing the action of artificial frost. Indeed these are 
provable often in the apparently healthy shoots, leaves and fruit stems. In 
older trees definite forms of tissue clefting are frequently found which 
correspond with those produced by artificial frosts. Because of this dis- 
covery, I am of the opinion that not only in the "Dying of the Rhenish 
cherry tree," .but also in similar cases which appear often but usually to a 
lesser extent, frost action at the time of the spring growth is to be consid- 
ered as the actual cause. 

Gothe^, who agrees with our theory, describes as follows the weather 
conditions for the localities lying along the Rhine, in the year when the 
disease appeared: "The cherries were already in bloom when on the 22nd 
of March they were surprised by a drop in temperature to 9.7 degrees C. 
below zero. In the course of the spring abnormally strong fluctuations 
took place between great cold and great warmth. I consider such weather 
contrasts to be the cause of the very numerous cases of subsequent disease 
which, in the stone fruits, are almost always connected with strong gum- 
mosis and are accompanied by infection with wound parasites or parasites 
of weakness. Also, for the special case on the Rhine, such a fungus Valsa 
leucostoma was at first made responsible'*. Soon after, however, Wehmer" 



1 Muller-Thurgau, Uber die Fruchtbarkeit der aus den alteren Teilen der Weln- 
stocke hervorgehenden Triebe, sowie der sog. Nebentriebe. Der Weinbau 1882. 
No. 28. 

2 Sorauer, P., Das Kirschbaumsterben am Rhein. D. Landwirtsch. Presse 1900, 
P- 201. , I i i,jii*,J 

3 Gothe, R., Das Absterben der Kirscbenbaume in den Kreisen St. Goar, St. 
Goarshausen u. Unterlahn. D. Landwirtsch. Presse 1899, p. 1111. 

4 Frank, A. B., in D. Landwirtsch. Presse 1899, No. 83, p. 949. 

B Wehmer, Zum Kirschbaumsterben am Rhein. D. Landwirtsch. Presse 1899, 
No. 96. 



556 

drew attention to tlie fact that this fungus, which Frank at first had de- 
scribed as Cytospora ruhcsccns, was not able to produce the disease but 
should be considered as a secondary phenomenon, just like the simultaneous 
occurrence of bacteria. Aderholt^ first cited the experimental proof that 
Valsa is not able to penetrate at once into healthy tissue. This investi- 
gator found, in his artificial freezing experiments, that the co-operation of 
late frosts was unmistakable in the growth of fungus. 

In regard to the above named fungus, Aderholt is of the opinion that 
if the fungus recjuires, for its infection, the injury produced by frost or 
some other good cause, it still is able to strengthen itself later so much that 
it can spread parasitically. This theory agrees perfectly with that of 
Vuillemin- in regard to the cherry disease observed in Lorraine in 1887, 
which bears great similarity to the one here discussed; Coryneum Beijer- 
inckii is named as the cause, and the author associates with it Ascospora 
Bcijcrinckii as the ascospore stage. It would thus seem to be the theory 
of the above investigator that climatic causes have produced the condition 
for the disease but the fungus produced the disease itself. Accordingly, 
in combatting this disease, all wood infested w^ith Valsa or its conidial 
form, the Cytospora, must be carefully destroyed. 

However, we obtain an insight into the real relation of this fungus to 
the disease only from the very recent inoculation experiments which 
Liistner" has carried out. Among others, he took two small cherry trees 
of diiiferent varieties and broke back their crowns. The end broken and 
the piece of the trunk left standing were inoculated with the conidia of the 
fungus and also later painted with water containing them. Since the crown 
did not die back as a result of the breaking, it was later cut ofif and tied on 
to the trunk. By the end of October the fungus, as shown in Fig. 120 at 
the places marked with an A', had spread over the broken and dead end of 
the tip, while the remaining part of the trunk, although inoculated in the 
same way, remained perfectly healthy and continued to grow. The wound 
due to inoculation had healed normally. 

Liistner quotes similar results from Beijerinck and Rant"*, who could 
not produce a gummy exudation on peaches and cherries with Cytospora, 
and report nothing as to the death of the inoculated branches. 

Supported by these experiments and my personal observations, I con- 
sidered not only the disease under discussion but also the others produced 
by varieties of Valsa, or their pycnidial forms, as occurring with the 
co-operation of parasites of weakness, in which only the appearance of 
disease was determined by the fungus. The fungi are able to infest the 



1 Aderhokl, R., tJber das Kirschbaumsterben am Rhein. seine Ursachen un<l 
seine Bekampfung. Arb. d. Biolog. Abt. f. Land- u. Forstw. am Kais. Gesundheit- 
samte. Berlin 1903, P. Parey u. J. Springer, v. Ill, Part 4. 

2 Vuillemin, Paul, Titres et travaux scientifiques. Paris, Typog-raphie, A. Davy 
1890, 4o. 

3 Liistner G., Beobachtungen iiber das rheinische Kirschbaumsterben. Bericht 
d. Kgl. Lehranstalt, fiir Wein-, Obst- und Gartenbau zu Geisenheim a. Rh. f. d. 
Jahr 1905, von Prof. Wortmann. Berlin, Paul Parey 1906, p. 122. 

•* Centralblatt fiir Bakteriologie und Parasitenkunde, I'art II, v. 15, p. 374. 



557 




^^ig. 120. Cherry sapling infected in two places with the conidia of Valsa 
leucostoma. After infection, the top was cut off below the upper wound. At O 
the normally healed wound. At X pycnids of Valsa leucostoma. (After Liistner.) 



558 

branch only when it has become diseased, or at least weakened, as a resuh 
of disturbances in nutrition due to atmospheric or soil conditions. On 
such a foundation no further injury is needed for the penetration of the 
fungi; this can take place also through the lenticels. The disturbance in 
nutrition, which must of necessity exist previous to the infesting by such 
parasites of weakness, is not always necessarily caused by frost. Unsuitable 
habitat and excess of moisture or drought, etc., can just as well give the 
first impetus. Liistner considered the last named factor as the cause of 
weakening in the cherry trees on the Rhine, while I would rather hold to 
the theory that, in the majority of cases, injuries due to frost, and in fact 
those which take place in spring, represent the primary cause. 

Accordingly, I see only a very slight consolation in the careful destruc- 
tion of the parts attacked by fungus. One should not forget especially 
the ubi(|uity of the Cytosporeae and similar groups of fungi. The main 
point is the cultivation of varieties ivhich have adjusted themselves to a 
definite locality. Besides this one should experiment to see whether the 
sensitiveness to frost can be decreased by an addition of calcium to soils 
rich in humus. 

Branch Blight ]n Forest Trees. 

I judge in the same way, as in the dying of the cherry tree, a disease 
which Fuckel has observed in apricots and peaches. A characteristic yel- 
lowing and wilting of the foliage with a subsequent dying of scattered 
branches began in June. Fuckel considers Cytospora rubescens as the cause 
and Falsa prunastri Fr. as the perfect stage. 

Of the better known occurrences of diseases of this character. I will 
add here "the black blight of red beech shoots." According to Willkomm^ 
the cause of the dying of the shoots, which turned black at the base, should 
be sought in a fungus which develops a conidia form like Fusisporium 
candicum Lk. and may be associated with Libertella faginea Desm. The 
perfect stage would accordingly be Quaternaria Perse oonii Tul.- 

The dying of the pyramidal poplars which was found in varying inten- 
sity through northern and central Germany aroused discussion at the begin- 
ning of the 8o's in the last century. A similar occurrence had been 
observed in England between 1820 and 1840'". Younger shoots had brown 
places in the bark under which the wood body also was usually attacked. 
The leaxes became yello^^ ish and limp and the branch died. 

Among the different theories which were brought forward to explain 
the phenomenon, the degeneration of the species through continued sexual 
propagation played a chief role. Although much reference was made, from 
the beginning, to the fact that a late frost might be taken as the cause, 



1 Willkomm, Die mikroskopLschen Feinde des Walde.s, 1S66, Part I, p. 101. 

- Selecta fung. carp. II, p. 105. 

■■ Biolog. Centralbl. XI, 1891, p. 129. 



559 

which in sprinj; had injured the hut httle matured hranches^, the theory 
that a discomycetous fungus Dothiora sphaer aides Fr. produced the dying- 
finally prevailed. In other places a different fungus, Didymosphacria 
populina, was made resi:)onsible for it^. Vuillemin* cites Maminia fimhriata 
in the dying of the twigs of the hornbean and Didymosporium salicinuin 
as the destroyer of willow plantations. Finally we will call attention once 
more to the dying of the red alders described by AppeF as due to Valsa 
oxystoma, which fungus can complete its work of destruction only in speci- 
mens weakened by disturbances in nutrition. 

Freezing of the Spring Growth. 

If late frosts surprise the tree at a time when the leaf buds have began 
to elongate, or have already developed into short shoots, repeated injuries 
and also phenomena of regeneration will then set in. A case which I have 
found frequently in cherries shows the dying of the youngest growing 
l)oint in the opening leaf bud. The injury is not noticeable at first since all 
the leaf buds have remained intact. After some time, however, a pecuhar 
spreading appears, called forth by the turning back of the very turgid 
bracts and the absence of growth excites investigation. Later, sickly, 
lateral shoots appear from the uninjured lateral buds and at times also a 
fasciated growth after such spring injuries. 

I succeeded not long ago in producing the same kind of disturbance 
by the action of artificial frost. Fig. 121 represents a cherry branch in 
which three buds have lost their growing points from frost. The vegeta- 
tive activity, very energetic in the spring, has so made itself felt in the two 
upper buds that the bract-like, early leaves have become larger, a darker 
green and fleshier and have spread out from one another almost hori- 
zontally. At the lowest bud there is a beginning of two lateral compen- 
satory shoots. 

In Fig. 121 B the condition of the bud with a frozen growing point is 
more exactly reproduced. The growing point (a) is blackened and dried 



1 The explanation of this disease as a result of frost has been substantially sup- 
ported by the observations of Count von Schwerin (Gartenflora 1905, Part 5, p. 400). 
He proved, on an Italian trip, that south of the Alps the pyramidal poplars were 
not diseased, 1. e. no degeneration of this tree could be observed in its present home. 
Its death, occurring in bands throug-hout Germany, is explained simply as the result 
of spring" frosts repeatedly occurring at the end of the '70's after long, damp and 
mild autumns. Of the earlier observers Hausknecht (Bot. Ver. f. Gesamtthtiringen; 
cit. Bot. Centralbl. 18S4. p. 2i:^) had already called attention to the fact that the 
dying showed itself almost entirely in the river valleys and depressions, but spared 
higher positions. We find another valuable note by Pertsch in St. Petersburg 
(Deutsche Gartnerzeitung 1884, No. 10). He found on a trip througlv northern, 
western and central Germany that the length of the dead tips became constantly 
shorter, the farther south he went. The fact that Populus pyramidalis is not found 
in St. Petersbui'g, while P. alba, P. iaurifolia, P. suaveolens, P. Balsamea, etc., thrive 
there shows that it is more susceptible to frost than most of the poplars. 

2 Rostrup, Pyramidepoplens Undergang. Tillaeg til Nationaltidende 13. Novem- 
ber 1883. 

3 Vuillemin, P., Remarques etiologiques sur la maladie du Peuplier pyramidal. 
Revue mycol. 1892, p. 22. 

4 Vuillemin, P.. Titres et travaux scientifiques. Paris 1890. 

5 Appel, O., tJber bestandweises Abstcrben von Roterlen. Naturwiss. Z. f. 
Laud- u. Forstw. 1904. 



56o 

and is cut off by a cork layer within the boundaries of the living tissue. In 
the part of the axial cyUnder which has remained alive, however, frost 
action is shown in the form of horizontal splits in the pith (Fig. 121 B, I) 
and a browning which must necessarily retard its functions as a body 
capable of swelling. These are the reasons why the axis does not elongate 
again so quickly. The spiral ducts {(j) which pas-s out into the leaves (bl) 




Fig. mi. A. Branch oi a .sweet cherry. The buds, injured by artificial frost, 

have tliickened and fle.shy scales, enlarged and bent away from one another. 

B. Longitudinal section through an injured bud of the branch. 

also appear greatly browned, but the parenchyma (p) of the bark body is 
but little injured and of unusual tenseness. Traces of starch were found 
here and there at the time of the investigation (June 21). It is clear that 
the almost fleshy bark body contains an excess of water and nutritive sub- 
stances and, accordingly, must take over an increased productivity. The 
greatly increased upward forcing of the water is also to be taken as a 
cause of the position of the bud bract and the bract-like leaves (bs), both 



56i 

of which ha\c become longer lived througli the chlorophyll content of the 
inner tissue layers. 

In occurrences of this kind, frequent in many years in certain locali- 
ties, it is noticed that, as a rule, the tip bud, which has already advanced 
farthest in development, can grow on undisturbed. Then the branches 
have a whip-like appearance, inasmuch as their tips are richly leaved while 
the lower internodes remain bare. Another phenomenon with which I 
became acquainted in older pear shoots consisted in a blackening and dying 
of the basal parts of the young shoots which otherwise still appeared green 
and did not dry up until later. 

Potonie has given special study to the phenomena of the restitution of 
spring shoots lost through frosts Diflferent varieties of trees behave dif- 
ferently. In many varieties lateral shoots grow from the still uninjured 
basal buds of the frozen branch as, for example, in Casfanca sativa Mill, 
and also in varieties of Celtis and Platanus. If the young shoot is entirely 
destroyed, a new foliage growth takes place in many plants by the forma- 
tion of "accessory sprouts." Many tree varieties, especially with increas- 
ing twig nutrition, form not one alone but a succession of buds in the axil 
of a leaf by the sprouting of the inner bud stem called "lower buds." 
These "lower" or "accessory buds" under normal conditions can develop 
only on strong shoots of some trees (Cercis). In disturbances, however, 
as for example, severe pruning, grazing and frost, which destroy the shoot 
jiroduced from the main bud, they also form the compensatory material 
in other trees, as for example, in Calycanthus floridus, Cercis Siliquastruin, 
Ciymnocladus, Liriodendron tulipifera and Robinia Fscudacacia, and de- 
velop as many as four "lower" buds hidden in the base of the petiole. On 
the other hand, compensation can also be secured from their so-called 
"fringing buds" formed the year before. These are the buds in the axils 
of the basal bud bracts which at times succeed in developing regularly as is 
perceived clearly in many varieties of ^^'illow. If the covering formed by 
the union of the two bracts drops off, an axial bud is found, corresponding 
to each half bract and this can form a compensatory branch when the 
main branch is injured. 

In other cases the tree must depend on the dormant buds of the shoots 
of the previous year for compensation, as may be observed especially with 
Rhus, Carya glabra Mill, and Juglans rupestris Engelm, while Carya amara 
Mich, and Pterocarya fraxinifolia Lam. chiefly unfold "lower buds." 
Conifers generally replace the frozen sprouts by the awakening of buds 
dormant up to that time, and also by a new formation of bud primordia in 
otherwise budless leaf axils, especially those of the bracts at the base of the 
annual growth. 

No special limitation in the kind of compensation in frozen shoots of 
diflferent varieties of trees can be made, however, since the strength of the 



1 Potonie, tjber den Ersatz erfrorener Friihlingstriebe durch accessorische 
und andere Sprosse. Sitzungsber. d. bot. Ver. d. Prov. Brandenb. XXII, 1880, p. 81. 



562 

frost injury, on the one hand, and the previous nutrient condition of the 
tree, on the other, together with a greater or lesser ease of adventitious 
bud formation, characteristic of each variety, call forth different compen- 
satory shoots in different cases. The more luxuriantly a variety grows, 
the more it inclines to the formation of "lower buds," as can be observed 
frequently by the breaking of eyes on the main stem. 

In grapevines, regeneration takes place from the lateral buds if frost 
has killed the main ones. This depends greatly on the time of the frost 
action. If the death of the main bud takes place so early in the year that 
it has used but very little reserve material in its elongation, then frequently 
the reserve material still present in the vine is sufficient to strengthen the 
lateral buds so that blossom buds can still be set. If, however, the main 
bud dies from a frost in May, strong shoots can develop, to be sure, from 
the lateral buds, but without setting blossoms. These shoots become fertile 
only in the next year. 

Freezing of Eoots. 

Not infrequently, especially in wet places after open winters, the roots 
of very different woody plants are found to have been frozen while the 
aerial, axillary parts have remained alive. This phenomenon is explained 
by the fact that the wood of the roots is softer and more porous than that 
of the trunk. The softness is due, on the one hand, to the fact that, at the 
time when the cold penetrated deepest into the soil, the growth of the root 
had not entirely stopped ; therefore the frost attacked still young, unthick- 
ened elements. On the other hand, however, the already matured elements 
of the wood body are not so thick-walled as the corresponding parts of the 
aerial, axillary body. This is universally true without taking into consid- 
eration the nutriment and water content of the soil. That the degree of 
luxuriant development will also exert an influence on the sensitiveness to 
frost cannot be denied, but this influence, according to v. Mohl's investiga- 
tions^ manifests itself differently. 

A consideration of the annual range of temperature will give the 
necessary explanation in regard to the first point, the action of the frost 
wave on roots not yet dormant. 

It should be noted in advance that measurements of the tree's tem- 
l)erature prove the dependence of this temperature in the tree top on the 
fluctuation in the atmospheric warmth, while the temperature of the trunk, 
especially at the base and in thick barked varieties, is very considerably 
influenced by the warmth of the soil", since the water, necessarily rising to 



1 V. Mohl, Einige anatomische unci physiologische Bemerkungen liber das Holz 
der Baumwurzeln. Bot. Zeit. 1862, Nos. 29, 33, 34, ff. 

2 Breitenlohner and Boehm (Sitz. d. Kais. Akad. d. Wiss. zu Wein, May 17th, 
1877) found that under usual conditions the temperature of the lower part of the 
stem is entirely influenced by soil temperature, but if transpiration is arrested, the 
temperature of the tree depends entirely on the air temperature. 



563 

make up for the evaporation of the foUage\ has the temperature of the soil 
layers. R. Hartig- furnishes very clear proof of this. The branches were 
removed from one of two similar trees, on which the sun shone, so that in 
the current of evaporation they almost came to a standstill. The ther- 
mometer then proved a temperature of about 10 degrees lower in the tree 
on which the leaves had been left than in that from which the branches 
had been removed. After the removal of the branches of the second 
specimen, its temperature at once increased about 10 degrees. 

Since, in spring, the air body warms up very quickly, it soon increases 
the direct action of the sun's rays on the branches" and keeps them at a 
temperature at which they can grow. The more intense and lasting the 
warmth in the air, the more the cambial ring is stimulated so that its pro- 
duction of new wood and bark elements extends from the crown down- 
ward until, in April and May, it reaches the roots and then finally causes 
the production of a new wood ring. The time of the awakening, the 
thickness of the new wood ring and its maturation differ in different tree 
species. In fact, an individual difference disappears inasmuch as all speci- 
mens are not able every year to produce so much plastic material in the 
tree top that it will suffice for the nutrition of the cambial mantel of the 
roots. It then happens that the thickening ring, in such a lean year, 
extends from the top only to the base of the trunk where it tapers out to 
nothing, so that the roots in this year do not become any thicker. 

The heat wave and therefore the activity of the cambial ring gradually 
disappear in autumn from above downward, just as they had advanced. 
Since the soil remains warm longer than the air, the root has still oppor- 
tunity to continue its growth even if no longer so intensively. This 
explains v. Mohl's observation that roots in December. January and Febru- 
ary are still acti\e in thickening the cell walls of the last formed annual 
ring. 

Definite figyres will give the clearest idea of this. v. Mohl found in 
the winter of 1861-62 that the root formation in a sweet cherry tree had 
not stopped by the 4th of April. In this the branch buds had already 
developed a length of more than 2 cm. and the new wood ring in the parent 
branch had so far matured its new ducts that their pitting was recognizable. 



1 Ebermayer, Die physikali.schen Einwirkungen des Waldes auf Luft und Boden. 
I, Aschaffenburg 1873, p. 119-39. Measurements show that no essentia! difference 
exists between the temperature of the trees (breast high) and of forest soil. With 
increasing depth of soil and height of tree, however, the differences become marked. 
In general it is found that, from October to March, forest trees are colder than 
forest soil. "The roots in this period are the warmest part of the tree; the mean 
tree temperature decreases with increasing height and is lowest in the branches and 
twigs." "In the summer half of the year (April up to and including September), 
conversely, forest trees are warmer than the soil, i. e., the temperature of the tree 
decreases from above downward and, during the day, is highest in the twigs and 
branches, lowest in the roots." The mean annual temperature of the tree fluctuates 
between 3.9 to 6.7 degrees according to the elevation in the plane of growth. It is 
less than the mean air temperature and higher than the mean soil temperature of 
the forest. 

2 Lehrbuch der Baumkrankheiten 1882, p. 177. 

3 Compare Krutsch, Untersuchung tiber die Temperatur der Baume, etc. Jahrb. 
d. Kgl. Sachsischen Akad. zu Tharand, v. X, 1854. 



5^4 

The wood cells lying between the ducts were still thin-walled and had only 
half their typical size. In the roots, hozvci'cr, the outermost wood cells of 
the prez'ious annual ring had not once been thickened. After the tree had 
blossomed; on the nth of April, investigation still showed no complete 
termination of the previous annual ring in the roots and not until the 26tli 
of April did the roots become dormant. 

At the time the new annual ring in the branches of the previous year 
was already completely lignified and so thick that six successive ducts could 
be counted in a radial direction in the lowest part of the trunk, only a 
single row of ducts had developed and only the innermost wood cells were 
found to be thickened. In the main root, the annual ring of the previous 
year was complete and the cambium already prepared for renewed activity 
since the bark could be easily separated from the wood body : nevertheless, 
no traces could be seen of a new wood ring. The bark of the lateral roots, 
which were as thick as one's little finger, could not be loosened. Thus no 
complete winter rest was present here. They lingered in this condition 
until the 30th of April, when some of the leaves were already fully grown 
and a new wood ring in the main root had begun to develop young, still 
unthickened ducts. 

We will get an insight in regard to the second of the above mentioned 
points, i. e., the anatomically different structure of the roots, conditioning 
a lesser power of resistance, if we bear in mind the time when the annual 
rings in the trunk would be developed in contrast to those of the root. 

In the trunk growth, the complete termination of the annual ring will 
take place so much the earlier in the year the higher it is in the tree top. 
Consequently its development there will consist chiefly of spring wood. 
Before the production of the annual ring has extended to the base of the 
trunk, summer has come and there is not much more time for the develop- 
ment of spring wood. Therefore, the dififerentiation of the annual ring 
must so proceed that (no matter whether it is thick or thin) the relative 
amount of spring wood to autumn wood decreases from above doivnward, 
i. e,, relatively, the autumn w^ood increases toward the base of the trunk. 
This hypothesis has been actually confirmed by direct measurements made 
by V. Mohl\ as well as by Hartig- and Sanio". It should be added here 
that the thicker the part of the trunk is the higher the maximum of warmth 
it attains*. 

The firmness of the base of the trunk depends upon the predominant 
formation of autumn wood. 

The character of the tree variety comes into consideration in the devel- 
opment of the root wood. In conifers, with their early termination of root 
growth, the development falls at a time of greater soil warmth and dryness 



1 loc. cit. 

2 loc. cit. 

3 Jahrblicher f. wissensch. Bot. IX, p. 155ff. 

4 Ihne. tJber Baumtemperatur unter dem Einfluss der Insolation. Bot. Cen- 
tralblatt 1883, No. 34, p. 234. Vonhausen, Untersuchungen Uber den Rindenbrand. 
Allg. Forst- und Jagdzeitung-, 1873. 



565 

and, on this account, chiefly autumn wood is formed. If much material is 
present, i. e., the annual ring is broad, a strong autumn wood ring has been 
developed (v. Mohl). In deciduous trees in which the development of the 
root body is continued until the next year and, in fact, as has been shown 
above, often does not end before the blossoming time of the next growth, 
all diiTerentiations are weaker and the boundaries of the annual rings less 
distinct. Since it becomes spring in the layers of the soil only after it has 
become summer above ground, spring wood is always formed in the roots. 
In the further advance of the annual ring, its development depends on the 
degree and continuance of the soil warmth and dryness. If a year has a 
long dry period, autumn wood is formed. If this is not the case, develop- 
ment is limited to spring wood, with only a weak beginning of autumn wood 
formation. Hence the porous structure of the slender ringed root. 

By briefly repeating what has already been stated, we can summarize 
the difiference between root and trunk in deciduous trees, since first the 
annual rings in the root are much more slender than the corresponding ones 
of the trunk and, second, in the constant development of porous spring 
wood, these slender layers are predominantly porous. In conifers the same 
dift'erence is found between trunk and root, so far as the slenderness of the 
annual rings is concerned and, in the same way, the thicker the annual 
ring the more the autumn wood decreases in proportion to spring wood. 
The wood cells are everywhere longer and wider and their walls thinner 
in the roots than in corresponding parts of the trunk. 

Therefore, greater attention should be paid to the freezing of the roots 
Itecause in this is found the explanation of numerous cases of summer 
death in indi\idual trees and groups among those of the same age and of 
the same species. Trees with frozen roots, like healthy ones, usually 
sprout in the spring and often develop normal shoots, even if they bear as 
a rule smaller leaves. Not until summer, but then advancing especially 
quickly, does a yellowing of the leaves begin and also a drying of the twigs. 
The water supply of the trunk is then used up by the transpiration of the 
leaves. 

Even in localities and varieties when no injury of the aerial axis is to 
be feared from winter frosts, fruit trees in pots should be brought into 
protected places, because of the sensitiveness of the roots and, in open land 
cultures, the natural protection from foliage and snow should not only be 
left but, if possible, increased. In planting tree plantations, it will only be 
possible to carry out the otherwise advantageous autumn planting without 
danger if absolutely hardy trees are used or the planting takes place so 
early in the autumn that, preliminary thorough puddling being taken for 
granted, rooting and a close packing in of the roots in the earth may be 
assumed. Duhamel' observed that a formation of fibrous roots can take 
place even in winter. This was later substantiated by Lindley. In less 



1 Des semis et plantations des arbres, p. 155. 



566 

extensive tree plantations, a deeper penetration of the cold can be pre- 
vented by covering the loosened soil. It is a frequent but not universal 
discovery that the roots of recently transplanted trees suffer more from 
winter frosts than do specimens left in their original place of growth. 

Frost Clefts. 

The temperature inside strong tree trunks can follow the temperature 
of the outer air only slowly and thus the inner part of the trunk is colder 
than the surrounding air from morning until noon but is v^armer in the 
evening^ Then a contraction of the tissues, due to the appearance of cold, 
will manifest itself in the outer layers of the trunk while the core still 
retains its original distension. In this way, dififerences in tension arise 
which become the greater, the sharper the change in temperature. Now, 
with a fall in temperature, the wood body contracts more strongly in the 
direction of the circumference, i. e., tangentially, rather than radially, so 
that the peripheral mantel of the still warmer core of the trunk really 
becomes too tight. It must accordingly be stretched tangentially if it shall 
still entirely enclose the core. If, with increasing cold, it can not stretch 
sufficiently, it must split. In this way tears are produced in the bark of 
the tree which advance the deeper into the wood, the greater the cold and 
the difference between the cooled peripheral and the warmer central tissues 
of the trunk. In great, sudden cold, it has been found that some tree 
trunks crack audibly and then show long, deep gaping splits following the 
twisting of the wood fibres. Some varieties of trees show this phenomenon 
especially frequently. The horse chestnut suifers most of all; besides this, 
the oak, poplar and cherry should be especially emphasized. The cleft 
remains gaping only so long as the heavy cold lasts. With the appearance 
of warmer weather the edges of the split approach one another, even closing 
the wound entirely. The wound, however, is almost never well healed and 
breaks open again the following winter. The process of healing is normal, 
since circumvallation rolls are formed from the cambium, the young wood 
and the bark, and strive to unite. In other injuries with free lying wound 
surfaces, these projecting overgrowth edges, however, do not find the space 
necessary for their extension, but are forced to grow directly against one 
another and to push out over the edge of the cleft wound. They therefore, 
from mutual pressure, form rolls projecting outward, depressed in the 
centre like lips, which are called "frost ridges! 

In Fig. 122 we see such a frost ridge on a strong trunk of Acer cam- 
pestre, which shows a number of radial clefts. One of these has split 
through the stem, so that an outwardly visible cleft has been produced 
which, at the beginning, gaped widely but, with the appearance of warmer 
weather, has become very narrow. When in spring the tree would have 
closed the split by growth of the cambial layer, the circumvallation edges 



1 Squires, Roy W., Minnesota Bot. Studies. Bull. 9, 1895. 



567 

found no room to grow into the cleft and therefore were forced outward. 
On this account we find the hp-hke processes made recognizable in the 
cross-section. Such a process of healing lias not yet been observed in any 
other trunk injury, so that its appearance may be considered absolutely 
certain evidence of frost action. 

Caspary^ has experimentally examined this phenomenon more closely. 
He proved by direct measurement that the coefficient of the distention of 
the fresh wood considerably exceeds that of all solid bodies, even that of 




Fig-. 122. Fiost ridge on the trunk of Acer campestre. (After Prank- Schwarz.) 

iron, tangentially as well as radially, and is exceeded only by air. This 
explains the sudden production of deep clefts. 

The extent to which a cleft opens varies in the same tree species and 
with the size of the trunk, but all cases show that if the frost clefts have 
once been produced (even after they have closed in thawing weather) a very 
light degree of cold is sufficient to re-open them. This is explained by the 
fact that the amount of strength necessary for the production of the cleft 
may be sufficient to overcome the cohesion of the cell elements in the whole 



1 Caspary, Neue Untersuehungen iiber Frostspalten, Bot. Zeit. 1S57, No. 20-22. 
In an earlier treatment, Bot. Zeit. ISSH, p. 449, he also cites the earlier literature. 



568 

extent of the trunks radius; with the appearance of renewed cold in the 
same year, no resistance has to be overcome in re-opening the clefts, and 
the following winter only enough to overcome the newly formed wound 
cover. 

The frost clefts produced in winter, usually extend deep into the inner 
part of the trunk. The tree is unable to form a new cicatrization mem- 
brane in the older wood and, conseciuently, each frost cleft represents a 
persistent, outwardly covered over but inwardly unhealed wound This 
becomes the more significant the more some lateral tangential clefts are 
added to the radial, large frost cleft. These tangential clefts usually extend 
into the layers of the spring wood and may be connected with one another by 
radial cross tears. There then occurs an intersected splitting which makes 
the wood absolutely of no practical use and hastens the death of the tree 
by facilitating the spread of wood-destroying fungi. 

We thus obtain such structures as are shown in Fig. 123, which repre- 
sents a cross-section through an oak trunk which, infected by I'olyponis 
snlfureus from a wound in the branch, has become cleft. 

While the splitting of the trunk, due to long clefts, transversing the 
greater part of the tree shaft' has often been described, the production of 
shorter, shallower clefts, which are more easily closed, has not been suffi- 
ciently investigated. R. Hartig- considered them in the white fir where 
they are often very shallow, appear in the upper parts of the shaft and 
usually coalesce very soon without forming frost ridges. Also, they follow 
the direction of the wood fibres, i. e., usually somewhat at an angle. Be- 
sides occurring in the fir, I find this kind of short frost clefts often with, a 
lip-like wall in the red beech, the cherry and the plane tree. Curiously 
enough, these varieties are distinguished by a bark which remains smooth 
for a long time. In this, the preference for certain sides of the tree, in 
the production of frost clefts, is most easily perceived. If the trees are 
not accidentally protected by adjacent ones but stand free it is possible in 
the majority of cases to determine that the west and southwest sides display 
the most abundant injury from frost. Street plantations of plane trees, 
for example, show how difl^erently the dift'erent sides of the trees behave. 
At the time when the well-known, normal dropping of the bark scales from 
the trunk begins, it will be found that most of them are thrown oft" first on 
the southwest side of the trunk. 

At times "tears due to drought" are described as frost tears. Nord- 
linger" has called especial attention to this. Tears due to drought, whicii 
occur especially in strong trees growing on an impervious soil layer, or 
undergoing a sudden great scarcity of water, are characterized by repeated 



1 Goppert, tJV)er die Folgen ausserer Verletzungen der Baume, p. 30, Breslau, 
1873. He found frost tears in 76 different varieties of trees. 

2 Hartig-,, R., L,ehrbuch der Pflanzenl\ranl<heiten, 3d edition, p. 214, Boi-lin, 1900. 
Julius Springer. 

3 Nordlinger, Trockenrisse (falsche Frostrisse) an der Fichte. Audi ein Grund 
der Rotfaule. Centralbl. f. d. gesamte Forstwesen. Wein 1878, Part 6. 



569 

changes in their radial course in the older annual rings, than in the younger 
ones, or by the radial splitting of one or two annual rings in the wood disc. 
Such inner clefts then have the form of a lance tip, i. e., are broadened at 
the centre. Since in clefts extending to the bark the wound remains open, 
the circumvallation walls incline toward the cleft and, therefore, form no 
projecting ridges in frost clefts. . 




Fis. 123. Oak stem cleft Ijy Polyponis sulfureus. (After Frank-Schwarz.) 



Frost Busters. 

In connection with frost clefts, the so-called "inferno! frost tears" 
should be considered, which R. Ilartig^ has observed in oaks and firs. 

"If the tree shrinks with great cold"-' he says, "tears can arise in the 
wood body on the surface of the cleft which, however, extend only to the 
bark mantel zvithout splitting it. The bark, which has no radial cleft sur- 
faces, holds the wood body together. However, the elastic bark of the nr 



1 Hartig-, R., Innere Frostspalten. For.sll-naturwis.s. Zeit.schr. 1896, p. 483. 

2 Lehrbuch der Pflanzenkrankhelten, 1900, p. 214. 



570 

is distended where the frost tear opens internally and thus loses a part of 
its elasticity. If the tree later grows thicker, the bark exercises a lesser 
pressure on the cambium at this place and the additional growth is, there- 
fore, locally increased. Outwardly the trunk is not round but has ridge- 
like processes." 

I assume a very similar course in the production of the structures, 
which I term frost blisters. These are broadly conical, but usually flattened 
processes at times one centimeter high on the smooth bark of trunks or 
branches two or more years old. 

These blisters should not be confused with the conical bosses, occur- 
ring not infrecjuently on luxuriantly cultivated varieties. In them a hard 
wood core is recognized immediately under the bark, while the frost wood 
blister, in some cases, consists permanently of a soft tissue mass, easily 
indented with the finger nail which, in other cases, lasts only during the 
year of its production. 

The projections, strongly lignified from the start, and for which I 
would like to propose the name of "duct boss," almost always have a 
definite position in relation to the bud, while the frost blisters are found on 
any part of the young trunk or the branch internode. "Duct bosses" are 
bark covered, wood swelUngs with one or two points, which, like the begin- 
nings of a gnarl, project above the periphery of the rest of the wood body. 
They owe their production to the excessive development of the two vascu- 
lar bundles which normally pass into the bud cushions and unite with the 
central, strongest bundle of the vascular bundle body of the petiole. 

In the tender frost blisters we find no connection with the cords of the 
leaf spur. They are found at any place and arise from a blister-like dis- 
tention of the bark body away from the wood cylinder. The young wood, 
lying on the wood cylinder, at once begins cell increase, since the distention 
takes place only in late frosts and, therefore, at the time of growth activity. 
This young wood fills the cavity with a thin-walled parenchyma wood 
which gradually passes over, at the periphery, into normal wood. 

The whole process taking place here is the same as occurs in the new- 
formation of bark on an artificially produced wound surface. In blister 
formation the difference lies alone in the fact that the bark does not scale 
off, but is only raised in places by the frost and that thereby the new struc- 
tures, lying above the wood body, at first do not become visible to the 
naked eye. At times they can be very clearly recognized by their unusual 
luxuriance when the bark is cut on large frost bhsters. It is then possible 
to expose here and there a wrinkled outgrowth, several centimeters long 
and 0.5 to i.o cm. high, which is not connected at all with the old bark and 
only rests on the wood body. In one case (in the pear Bonne Louise 
d' Avranche) the outgrowth had ruptured the bark mantel and had ex- 
tended far beyond the circumference of the trunk as an irregularly outlined, 
somewhat conical mass with a warty, crumbly surface. 



571 

I could observe other stages of healed frost blisters in the maple and 
the apple. As yet the best examples have been found m the maple, and, in 
fact, on two year old shoots, more than 1.5 m. long. Many of these, in 
their whole course, excepting the tip region, and on all sides, showed small 
flat, completely bark covered bosses, possibly 0.5 mm. high which were 
more noticeable to the touch than to the eye. The outer bark appeared 
perfectly normal and the direct continuation of the remaining, not rough- 
ened part of the branch. In cross-section, the cause of the out-pushing of 
the bark may be recognized in the swelling of the wood body which, at the 
Ijeginning of the second annual ring, has formed an aggregation of paren- 
chyma wood cells very broad and rich in starch. As a rule, such an 
aggregation of wood parenchyma is found lying exactly between two 
medullary rays so that the lateral transition from this diseased wood tissue 
to the healthy tissue is rather sudden, while the abnormal wood elements 
assume very gradually in a radial direction the normal dimensions and 
thickness. Only in the radially and laterally adjacent wood with a regular 
structure are found greatly widened and shortened wood cells filled with 
starch (investigated in May). 

In the v^'ood parenchyma aggregations, irregularly extended, yellow 
stripes are found ; the yellow color arises from swollen cell walls which are 
universally present in frost injuries. Also, other characteristics of a 
definite group of frost injuries are present as, for example, the lateral dis- 
placement of the medullary ray cells at the frosted place and the barrel- 
shaped widening of the medullary ray where it enters the parenchyma 
aggregation. This barrel-shaped widening of the medullary ray is pro- 
duced less often by the increase of its cells than by their broadening at the 
expense of their length. In this, not infrequently, a very striking thicken- 
ing of the secondary membrane is noticed. Cell increase is found most 
frequently in the one-celled medullary rays which, from the point injured 
by frost, become two-celled. The further such a medullary ray extends 
into a parenchyma aggregation, the broader and shorter its individual cells 
appear in cross-section and with relatively more slanting w^alls ; they dove- 
tail into one another, instead of remaining bluntly placed against one 
another. At last the shape of all the cells in the parenchyma aggregation, 
of which the elements are widest near its centre, become the same so that 
no difference can be recognized in the medullary rays. 

A brown bark zone, tangentially elongated, which was formerly con- 
nected with the parenchyma but is now separated by newly interposed 
wood, corresponds in the same ''adius to the yellow or brown striped 
aggregations of parenchyma wood. 

By coloring the section with campeche wood extract, very interesting 
pictures are often shown, if a concentrated solution of chloriodid of zinc 
is added. The difference in thickness in the walls of the wood cells 
becomes more apparent. The walls of some groups of wood cells are 
colored more intensely yellow and are more swollen. 



572 



These were the walls of the radially divided zvood cells^ surrounding 
the ducts and containing starch zvhich, therefore, might he more sensitive 
than the other elements of the vascular bundles. 

In frost blisters of the cherry, illustrated in Figs. 125 and 126, the 
anatomical structure evidently differs from that of the frost blisters of the 
maple branch, inasmuch as here the gvimmy exudation usually sets in as a 
result of the injury. Fig. 125 is a cross-section through the centre of a 
blister. Fig. 126 a longitudinal section made at one side of the medial line 
of the wound ; r is the brown stripe of dead tissue which immediately 
bounds the inner, fine tear which caused the blister. This tear was not 
visible externally since the outermost bark layers {e) had remained unin- 
jured, although the wound was deep and extended to the old wood (A). 
It must from the beginning have been very narrow, however, and produced 
at a time when an immediate overgrowth was possible since the overgrowth 
tissue had sunk at once into the wound (r) without causing the death of 









P 



1 If, at the time of the awakening of vegetation, cross sections of Acer, Salix 
viminalis, and other ti'ees are treated with a strongly acid, concentrated solution 
of chloriodid of zinc, large dark blue, variously shaped starch structures may be 
seen to pass out frorn these radially divided wood cells (compare Fig. 124 r). The 
forms of these are different. At times they may clearly be seen composed of sep- 
arate, iiTegular, swollen starch grains because the cores, remaining firmer, appear 
granular on the smooth upper wall surface of the pouch-like structure; they are 
left after the dissolution of the peripherial layer of the starch grains. At times, 
however, the substance of the hollow body is uniformly membraneous and the upper 

surface smooth; the 
tip often appears 
notched. In older wood 
such starch structures 
appear most numer- 
ously in the autumnal 
wood of the last two 
annual rings. Glycerin 
clears up the starch 
pouches which occur 
on the upper side as 
well as the under side 
of the section. Alcohol 
brings out their con- 
tours more sharply 
and makes them seem 
d a !■ k e r. Potash 
bleaches them and 
shows better the gran- 
ular elements of the 
walls! Their formation 
seems to retult from 
the swelling of the 
starch grains which 
they rupture and, with 
the reagent, transform 
their contents into a 
membrane in which, 
at times, bright cir'cu- 
lar spots may be seen, 
just as if vacuoles had 
been deposited during tlie formation. The notched form of the tip is conditioned 
by the irregular pushing forward of the individual, outermost starch giains. I 
would like to consider these structures Traube's cells; strongly acid chlorzinc with 
potassium alone showed a membraneous precipitate. Tin-chlorid (neutral) and 
iron chlorid (acid) produce no such structures. They are also not destroyed by 
sulfuric acid or hydrochloric acid. A drying of the branches which had previously 
displayed many such structures, decreases their formation or stops it entirely. 
This phenomenon can not alway.s be produced. It seems to be connected with the 
special constitution of the starch shortly before its dissolution in the early .spiing. 




Fig. 124. Starch structures formed in the treatment of 

sections of a young willow branch with chloriodid of zinc. 

They pass out of the bisected wood cells and often curve 

into the duct lumina. 



573 

considerable amounts of tissue. This young tender overgrowth tissue, as 
well as the cells bounding the diseased parts of the bark, at once produced 
thick bark layers (kn) which completely encased the dead tissue and iso- 
lated it from the healthy tissue. The hard bast bundles (b) which, in the 
midst of the healthy bark tissue, became diseased immediately about the 
wound, had been enclosed by isolated cork circumvallation (Fig. 125 u) so 
that from them no further decomposition of the surrounding bark paren- 
chyma, containing chlorophyll, could take place. 

In the process of healing, the new wood (n h) and the new bark (n r) 
endea^■or to cover the wound, beginning at the sides and extending inward. 




nh___ 'l_ 






■■f>p 









•I V'' 



Fig-. 125. Frost boil on a branch of sweet cherry. Medial section. 



In the centre of the wound, where the gaping edges stand further apart 
(Fig. 125 n h) no closing has yet been possible. On the other hand, this 
is the case at the sides. The edges of the two new wood layers (Fig. 126 
n h and n h' ) have become united and the dead piece of the bark (Fig. 12611) 
is separated from the dead piece of the wood. The older and thicker the 
new wood and bark layers become, the more the dead bark is pushed out- 
ward and finally pushed off. The dead wood {h p), of a parenchymatous 
nature, and the momentarily fresh wound edges (Fig.. 125 ]i p'), likewise 
formed of parenchyma wood, at first gradually pass over into firmer, normal 
tissue. The first formed new wood, suitable for circumvallation, bears in 
itself, in the central wound region, the germ of death; numerous gum 



574 



centres (Fig. 125 g) have been formed, which in a short time will dissolve 
the less resistant tissue. 

In older circumvallation on a maple branch, which was not at all lux- 
uriant, a splitting of the annual ring was noticed, since the region of the 
autumn wood on one side of the branch was divided into two parts by a 
considerably thicker zone of spring wood, rich in ducts, and then reunited 
with the zones first formed so that one more annual ring could be counted 
on one side of the twig than on the other. 

When such excrescences are remarked for the first time in trunks 
which, up to that time, had been healthy (this is the case in the early summer 
months) it will be advisable to strongly scarify the tree. The knife could 
be inserted above the excrescence and several long cuts be made through 
the blister into the healthy underlying tissue. By the wound stimulus thus 




nr 



nh 




nA 



^U:r,l^,^,x^ 



/5/ 



l/L 



hfv 



Fig\ 126. The same wound as in Fig-. 125. A lateral section. 

ii;;:s'ij;i]i!i:n!iMiwto.'!j;::,/rii:.i tii:y^'*ii.jiii \\\\u\\\\^ i, , > 

brought to bear on the healthy tissue near the blister, it is incited to an 
increased circumvallation activity, and the pressure of the diseased excres- 
cent tissue on the plastic underlying material is reduced. 

Frost Wrinkles. 

While the raising of the whole bark body from the wood cylinder 
found in places in frost blisters could be proved to have been their cause, 
in frost wrinkles a loosening of the outer, coarser bark layers from the 
tender, inner bark is concerned. The phenomenon has been observed as 
yet only on the new growth of cherry branches in June. The branches 
were conspicuous because of the coarse w^rinkles on one side of the other- 
wise smooth bark. The cambium was not disturbed, the pith was some- 
what browned. 

As has been proved, a penetrating frost produces great dififerences in 
tension in the trunk. The frost, without necessarily forming frost crystals 



575 

in the intercellular spaces, contracts the tissue, and so much the more the 
thinner walled the tissue is. The bark suffers considerably more than does the 
wood which, reached later, cools down less easily and contracts less. The 
tangential contraction is greater than the radial. This dift'erence acts likes 
a one-sided strain, taking place in the direction of the circumference of the 
trunk to which the different layers of the bark will respond to a diff'erent 
degree, when the bark, as a whole, is very young. With an equal amount 
of contraction at all points in the bark, the cells lying nearest the periphery 
and most elongated in the direction of the circumference of the trunk, will 
be most displaced. If one considers that the outer cells of the primary 
bark, because of the great coarseness of their walls, are not as elastic as 
the underlying, thinner-walled ones, it is clear that, when the strain ceases 
in them the permanent increase, caused by the incomplete elasticity, will be 
the greatest. 

After the frost action has stopped (it continues only a short time in 
late frosts) the increased turgor will cause the cells to retain their distended 
form and, since the outer, greatly distended bark layers no longer have 
sufficient space in the previous tangential plane, they become raised in 
wrinkles or blisters above the plane of the circumference of the trunk and 
in this way form "frost wrinkles." 

Besides the tangential and radial contraction, there is an additional, 
longitudinal change in the young, still herbaceous twigs, which must be 
produced with the twisting of the axillary body, caused by the frost action. 
One can easily produce cross wrinkles artificially on one year old shoots 
by bending them. Reference should be made to a work by Ursprung^ in 
regard to the tensile conditions developing in bent, herbaceous stems. 

Bark Tatters and Cork Holes. 

The loosening processes which set in after a drying of the outermost 
tissue layers when the branches have been killed by frost occur more fre- 
t|uently than the phenomena of raised bark, appearing in the form of frost 
wrinkles and blisters in living bark tissue. In Fig. 127 is shown a branch 
with loosely rolled back, flapping, dry bark tatters on the autumn (Sylves- 
ter) pear. Even in the soft wooded apples (Morning Breath) the 
phenomenon was found in May and June, on branches and young, still 
smooth barked, sapling trunks. The periderm is seen at first to be dis- 
tended in blisters ; later the blisters split longitudinally. The whole bark- 
parenchyma underneath the tear seems blackened and dries up quickly. 
The death of the bark tissue advances further, the more the tear widens, 
since it at first becomes yellowish green and tender, then grows dark, col- 
lapses and finally dies. 

In time these dead spots become entirely bare, since the longitudinal 
tear in the periderm blister lengthens and new cross tears divide the whole 



1 Ursprung-, A., Beitrag zur Erklarung' des exzentrischen Dickenwachstums an 
Kiautpflanzen. Ber. d. D. Bot. G. 1906, Part 9, p. 498. 



576 

raised cork into many tatters. In drying, the various tatters curl backward 
and thereby expose the bark parenchyma which has been covered. It 
should also be observed that such cork tatters are most frequently found 
directly at the base of the young, still smooth barked trunks, while the 
younger shoots seem oulwardly unaffected and also sprout but, yet, after 

some time, the leaves turn yellow and wilt. 
The life of the tree depends on the 
extent and frequency of such holes in the 
cork which are found repeatedly separated 
from one another by healthy spots. The 
tree usually dies since the cambium under 
the blackened parts of the bark is dead. 
The region near the buds or near cut 
branches seems especially disposed to such 
injuries from frost. 

TiiF. Phenomena of Discoloration in 
Trunks and Branches. 

I'Vuit growers in spring pruning usu- 
allv decide after a consideration of the cut 
surface, whether a variety of fruit has 
[jroved hardy for a certain region, or has 
been injured by the cold. The decision is 
made according to whether the cut surface 
is uniformly white or browned in places. 
The browning sometimes occurs in circular 
zones, sometimes in flat surfaces. In the 
first case (often on one side of the branch) 
the cambial region, or the periphery of the 
pith disc, the so-called piih crozun where 
tlie innermost ducts of the wood ring pene- 
trate into the pith parenchyma, is the centre 
of the discoloration. In the surface brown- 
ing, a part of the wood surface together 
with the pith body is usually attacked on 
that side of the branch where the bud lies 
Fig-. 127. Raggedly torn cork which belongs to it. The discoloration is a 
luinellac on branches injured by ■ q£ ^j^^ humification which setS in 

frost. ^^ 

gradually in the walls when the cell con- 
tents dry up. Not infrequently phenomena of swelling are noticed in the 
brown cell walls. 

If different parts of the trunk are frozen, brown stripes are found at 
times extending downward to different depths in the wood body; in the 
browned parts through its whole diameter. These stripes often have a 
symmetrical arrangement so that a cross-section through the semi-healthy 




577 

part of the trunk shows a regular, brown hgure. Most well-known is the 
"Landzuchr cross" in the maple and similar structures in Cytisus and 
Fraxinus. Cytisus and other Papilionaceae show at times a very attrac- 
tive bright coloration of the cross-sections which should be made of 
practical use. The bright coloration is caused by the different degrees of 
browning in the heart wood and cambial zones. 

Such regular, surface-like discolorations are of rare occurrence. The 
most frequent phenomenon consists of an irregular browning of those parts 
of the bark which surround a bud and of those outcurvings of the pith 
which lead to this bud. The amount of tissue disease naturally depends 
upon the time and intensity of the action of the cold as well as the specific 
sensitiveness of the variety and, with equal intensity, on the age of the axis. 
As a rule, the younger a branch is, the more extensive is the tissue browning. 

The cross-section, shown in Fig. T28. of a pear branch injured by 
artificial frost, gives an insight into the variety of browning due to frost. 
In this, m indicates the pith body, ;;/ k, the pith crown. /;; h, the outcurving 
of the pith disc, called pith hrldijes, which lead to the bud, lying close above 
this section but not visible in it. At the place where the bud lies, each 
stem is more or less thickened and pushes out from a "hud cushion." In 
this bud cushion lie also the vascular bundles //' and //". which pass down- 
ward into the petiole, in the axil of which is found the bud. The cap of 
tissue, which, in the drawing lies above the central cord of the leaf spur, 
and seems laid against the bark body of the twig, represents the cicatriza- 
tion tissue w'hich had formed in the previous year after the falling of the 
leaf. The different ducts in the cords of the leaf spurs and in the wood 
ring are distinguished by //,' //" and //. The wood ring (/?) with the medul- 
lary rays (;;; s) shows diverse, predominantly radial clefts, while the tissue 
openings (/) in the bark tissue usually extend tangentially. Noteworthy is 
also a gaping, longitudinal split which breaks the pith bridge and, by the 
amount of injury, makes apparent that it represents the part of the branch 
most susceptible to frost. 

In many deciduous trees there is still a second region of great sus- 
ceptibility to frost, viz., the hard bast cells and their outer parenchymatous 
covering. In my experiments with artificial freezing, cherries, plums, red 
beeches and apples w^ere proved especially susceptible, while pears showed 
a greater power of resistance. In the adjoining picture the bast bundles 
{b) are found to be unattacked. Just as little is the coUenchyma (c/j. 
The cambium zone ic) which, by its brow^n color, indicates to tree breeders 
in the spring pruning of fruit trees that the branches have been injured by 
frost, has not been browned in the pear. In microscopic investigations, it 
is found that usually the still cambial, thin-walled, young wood and the 
innermost young bark, of the same age, have been browned, while the 
meristem layer, rich in cytoplasm and lying between both regions, a[)pears 
colorless and uninjured. 



5/8 

By surveying- the cross-section as a whole, which may serve as an ex- 
ample of frost discoloration for all trees, we see that the region of the bud 
cushion is the most susceptible part of the branch. In this region the twig 




Fig. 128. Browning- and splitting- of the tissue of a pear brancli produced by 

artificial frost. 

has the slenderest wood ring and the largest accunudation of parenchyma. 
The spots kept dark in the drawing represent the browned parts. So far 
as susceptibility is concerned, the pith crown and the medullary rays follow 



579 

next. The pith hody itself usually does not suffer until later and the older 
the branch is the less is the injury to the pith body. In the present case,, 
the experiment was carried out toward the middle of May, at which time 
the storing of starch had already taken place in the pith and bark. The 
injury to the pith was limited here to a checkered marking of the pith disc, 
while the contents of some of the cells containing starch had turned brown. 
Investigation showed that the cytoplasmatic substances, and not the starch 
grains themselves, were discolored. 

The irregular distribution of cells browned by frost in all tissues can 
be explained only by the different cell content. Probably cells rich in 
sugar are the most susceptible. The cytoplasmatic content has suffered 
even when the cell membrane is still clear. In injuries to the pith crown 
the narrow, spiral ducts are the first ones to be browned. 

The Frost Line. 

Mention was made in the previous section that the fruit grower usually 
considers the browned cambial region as an indication of frost injury. 
This zone is now often termed "frost line." Even unskilled forest workers 
showed me, as frost lines, the circular zones, setting in after spring frosts, 
between older annual rings with which we will later become better ac- 
quainted in the discussion of "false annual rings" and "moon rings." By 
these terms are understood the brown circular, or zigzag stripes found by 
testing microscopically the tissues injured by frost. These stripes are com- 
posed of collapsed misshapen parenchymatous cells, and occur very olten 
but as yet have been but little studied. I have investigated more exactly 
the phenomenon on branches of an apple tree which had been forced in a 
greenhouse and then, in May, exposed for only 22 minutes to a temperature 
of 4 degrees C. below zero. 

By the middle of June, in the experiments carried out on a branch of 
which the tip was frozen, a sharp boundary was found between the dead 
part and that which had remained alive. This observation is confirmed 
in all frost injuries. A (jradual extension of the injured zone does not 
become noticeable subsequently, if no secondary factors, such as wood- 
destroying fungi, enter into co-operation. However, the action of the frost 
itself can radiate out into the healthy tissue in the death of certain parts as 
was the case in the experiment under consideration. If the branch which 
had died after its tip was frozen was cut off directly below the bud which, 
adjoining the dead tissue, had remained healthy and had sprouted, a 
browned, sharply defined stripe was found to extend from the dead places 
out into the healthy part of the axis past three healthy buds. This stripe 
traversed the axis in a diagonal direction from the outside inward. 

The sharp limitation of the brown stripe and its diagonal course were 
explained by a microscopic investigation. This proved that the main 
vascular bundle of the lowest dead bud of the frozen tip is involved here. 
This was, therefore, a case where the death of the bud (jradually induced 



58o 



the dying hack of the conductimj cord (vascular bundle) ivhich traversed 
the healthy tissue and the tissue ivhich became diseased. This, therefore, 
could be the only after-effect which can take place in frost injuries in case 
there is no subsequent parasitic infection. 

In order to discover which 
might be the very first effect of 
frost on the tissue of the tree 
and, therefore, which injury sets 
in with the appearance of ver\' 
light frosts, a whole course of 
experiments was made on the 
effect of slight degrees of cold, 
but they did not lead to the de- 
sired results. Either no effect at 
all was shown or the above-men- 
tioned initial stages appeared 
simultaneously. The pruning was 
extended further and further 
back from the completely frozen 
tissues into the healthy, basal part 
of the twig and observations were 
made to see which disturbance 
had extended farthest from the 
frost centre into the healthy tissue. 
The frost action which could 
be traced farthest into the 
healthy ivood was found to be 
the swcUinij of the intercellular 
substances, i. e., the middle la- 
mella (Fig. 129 i). 

I found this striped swelling 
and browning of the intercellular 
substances to be in general more 
frequent tangentially than in the 
direction of the medullar rays, 
especially often near the old 
autumn wood, i. e., in thei first vas- 
cular layers of the spring wood. 
But this condition of the inter- 
cellular substances is rarely found by itself ; it is usually associated with a 
slight yellowish colormg and swelling of the secondary membranes of the 
adjacent wood cells (Fig. 129 A). In some cases this change becomes so 
extensive that the entire cell lumen is filled, excepting a narrow cavity (hh). 
The power of refraction becomes extraordinarily weak with the swell- 
ing, being retained only by the outermost membrane and the firmer, inner 




Fit;-. 129. 



Swelling- of the cell walls' after 
artificial frost. 



58i 

lining. The swelling" can become so great that even the outermost mem- 
brane tears {p) and this tearing, as a rule, extends to several adjacent cells, 
so that the changed secondary membrane with the swollen intercellular 
substances, coalesces into a uniform yellowish to brown stripe in which 
are recognizable parallelly deposited remnants of the primary membrane 
(si). 

It has thereby been proved experimentally that processes of looscnlnq 
are initiated in the cell membranes by frost. These become apparent in 
the so-called "frost lines." 

Internal Splitting of the Trunk and Branches. 

In the section on frost blisters, the disturbances were considered which 
take place in smooth l)arked branches and trunks without any external 
injury being noticeable at first. Not until the year following the produc- 
tion of the blister do the primary bark layers, which cover the frost blister, 
rupture because this l>lister has gradually enlarged. These torn bark 
layers surround the protruding new structure as dried edges. The cause, 
however, is to be seen onlv in the raising up of the hark layers, without 
anv splitting of the w^ood. 

If, howe\'er, the occurrence out of doors in so-called frost holes, i. e., 
places where late frost occurs almost annually and very extensively, is 
more closely examined, blister-like protuberances will be found on the 
branches and trunks which internally show repeated splittings of the annual 
ring. 

I have accidentally succeeded in producing such blisters artificially by 
exposing to sharp brief frost action branches in which the wood ring of the 
current year had attained a considerable thickness. The subjoined Fig. 130 
represents a healed inner wound, due to the splitting of a cherry branch. 
The frost wound has been produced by a one-sided raising of the bark from 
the young wood, a is the old wood of the previous year; b, the spring 
wood of the current year, formed before June ; g is the sapwood region 
with the normal cambial zone. About this time the branch was placed in 
a freezing cylinder. It was found, in the subsequent investigation, that the 
bark had been split oft" from the sapwood in a wide curve (s p) and that 
the young w^ood {h) seemed split radially. The splitting extended along 
the medullary rays which more rarely were torn apart than loosened at one 
side from the prosenchymatous cells and ducts and then partially dried up. 
A radial enlargement of the holes represented at in the drawing takes 
place in many cases because of the extensive drying of the prosenchy- 
matous cambial elements which are still partly thin-walled. In general the 
radial clefts in the wood remain slender and only the walls of the elements 
which drew apart from one another turn a deep brown. 

Near the breaking buds in which a medullary bridge traverses the 
whole wood body from the pith to the bark in all trees, the tissue is more 
tender, the number of thick-walled cells is less ; the elements lying next to 



S^2 

the medullary rays have developed into wood cells with strongly refractive 
walls, while the cell forms, to be found at a further distance from two 
medullary rays, are still thinner-walled and richer in content, also showing 
no broad ducts between them. In such sapwood layers, near the bud, a 
tangential clefting of the tissue on the line between the wood of the pre- 
vious year and that of the current year is found at times as the continu- 
ation of the radial split. 

Radial holes (/) in the tissue of the secondary bark (n), correspond 
to the clefting of the wood body, while the primary bark (jn) with its hard 
Ijast bundles (h) shows no ruptures whatever but only a partial browning 




Fig. 130. Internal splitting of a clierry liranoh produced by artificial frost. 



of the contents and of the walls of some of the hard bast cells and l:)ark 
parenchyma cells (r). Here also the holes are produced often by the 
separation from one another of the different tissue complexes, less often 
by the splitting of the membranes of the individual cells. The thin- 
walled cell groups which, in the secondary bark, correspond to the bast 
parenchyma of the primary bark, separate from the bark rays which have 
already advanced further developmentally and are, therefore, thicker 
walled. At the sides of these bark rays the rows of cells, accompanying 
the hard bast cords and containing calcium oxalate, are especially noticeable. 
The radial splits and clefts, however, are only secondary phenomena 
in comparison with the great tangential clefts (s p) which separate the bark 



583 

from the wood. The Hne of separation extends irregularly, sometimes in 
the cambial layers of the bark, sometimes into those of the sap-wood. Since 
it can be assumed that in all parts of the tissue of the line of separation an 
equally strong strain was active in producing the tear, it is evident, from 
the irregularity of the line of separation, that the tissue at the same radial 
distance from the centre of the branch does not possess throughout the 
same firmness. Such an irregularity is shown by the tissue fragments (k) 
which, remaining attached to the sapwood, die later and are indicated at 
the side of the projecting wood (/), 

\\'ith the exception of these fragments very little collapsed tissue is 
found at the torn place, even the cells of the youngest bark (w), which 
have turned a deep brown and become poor in contents, have not collapsed. 
Instead they have become stiff and their walls (i) much more resistant to 
sulfuric acid. 

The healing of such wounds does not as a rule take place by lateral 
circumvallation. Rather, in similar places, a radial stretching of the older 
cambial parenchyma is observed at first. Later isolated meristemic aggre- 
gations are produced in the bark between the bark rays which form new- 
wood elements. The new wood gradually presses the tissue layers (;/) 
which, in this case, have not been changed, against the split sapwood in the 
direction /, o. c, and forms from the dead tissue remnants a brown stripe 
which becomes narrower with a greater v^'ood accumulation above the place 
of rupture, i. e., greater pressure. The isolated meristemic zone of the 
luood bundles, produced in the raised pieces of the hark, later unite 
laterally with one another and. finally, with the cambial zone (/), pro- 
duced on all sides of the still uninjured branch. Such a blister, produced 
by tangential raising and radial splitting of the wood ring, may remain 
recognizable externally for many years. 

Open Frost Tears. 

An apparently \ery unessential phenomenon, to be found most easily 
in vigorously growing nursery specimens, is the occurrence of small tears 
which have been overgrown. These extend also, more or less like blisters, 
above the smooth bark but are distinguished from those already described 
in that they have a long grove on their upper surface. From this it is 
evident that they have been produced by the coalescence of the two edges 
of wounds which have pushed forward like lips. These elevations grow 
less and less conspicuous with later growth and finally have no further sig- 
nificance for the life of the trunk. 

These are, however, of uncommon theoretic importance in explaining 
the production of the tissue excrescences described later as frost canker. 
So far as my investigations have gone, they support the theory that the 
Swellings of frost canker have their origin in such small tears as are pro- 
duced in the spring at the time of the most luxuriant cambial activity of 
the trunk. Such tears are found usually in the immediate proximity of the 



5B4 

buds and their appearance can be traced back i)rimarily to a local increase 
in growth. It cannot be denied that this is the most pertinent explanation, 
but the condition of the wound in many cases also indicates some frost 
action. 

It is finally possible, in artificial frost experiments, to produce such 
frost tears and thereby put an end to such doubts. Fig. 131 gives the 




Fi.£ 



131. Cross-section through the luid cushion of a hirch branch, injured by 

artificial frost. 



anatomical appearance of such a Avound which had been produced by the 
action of artificial cold on a larch branch a year and a half old. The 
branch was cut through a bud cushion; the wood (A), which otherwise 
would have form.ed an uniform ring about the pith (m), appears inter- 
rupted by the broad parenchymatous medullary bridges {m-mtr). 



585 

This tissue has been killed by frost and torn by the subsequent drying. 
The parenchyma, lying in the direction z'-Z'a, had not been formed at the 
time of the frost action (May i8th), but the splitting of the medullary 
bridge was extended outward through the bark. The bark in the cambial 
zone at that time was also split away from the sapwood at both sides and 
formed the split (s p) but only the cells lying directly on the edges of the 
wound had died and partially dried. The two sides of the bark above the 
split {s p), which originally had been separated, at once formed the initial 
stages of the overgrowth edges in the manner common to all processes of 
circumvallation by the outcurving of the peripheral healthy cells and their 
division. These overgrowth edges are formed further and further out 
toward one another until in a short time they coalesce. 

The place of coalescence of the circumvallation edges {n r) may be 
recognized by the diseased depression (z- a), but especially by the position 
of the hard bast cells (h), which seem inclined toward one another. The 
whole tissue, which covers the split, has been formed anew in the course 
of six weeks (the wound was investigated on the 4th of July). The old 
bark, which had been split by the frost tear, is pressed back by the lip-Uke, 
protruding circumvallation edges and now surrounds the new structure 
like a sharp edge {t). The circumvallation edge at this time had formed 
wood. The whole thick-walled zone (hp) is new wood. This, however, 
has been produced with so little bark pressure that it has become parenchy- 
matous and short celled. Only later did the cambial zone (c-c), produced 
by the coalescence of the zones, which had been isolated in two halves, form 
normal wood elements and deposit firmer layers about the frost wound. 

Similar to this injury to the larch is a wound produced on an apple 
branch by the action of cold at 3 degrees C. which lasted for 25 minutes 
in July (Fig. 132). In this, a indicates the old wood of the previous year; 
b, new wood formed up to July; c, the region in which the cold had killed 
the tissue. In the very luxuriant overgrowth edges, extending above the 
surface of the wound, the spirally curved cambial zone (/) has produced 
a thick new bark (.7) and a new wood body (e) , divided radially by the 
medullary rays (d). But this formation of wood from prosenchymatous 
elements begins first rather far back in the circumvallation edge. The lip- 
like part of the edge, lying in front of it, consists of parenchyma wood, on 
the edge of which may be recognized gradually ditfering prosenchymatous 
cell groups (h). In the same radius, in which the first thick-walled wood 
cells occur, the beginnings of the hard bast cells (h b) appear in the bark. 

The circumvallation edges extend over the bark as a knob with a lip- 
like cleft. This appearance is retained because of the natural swellings 
which are met with at times in the branches from cankered trunks of 
apple, beech, ash and cherry trees, and which I consider to be the initial 
stages of the closed canker swelling (cf. Fig. 135 in the tfollowing 
section). 



586 

Canker (Carcinoma). 

As "canker," I consider those wounds which de\elop their overgrowth 
edges into excessive wood swelUngs. The character of the excrescence hes 
in the exclusive, or predominant formation of parenchyma wood instead 
of the normal prosenchymatous wood elements. The canker excrescences 
have a typical form for each tree variety. 




Fig-. 132. Overgrowing frost .split in apple branch, produced by artificial cold. 

a. Canker of the Apple Tree. 

The canker of the apple tree occurs in two forms, of which the more 
common one is distinguished by a broad, central exposed wood surface 
formed from the open, protruding, blackened wood body and is surrounded 
by roll-like, strong calluses, developing outwardly each year like terraces. 
At the centre of the wound is found frequently the remainder of a small 
stump of a branch. This is indicated in Fig.. 133 by c, while the nearest 
overgrowth edge is indicated by u'. We see how the wound surface gradu- 
ally increases since the first formed, still rather flat edge dies and turns 



5^7 



lilack, while that n\ tlic next year (u") develops in the form of terraces. 
The process is repeated from year to year (see u"'-\i"" ] until nearly the 
whole extent of the axis has been attacked by the canker excrescence and 
dies. Such places, with open wounded surfaces which become wider and 
wider, are called "open canker." 

The increase in thickness of the overgrowth edges toward the outside 
is explained by the fact that plastic material, coming from above, from still 
living, leaved twigs, has to be divided in each successive year over a smaller 
part of the twig or trunk surface because of the retrogression of the over- 
growth edges and accordingly provides relatively more abundant food 






i 


.i 


/ 


w m-n 


1 


ls«r:«* 


^^ 


U ' '^aoj^^jgam j^H^^WI 


|r 


^^^^^BBO^Titf^-'ir 




1 


I 



Fig. 133. Open apple canker. 



Fig. 134. Closed apple canker. 



substances for the formation of new parts, in the cambial zone, which is 
growing shorter and shorter. 

The closed canker (Fig. 134) when completely developed, represents 
approximately a spherical wood excrescence (m) at times exceeding the 
diameter 3 or 4 times, knotted and usually completely covered with bark. 
This wood excrescence is flattened at its tip and deepened in the centre of 
the upper surface like a funnel {f). In contrast to open canker, this swell- 
ing covers a much smaller part of the axis bearing it but makes up for its 
lesser extent in width by a considerably greater radial elevation, i. e., greater 
height. 



588 

Blight may often be proved also on the branches and twigs on which 
occur canker excrescences. In all three varieties of injury a bright red to 
brown, flat conical, or oval fruit body of Nectria diiissima may be found, 
not infrecjuently, in winter on the dead, cracked edges of the wound. 

If a cross-section is made through the excrescence of a closed canker, 
approximately the following picture is found. 

We see (Fig. 135) the whole large swelling divided radially into two 
groups by the split (sp) with its roll-like edges. This cleft forms the inner 
continuation of the outwardly recognizable funnel-like depression on the 
flattened top of the canker excrescence (Figs. 134, 135 t). At the bottom 




Fis". 13'). Cross-section through ;in apple branch with a knot of "closed canker." 



of the cleft usually lies a brown, mealy, or putty-like mass which is found 
to consist of humified cell remnants. The edges (r) of the cleft are also 
strongly browned. They are formed by thick-walled, parenchymatous-like 
porous cells, provided with a dead, brown content. The further back one 
goes from the edges of the cleft, or the point of dying, toward the healthy 
tissue of the trunk, the less noticeable is the brown color. The tissue be- 
comes white and is formed of parenchymatous wood which contains an 
unusual amount of starch, (iroups of strongly refractive cells gradually 
appear in these masses of parenchyma wood. They are clearly elongated, 
thick-walled wood cells which, isolated at times, or in small groups, appear 
irregularly distributed in the parenchymatous wood. (Fig. 135 h). Com- 



589 

pare the cross-section ^iven in Fig. 132, due to an artificially produced frost 
split on the branch of an apple tree. Parallel with the appearance of the 
first wood cells is that of the hard bast cells (Fig. 132 h b) in the bark. 
These prosenchymatous elements in the edge of the wound, formed of 
parenchymatous wood, are the initial stages of the normal annual ring for- 
mation and extend from the edge of the wound backward, approaching one 
another more and more closely, until they have united in a normal annual 
ring on the healthy side. If we start with the normal annual ring zone on 
the healthy side of the trunk, we may thus conceive this formation as 
follows; it is ,as if the prosenchymatous tissue of a healthy annual ring 
(Fig. 135 c h) had been divided into several radiating branches (Fig. 
135 h) within the canker excrescence which chiefly consists of parenchyma 
wood, rich in starch and containing here and there large crystals of calcium 
oxalate. {Radial diz'ision of the annual ring.) 

The edges of the wound, themselves, are not found united; the cleft. 
therefore, in spite of its narrowness, has never completely coalesced since 
the outermost cells, edging the cleft, constantly die. 

In proportion to the uncommonly luxuriant new formation, the number 
of dying cells in "closed canker" is very small. The dead place here always 
forms only a narrow twisted cleft; while in "open canker" the originally 
dead tissue represents a broad surface and the dying back of the edges of 
the wound extends so far that not only the wood surface which first remains 
uncovered, but also each overgrowth edge is incompletely covered by the 
succeeding one. 

The characteristic radial division, or splitting of an annual ring (Fig. 
135 nh, h) within the \\oody. parenchymatous edges of the excrescence is 
less conspicuous in open canker and may completely disappear in case the 
entire trunk, which has remained healthy, participates, at the height of the 
canker-wound, in the exorbitant thickening, i. e., excludes a one-sided hy- 
pertrophy of the trunk. 

The determination of the dry substances in normal and cankerous 
wood in the cherry gives a proof of the softness of the tissue in the canker 
excrescence. Normal wood has 66.9 per cent, of dry substances; the 
overlying canker wood, only 45.1 per cent. 

From the fact that the canker excrescence frequently exceeds consid- 
erably the thickness of the two or three year old branch which bears it, we 
may conclude that the excrescence which is never found on the green shoot 
of the current year, i. e., begins only in the woody twig, must grow very 
rapidly. With such rapid development of the tissue, it is not surprising 
that the fluctuations between cloudy, wet weather and periods of drought 
can so manifest themselves that, within one summer, alternate zones of 
thin-walled and thick-walled wood are produced in the canker excrescence. 
This is found if the darker zone, extending from the pith (m) in Fig. 135, 
is traced further. It corresponds to the thick-walled wood elements and, 
in the normal part of the trunk, indicates the autumn wood in contrast to 



590 



the more abundant spring wood but always within the canker excrescence 
prosenchyma v\oo(l in contrast to parenchyma wood. The illustration 
shows the last formed, dark rings in the healthy part divided radiall}- 
toward the diseased part, n indicates a diagonally cut, dead branch. 

This luxuriance of growth, 
\vhich manifests itself by the 
formation of the radiating canker 
excrescence, may not, however, 
lead uni\ersally to the conclusion 
that the growth of the tree as a 
whole is always luxuriant. On 
the contrary, a regular occur- 
rence of canker knots is found in 
weak, slender trees in certain 
localities. 

Cankered and al.so blighted 
trees usually show a very luxuri- 
ant lichen growth. At the central 
place of attachment of such 
lichen cushions it may often [)e 
proved that the cork layers of the 
branch ha\e been separated and 
the thallus cords shox'ed in be- 
tween them. In fact I could 
observe cases in which tlie lichen 
thallus penetrated the whole pro- 
tect i\e cork layer of the branch 
and reached the collenchvmatous 
bark cells, some of which still 
contained chlorophyll. The lichen 
growth may, therefore, not be as 
injurious as the yellow and green 
forms are generally declared to 
be. How much, however, the 
s[)read of the lichen depends upon 
some individual peculiarity of the 
tree is still unknown to us (j:)rob- 
abl_v a greater tenderness, poros- 
ity and torn condition of the 
bark), as is explained by an obser- 
vation on grafted older trunks of BVaxiniis. The stock, possibly one to one 
and a half meters tall, appeared only scantily covered with lichens while 
the grafted scion, which at times bore a 1.2 to 15 year old crown, was closely 
covered by lichen growth. As a rule, cankered places on old ash trees, 
standing on wet ground, are covered with lichen. 




13(3. .Juvenile condition 
cankei'. 



of tipple 



591 



In regard to the juvenile condition of cankered places, I mentioned 
under Frost Tears that I considered such small tears to be the initial stages 
of the canker excrescences. In the adjacent picture I give an illustration 
of two branches in natural size, as T found them on an apple tree, suffering 
from canker. In Fig. 136 a is shown an oval depressed part of the bark 
near a bud. The growth which took place after the injury has so in- 
creased the tension at the dead spot that the dry bark at its centre has split. 
At b we see a somewhat further advanced stage. The dead bark in the 
middle of the wound has already been raised by the overgrowth edges, ap- 
pearing at the side and united with one another. The places indicated at c 
and c' in Fig. 136 show conspicuous, protruding knots, with a uniform new 
bark covering. At r are the dried scaley, somewhat 
distended edges of the primary bark of the branch, 
which has been ruptured by frost. In this, the places 
are not near a bud ; c is in the middle of an internode 
and c' on the side opposite the bud. In Fig. 136 a? 
the wound has attacked the tissue surroundmg a 
bud. The bud is dead and the region depressed. 

The wound surface is here very great, the bark 
r'. under which air has penetrated, is still connected 
with its health}^ surroundings and that newly pro- 
duced on the edge of the dead spot has caused a 
widening of the branch, as is very frequent in blight 
wounds. 

Reproductions of oi)en canker of the ap[)le tree, 
as well as closed canker, show that the region of the 
trunk, bearing buds or young sprouts, is preferred in 
the formation of canker. .Such a preference of the 
region below a short twig is shown in the adjacent 
figure of a small pear branch (Fig. 137). Directly 
underneath the short twig at a we find a deep, already 
overgrown frost tear. At b, the region of the short- 
ened branch ring \\ ith its short internodes and many 

weak buds, the bark has been split by many small tears and dried like scales. 
The young, upper part (r) of the branch has remained healthy. In such 
bark splits frequently the strongest overgrowth edges are found which often 
represent a single enclosed knot covered with uniform bark, but having often 
two lip-like excrescences touching one another and usually running longi- 
tudinally. Such wound edges at times appear folded toward the twisted 
central cleft, the original bark tear, from there falling away ; they then 
resemble the canker ^vounds. The bark tears do not always represent 
longitudinal clefts and, accordingly, the overgrowth does not always occur 
in the form of two protruding lips but rather as knotty, spherical elevations 
with a crater-like central depression. On a branch 9 mm. thick, 1 found 
canker knots 1^ mm. high and 35 to 45 mm. broad. Other branches, just as 




Fig. 137. Preference 

shown by frost for 

the base of the 

branch. 



592 

thick and two years old, at times sliowed only very weakly callused, uni- 
formly closed protuberances, covered with new hark, which break out from 
the cleft in the old bark. 

The studies here cited determine that each canker spot has, as its 
initial stage, a wound which extends as a narrow radial tear into the cam- 
bium and kills it slightly back from both sides. This wound must be 
produced shortly before, or at the time when the trunk of the tree develops 
the greatest growth activity, since the wound surface will attempt at 
once to form a covering by means of very luxuriant overgrowth edges. 
The luxuriance of these overgrowth rolls manifests itself in the fact that, 
especially in the closed form of canker, a partition of the annual ring 
usually occurs, the edges of which chiefly consist of parenchyma wood. 
The edges of the wound are very susceptible because of this porous struc- 
ture, so that they succumb with ease to injurious attacks. 

We must consider frost as the cause of these forms of disease because 
it has been possible to produce, by the action of artificial frost, the same 
initial stages as are found in canker wounds. 

However, a number of \er\ reliable observers have determined that it 
is possible by the injection of a (capsule) fungus, Nectria ditissima\ to 
produce wounds, the forms of which resemble perfectly those of the open 
canker of the apple. I can confirm these statements by my own experi- 
ments. One has indeed a right to speak of a fungous canker but the above 
named parasite is not able to attack an uninjured axis. It can spread de- 
structively only if it gets into a bark wound. All inoculation experiments 
agree in this. On the other hand, the same Nectria is found in apple trees, 
beeches and other varieties of deciduous trees without causing any canker 
excrescences whatever. Therefore, it cannot be termed the specific inciter 
of canker excrescences but will give rise to these only occasionally when 
very definite secondary conditions co-operate simultaneously. Besides the 
presence of a fresh wound surface, it depends also upon the specific pecu- 
liarity of the tree, i. e., the cultural \ ariety, which must possess the ability 
to respond to the wound stimulus with quickly developing, very luxuriant 
overgrowth. 

This ability is so typical that in general practice one speaks of 
"Varieties with a canker tendency." Besides this, experience has shown 
that the tree easily becomes cankered in certain places and kinds of soil. 
These are the so-called frost holes, having a marshy soil consistency, an 
impervious sub-soil, etc. 

These are well-established facts. If we now keep in view the fact 
that Nectria ditissima must have some wound for infection, we must ask 
whence came these wounds. From observations made in nature and from 
the results of experiments with artificial frost, we are convinced of neces- 
sity that frost injuries are the most easily accessible. Paparozzi holds to 



1 See literature in the second volume of this manual, p. 209. 



593 

the same standpoint for the canker of pear trees'. If the frost wounds are 
flat surfaces such as will be found later under "Blight," the Nectria will 
infest the tree without its formation of luxuriant overgrowth edges. If, 
however, narrow frost tears, extending into the cambium, are produced 
into which the Nectria find entrance, the tree responds with the formation 
of canker excrescences in case climate, habitat or specific characteristics 
make it capable of so doing. 

Accordingly, the fungous canker also appears to be essentially depend- 
ent upon frost injury and its combatting or avoidance will have to be 
carried on with due consideration of the dan<jer from frost. 



b. Crotch Cankkr in Fruit and Forest Trees. 

"Crotch canker," which is of frequent occurrence in forest and fruit 
trees, should be mentioned as an especial form. It 
consists of frost wounds found at the bases of the 
branches, or twigs, which belong to the group of 
open cankers and are formed from black, dead 
surfaces differing in size with luxuriant, irregular 
overgrowth edges. The angle where the branch 
joins the main trunk is separately attacked in 
many varieties. In the so-called "bifurcations," or 
forkings, where the difference between the main 
and the lateral branch disappears so that two equally 
strong branches grow out from one point, the ex- 
posed and blackened place in the wood is usually 
elevated at both sides and, accordingly, the over- 
growth edge is formed from the material of both 
l)ranches (cf. Fig. 138). Aside from the more 
sensitive, imported trees, our indigenous forest 
trees, according to Nordlinger-, are also exposed to 
injuries at the crotch, especially when young; thus, 
for example, beeches in shady positions and on poor 

soil, in which the internodes at some distance from the crotches are also 
often covered with frosted surfaces. The annual growth of the oak also 
suffers on poor soils and the ash is found to be injured if the tree stands In 
depressions with a heavy clay soil. In such damp places I found the over- 
growth unusually luxuriant but so covered with thick, split bark, overgrown 
with lichens, that it had become irrecognizable. 

Opposed to the theory, which Hartig represents, that crotch canker is 
conditioned by spring frosts, Nordlinger thinks the cause is frost at the 
beginning of winter. He bases his opinion on the investigation of the wood 
ring and on the fact that, in thousands of cases, crotch canker is very 




\P\ix. 138. Crotch canker. 



1 Paparozzi. G., II cancro del pero. Roma, Offizina poligraflca; cit. Bot. Cen- 
tralbl. 1904, v. XXVIII, p. 94. 

- Die Septemberfroste 1877 unci der A.stwurzelschaden (Astwurzelkrebs) an 
Baumen. Centralbl. f. das ges. Forstwesen. Wien 1878, Part 10. 



594 

abundant high up in the crown and in shady places, i. e., those less exposed 
to spring frosts. 

The especial susceptibility to frost of the base of the branch is ex- 
plained by the fact that, on account of the greater number of buds originally 
set there, more parenchymatous medullary bridges are present, which 
traverse the wood ring. The parenchymatous wood is more tender and 
contains more starch. To this should also be ascribed the fact that bark 
beetles like to settle in the crotches and that wood mice, as Nordlinger 
states, frequently eat only the base of the lateral branches in poplar suckers 
(Popidus monilifera) . Therefore the frost, i. e., the spring frost, kills the 
base of the branch most easily. 

In old, weakly growing trunks, the luxuriance of the overgrowth 
edges decreases considerably and can become so slight that only narrow, 
circular overgrowth edges are present, which push out slowly from under 
the dead bark. This blight corresponds to that of the crotch injury, since 
in open canker, the first stage is not a cleft but a collapsing, drying dead 
bark surface. Hence, the expression "crotch blight" frequently used by 
many practical workers. 

c. Canker on Cherry Trees. 

In sweet cherries are usually found semi-cylindrical protuberances on 
the twigs, or older branches. The outside of these swelUngs, often thicker 
than one's fist, not infrequently seem depressed, as in blight; the dead 
bark is split and partially stripped from the blackened wood body, still 
remaining attached as larger scales with up-rolled edges (cf. Fig. 139). 

The barrel-shaped swelling on the branch represents an abnormal de- 
velopment of the overgrowth edges (u and u') of the wound (sp) which 
does not close entirely, as is also found in the "closed canker of the apple." 
In the latter, however, the overgrowth tissue is a sudden, unusually lux- 
uriant widening of the annual ring, while, in the cherry, the swelling of the 
normal side of the twig shows a gradual transition to the excrescent over- 
growth edge. On this account, the closed canker of the apple has the form 
of knots but the completely developed canker of the cherry a gradually 
increasing barrel-shaped thickening. Besides this typical form, various 
transitions are found from the closed canker knots, on the one hand, to 
the flat wound, on the other, which is termed blight. 

Conical swellings are found at the base of older branches of trees, 
suffering from canker, which can offer all the transitional forms up to the 
typical canker swelling. The initial stages are found on one side of the 
branch in the form of a small frost wound alongside the first annual ring. 
An especial emphasis should be laid here on the fact that the enormous 
overgrowth tissue seems often to be developed from a medullary bridge. 
This, therefore, points to some direct injury to the bud. The development 
of the overgrowth edges is continued in subsequent years, when only paren- 



595 



cliyma wood is formed in which starch is rapidly and aijundantly de[)osited. 
If the canker swelhng has become considerably extensive, the branch dies, 
as a rule, above this swelling; in this, stroma-forming fungi (usually from 
the family of the Valseae) greatly co-operate. They appear in the form 
of small warts. 

If the young branches (i to 2 years old) of trees suffering from 
canker are examined, blight-like places, often several centimeters long, are 
found, with lip-like overgrowths instead of individual buds, while, on the 
parts of the branch above and below 
these places, the buds have developed 
to short shoots. It is evident from 
this that the injury to the branch 
must take place before the breaking 
of the bud. 

Since, however, no injury of any 
kind can be ascertained in the year in 
which the branch is formed, but will 
be found only in the following spring, 
it must have arisen in the winter or 
at the beginning of spring; the as- 
sumption is, therefore, pertinent that 
the bud. as it unfolds in sprouting, is 
killed by the frost and that the accu- 
mulated plastic material is now used 
in the formation of the excrescent 
edges of the wound. Since the tissue of 
these overgrowth edges remains as 
soft as the parenchyma and is almost 
always found filled with starch, it \i 
clear that, in the following winter, its 
edges succumb very easily to injury 
from frost and new excrescences are 
produced from the deeper lying zones 
which remain healthy. A consider- 
ation of the cross-section in Fig. 139 
makes clear the whole process. This 
shows that the clefting of the axis 

has begun at a short distance from the pith body (m) and in the 
second annual ring. The third annual ring has already furnished 
luxuriant overgrowth edges (/) which, in turn, split the following year 
(sp'). These secondary clefts cause secondary overgrowth (/'). The 
barrel shaped canker swelling, however, is formed chiefly by the ex- 
crescen: wound edges of the main cleft, which are radiatingly arranged 
{k). Thus an annual ring inside the canker swelling is divided into 
several rings, as in the closed canker of the apple. The bark body 




Fig-. 139. Chen-y canker frost cleft 

with overgrowth edges in longitudinal 

view and ci'oss-section. 



596 



(r) also forms corresponding excrescences and, in places, develops thick 

bark scales. 

In the canker of the cherry, as in all canker diseases, only scattered 

individuals are found diseased in large plantations. I often found in the 

healthy shoots of these cankered examples 
abnormally broadened medullary rays, a phe- 
nomenon which may be observed also in 
other kinds of trees. I, therefore, surmise 
that the inclination to become diseased i<'ith 
canker may be found in the individual ten- 
dency toward a widening of the medullary 
rays. 

The Cankkr (Scab) of the Grapevine. 

In the older wood of grapevines near 
the surface of the soil, about lo to 50 cm. 
above it, are found scattered, small spherical 
or large barrel-shaped, out-pushings of the 
wood from the bark, with a beady, irregular 
upper surface, split lengthwise into fibres. 
Fig. 140 shows a beady canker swelling 
between the strips of bark which are drawn 
in white. In small, isolated outgrowths, their 
production, according to Gothe's^ investiga- 
tions, is clearly recognizable as the over- 
growth tissue of longitudinal clefts. The 
clefrs appear at the edge of the annual ring, 
from which it must be concluded that they 
were produced at the time when the de- 
velopment of the next annual ring began, 
caused by the dying back in spots in the 
cambial zone in the spring. In regard to the 
production of the excrescences, I have stated 
some diiTering observations of my own, 
under the head of the disease to be treated 
next, — Canker of the Spirea. 

The injury, which killed the cambium, 
has also caused a considerable circular sur- 
face on the old wood to turn a deep brown. 
The overgrowth beginning at the healthy 
place, which often quickly closes the cleft, is characterized by an excrescent 
luxuriance of the Avood and bark. The woody edges, curling out towards 
one another, consist of soft, ductless parenchyma wood, without any real 




Fig- 



140. Canker excrescences 
in the grapevine. 



1 Mitteilungen iiber don schwarzen Brenner und den Grind der Reben. Berlin 
und Leipzig:, H. Voigt, 1878, p. 28 ff. 



597 

prosenchymatous elements, i. e., they exhiliit the characteristic structure 
of the excrescent wound wood. If the overgrowth edges have united into 
a connected annual ring, this grows further in such a way that it is sub- 
divided by medullary rays. The direction of these medullary rays continues 
that of the medullary rays of the wood formed the previous year. There- 
fore, this wood has undergone only a temporary interruption in the brown 
dead tissue. 

The changes and tissue excrescences descril)ed are never found in 
wood of the current year. 

Gothe thinks the bead-like appearance of the tissue excrescence, which, 
growing extensively radially, splits the old bark, is explained by a complete 
"overlapping, in\\ard growth" of the overgrowth rolls, wdiich are present 
most abundantly at places on the vine lying about 30 cm. above the surface 
of the soil. Examination shows that, starting at such places, the number 
and extent of these swellings decrease away from as well as towards the 
soil ; close to it, and about one meter away from it, they occur very rarely. 
With a slight development of the disease, the attacked trunks may vegetate 
for several years and then still produce bearing wood. With a greater 
de\elopment of the canker swelling, the wood, lying above it, dies. 

The rapidity, with which the canker swelling is produced, is proved by 
the fact that, on August 8th, plants were found in which the grafting tape 
lay embedded 0.75 cm. in the tissue excrescences. Therefore, the entire 
canker swelling, 2.5 cm. thick, can only have been produced after the time 
of grafting (in May), for it can not be assumed that a scion would have 
l)een inserted in a diseased vine. 

Gothe has proved by the following experiment that the injuries to the 
cambial ring take place in the spring. In April, when the vines were 
])runed, 12 strong bearing vines were tapped, between two nodes, with a 
dull iron, in such a way that an injury to the cambial layer could be as- 
sumed. Glass tubes were then shoved over the injured places and the 
openings closed. The first traces of the swellings could be proved as early 
as June 8th, while on specifically scabby vines the tissue excrescences did 
not appear until June 20th. Up to autumn, perfectly normal scab struc- 
tures continued to form in the glass tubes, with also the same anatomical 
structure as naturally formed excrescence edges. 

Spring frost may be considered as the cause of these excrescences in 
nature. Most of the literature which proves the appearance of grape 
canker after spring frosts also favors this assumption\ It is also strength- 
ened by the discovery that grape canker occurs only in the so-called frost 
holes. Gothe cites in this connection, an example from a \ineyard which 
l)egan on a small slope, passed through a hollow and rose again on the 
opposite slope. On both slopes the plants were healthy, but in the hollow 
were found to have been attacked by the disease. In a subsequent test, the 



1 Giithe cites v. Babo, Weinlmu, p. 305: Dornfeld, Weinbauschule, p. 129, 
Kohler, Der Weinstock und dvr Wein, p. 20".; du Breiiil, I.es Vignoliles. 



598 

observer found that the disease had occurred on 20 other vines, which stood 
in depressions in the soil. 

The fact that the grape canker appears at a definite height on the vine 
is explained by the various differences between the heat maximum and 
minimum to which the vines, at different heights, are often exposed at the 
time of spring frosts. 

Draining of the soil might prove the most effective method. Kohler 
has already announced favorable results in his above-mentioned works. 
Besides this, attention should be given to the planting of hardier varieties 
and especially the choice of suitable positions (moderately moist, porous 
and warm soil). 

It is not inconceivable that the scab, without the action of frost, may 
f)e produced by an accumulation of plastic materials, as Blankenhorn and 
Miihlhauser believe they have observed as the result of too severe cutting 
back'. It is certain that the beginnings of the swellings, occurring in the 
form of medullary ray excrescences, can appear in the vines in which in 
the spring the bark has been raised in places from the wood of the previous 
year. Such canker excrescences, as said above, can mature without any 
injury from frost, just as canker-like, excrescent overgrowth edges are 
found in luxuriantly growing pomaceous varieties. But in such cases, the 
deep, extensive browning of the wood body is lacking. 

c. Canker on Spiraea, 

A disease, not yet described, showing great relation to the canker oi 
the grape, attacks the bases of the stem of Spiraea opulifolia. The disease 
seems to occur more commonly only in regions with very cold winters. The 
material which I had for observation came from East Prussia. 

Other wood, at least two years old, with strong annual rings shows at 
the stem bases unusually abundant hemispherical swellings of the wood, 
scattered, or in rows like chains of beads, or in masses. (Fig. 141 A, k, 
kk). The size of these swellings varies from a few millimetres up to 1.5 
to 2 cm. in diameter. The swellings are brown, darker than the outermost 
bark layers, which they rupture, and loosened in tatters. They are often 
cleft or depressed in the centre like a funnel and provided with thick granu- 
lated, torn surfaces. No single bark layer can be raised, since the tissue 
of the swelling is brittle and easily breaks off in pieces. 

In cutting away a considerable swelling, or, as one is justified in saying, 
canker knot, it is found that lamellae or firmer material radiate out from a 
more or less broad base. However, the lamellae neither extend through 
the whole thickness of the canker, nor are they separated sharply from the 
tinder-like, decayed, darker ground tissue. This itself is to be considered 
an excrescent continuation of the last annual ring, which becomes more 
and more delicate toward the periphery. 



1 cf. Wlirzburger Weinbaukongress. 




Fig. 141. Canker on Spiraea. 



6oo 

In Fig. 141 B, which gives a cross-section of tlie canker knot {k) from 
Fig. 141 A, m indicates the pith body; a. the uninjured annual ring of the 
hrst year's growth; b^ the cleft ring of the second year; c, the wood of the 
third year, which is growing out into the canker swelling {k) ; i represents 
the firmer tissue islands and stripes in the tinder-like ground tissue. 

In the cases which have been observed up to the present, the main part 
of the canker knot has seemed to be the production of a single year and, in 
fact, a one-sided woody excrescence over a place which, even in the pre- 
\ious year, had formed a wedge-shaped zone of porous, parenchymatous 
wood tissue, its pointed end toward the interior. In so far two years are 
necessary for the completion of the canker knot. If the above mentioned, 
wedge-shaped zone is traced backward to the annual ring of the previous 
year, it will be seen that this originates in a brown, slender place in the first 
spring wood. 

The adjoining anatomical picture, Fig. 141 C, will facilitate the expla- 
nation. The whole figure C is a radial section of the second annual ring 
from a Spirea stem and contains the tissue zone which is preparing to 
develop into the real canker swelling. The line f to ff represents the strip 
of changed tissue, which in its further development in the following year, 
will have become a complete canker knot. The tissue shown at a is the 
autumn wood of the first annual ring. No disturbance has been observed 
in the wood body of this first annual ring, just, as in the canker of the grape, 
the first annual ring has a perfectly normal structure. The wood of the 
second annual ring (b) at first began a normal development and continued 
it up to b\ 

At this time occurred some disturbance which produced the cleft (d). 
and browned its edges (c'). The time this split was produced must have 
been that of the greatest formation of new wood for, only a few cell rows 
farther, we find that the split is closed at h, and the annual ring has grown 
further with the formation of groups of normal parenchymatous elements 
(p). Only a single cell-row (k) forms a radial stripe, with shorter cells 
containing wider lumina. Now the abnormal wood stripe, instead of dis- 
appearing as the annual ring matures and increases in width, grows broader, 
since more and more cells take part in the changed form of construction 
(kk). Thus the disturbance advances until the second annual ring is fin- 
ished and then begins, to a renewed extent, in the spring zone of the third 
annual ring (c-c). 

Even when the second annual ring is finished, the stripes of the begin- 
nings of the canker may be seen to project as slight elevations above the 
periphery of the remaining wood ring. In the spring of the third year the 
new formation at this place is so luxuriant that the rapidly growing canker 
knot, strengthened by the equally rapidly excrescent part of the bark (k I), 
ruptures the normal bark (r) at sp and now grows further, as it were, as 
a foreign structure, in order, after some weeks, to end its growth, being a 
complete canker knot i to 2 cm. thick. 



6di 

Similar formations are found in the canker of the (jrapc. Only I have 
found as yet that the disturbance, setting in at the beginning of the second 
year, and corresponding to the holes (d), consists of a broader tangential 
elevation, circular in form. It give the impression that, at the beginning 
of the period of growth, the bark was raised from the wood body for a 
considerable distance. My repeated experiments with artificial frost show 
that this process can actually occur and, in fact, it is met with rather fre- 
quently in various trees. As a result of this lifting of the bark, a tangential 
hole is produced on the grapevine, usually at the place where, on Spirea, 
the slender, radial cleft is found. The raised bark forms, first of all, wood 
parenchyma and this soft wood body passes over very gradually, in the 
course of the following summer, into normal wood. Here, however, some 
of the broad medullar}^ rays are found abo\^e the raised part which have 
developed especially and at the end of the year project as delicate tissue 
caps. 

In the grapevine, as in Spirea in canker formation, these are not neces- 
sarily overgrowth edges, as is always the case in the canker of the apple; 
in the former, tissue cushions of a wood body which has become parenchy- 
matous develop to canker knots. These cushions at first appear uninjured 
and are at any rate caused by some previous disturbance. This explains 
the theory expressed by Blankenhorn, on the canker of the grapevine, viz., 
that the stoppage of plastic materials (for example, with too strong prun- 
ing), can cause the canker excrescence. 

The formation of the canker excrescence often indicates some modi- 
fication, inasmuch as the canker cushions, produced in the first year, are 
partially killed by the frost. Then the central, most delicate part suiifers and 
represents a black, dried core. In the following spring only the edges 
grow further, just as do overgrowth edges, and line the cleft, as is shown 
in Fig. 141 B. It has been said that the parts of the edges of the growing 
canker knot continue growing "after the manner" of overgrowth edges. 
Actual overgrowth edges, spirally curved, are found only rarely (as in the 
canker of the grape). 

Fig. 141 B shows that the wood ring of the third year passes over 
imperceptibly into the canker swellings. Therefore, the canker swelling 
is actually a wood formation but this wood, because of the enormous rapid- 
ity of the tissue formation, is a structure so soft and so similar to the 
likewise excrescent bark tissue, which is dying back from the outer side, 
that it is often difficult to determine the boundary between them. This 
porous wood, which I have found so very soft only in the canker of the 
rose, forms, on the dead swelling, the brown,, tinder-like ground mass, of 
which we spoke at the beginning. The firmer, lighter colored parts are the 
islands of thick-walled wood cells and ducts (Fig. 141 B, i) increasing in 
breadth and thickness at the periphery. In canker knots of different sizes, 
the groups of ducts (i) are sometimes found in the form of wedge-like 
lamellae, becoming thicker tow^ard the outside, sometimes (as in Fig. 14 15) 



6o2 

in the form of spherical groups with a sheath-like arrangement of their 
elements. The groups not infrequently unite and in this way cause a 
greater firmness but no complete wood ring has ever been observed. It is 
these isolated parenchyma and duct groups which in pruning so greatly 
resist the knife, that they are torn loose from their connection with the 
other tissue before being cut through. Hence the easy crumbling of the 
canker knot. 




Fig. 142. Rose Canker. Concentric overgrowtli edg-es may be recognized, rising 
UKe terraces around a central, dead wood surface. 



f. Canker of the Rose. 

In the culture of the newer climbing roses, which (according to 
Crepin-Briissel) have resulted from a crossing of Rosa Jndica with R. 
multiflora and are called Polyanthus varieties, we have become acquainted 
with a phenomenon which comes under the head of canker excrescences. 
The adjoining Fig. 142 A and B, represents such canker swellings as are 



6o3 

found at the base of the strong stems of Crimson Ramblers in Germany. 
Their appearance on the lower part of these rose stems, which, as is well 
known, grow most luxuriantly in (jermany, reminds one of the same occur- 
rence in the canker of the grapevine. As in all forms of canker, we find 
here also that the region of the axis is preferred where branches (A, a) 
are produced and the base has strongly thickened or split ojjen into curled 
excrescences (B, iib). As an explanation of this phenomenon, it need 
only be remembered that the wood ring is broken and especially susceptible 
to disturbances at that part of the normal axis where a branch starts, for 
the pith l)ody is widened at the place of insertion of the twig into a pith 
bridge, transecting the wood ring and passing over into the lateral branch. 
In such a developing branch the eyes stand closest together at the base; 
they may often be but little developed, because the leaves are still bract-like 
or incomplete, but the parenchymatous medullary bridges, which traverse 
the wood ring, are present. 

The canker spot on the main axis in the present case, as in the "open 
canker of the apple," shows a central wound surface with an exposed brown 
wood body (Fig. 142 A and B, 71'). This surface is encircled by terrace-like, 
rounded overgrowth edges (ii). These wound edges, however, do not 
retain their uniform wall-like character, as in the canker of the apple, but 
develop into irregularly knobbed, or beaded, heaped up tissue masses. In 
other cases, the canker of the rose occurs, like the canker knot in Spiraea, 
in boil-like, united and elongated wound edges, which line a long cleft, 
starting from the base of the branch. All excrescent tissues ultimately 
rupture the bark (r). 

An insight into the production of these excrescences, which are not 
exceeded in luxuriance by any other canker swelling, is obtained from 
the above reproduced cross-section of a rose stem, at the place where it has 
formed a small, isolated bead-like elevation (cf. Fig. 143). We perceive 
that the stem has developed normally in the first year; a normal wood ring 
(/?) surrounds the pith body which has Ijroad medullary rays (mst) and 
which ruptures later {z'). In the second year, as the first cell rows (gr) 
of the new wood ring were in the midst of developing, some disturbance 
must have made itself felt in the form of some break in the tissue, for the 
new wood ring (hp), for the most part, has taken on the character of the 
parenchyma wood and only in places (h') has it retained the normal wood 
structure, characterized by the formation of ducts and thick-walled wood 
cells. The cause of this breaking up of the tissue has been a split in the 
bark, traces of which may be seen in the lip-like, small indentation at the 
upper side of the figure. The cork layers (k) of the bark, which cover 
this, have been split and the overgrowth tissue (zu) swelling out from both 
sides, which has been covered in turn with a cork mantel, has coalesced into 
a closed mass in the immediate proximity of the tear (which is not shown 
in the drawing). If this tissue is traced backward toward the healthy 
(upper) side of the branch, starting from the most luxuriant place of 



6o4 

excrescent tissue (^c), it is found that this gradually dwindles away and 
inside the bark begins to take on a normal character (/(/.) Here the ar- 
rangement of the hard bast cords is still approximately normal but their 
structure has been changed greatly. The majority of the bast cells have 
a yellow, swollen content and easily browned walls. Nevertheless, they 
are distinguished, as strong, light-colored groups from the deep brown bark 




Fig-. 143. First stages of tlie rose canker. 



parenchyma which is cut off from the outer collenchymatous bark layers 
by the subsequently produced layer of plate cork (k'). 

The drawing shows, however, that the ring of bast cells (b) is removed 
farther from the wood body the further it advances into the tissue of the 
excrescence. It is, therefore, pressed away from the wood body by the 
increase of this body. At the same time the bast ring is seen to have been 



005 

pushed back further from the outer collenchymatous Ia)'ers. Therefore, 
cell increase must have taken place in the primary bark. 

The question should now be asked as to whether the tissue, which 
presses the bast ring away from the wood, is exclusively a product of the 
secondary bark or whether the wood cylinder itself has contributed to this. 
We find the answer in the tissue group {hp') which represents the paren- 
chyma wood. We find such groups of parenchymatous wood within a soft, 
thin-walled tissue, when hark wounds are healed by the formation of new- 
tissue from the youngest sapwood layers, remaining on the wood body. We 
learn further, by studying the false annual ring (cf. False Annual Rings) 
and the healing processes of inner frost tears, to recognize the formation 
of parenchyma wood from the broken sap wood layer. Also, in the pro- 
cesses of grafting and especially those of budding and bark grafting we 
find that cicatrization tissue has been formed from the youngest sap wood, 
if the actual cambial zone has been injured. If the cambium is retained in 
an injury but the bark mantle is broken by a tear in the bark, the cambium 
develops into a tissue, at first parenchymatous, which, at the edge, gradu- 
ally passes over into a normal wood structure, according to the amount in 
which the normal bark pressure is restored (cf. Wound Healing). 

The same new growth can also take place on the inner iide of the bark 
if this is raised from the wood cylinder without an entire interruption of 
its nutrition. T have carried out the experiment with cherries in such a 
way that the still smooth bark of the young trunks was loosened in strips, 
connected at their upper ends with the uninjured bark mantel left on the 
axial cylinder. At the places where the upraised strips passed over into 
the uninjured bark, I found the same callus formed on the inside which 
later was differentiated into bark and wood. It has therefore been deter- 
mined experimentally that exposed wood can produce new bark and that 
upraised bark tatters can produce new wood when still attached at their 
upper end to the wood body. 

In this w-ay, the process in rose canker becomes easily understandable. 
In the first spring, a tear appears in the bark which extends to the cell rows 
of the spring wood of the new annual ring already formed and results in 
the lateral raising of the bark from the cambium as shown in the holes (/). 

At first the constricting influence, which the cork girdle (k) usually 
exercises on bark and young wood, is wholly overcome because of this cleft, 
wliich results in a luxuriant increase of the young wood (on the under side 
of the figure) where the cambial zone has not been destroyed, and the lux- 
uriant increase of the parenchyma of the inner bark where this had been 
raised from the young wood (at / on the upper side of the figure). The 
new structures, whether formed from bark tatters, or young wood, are 
uniformly callus-like and pass over imperceptibly into one another. It is 
these new structures which have ruptured the previously continuous bast 
ring {b, b'), have pressed outward the most strongly injured part (b') and 
caused its death after splitting it off from the outer bark. 



6o6 



The main question is, in what way can the first radial cleavage have 
taken place. And the only answer to this can be ; as the result of frost. 
For we again find here the browning of the pith crown, the tearing and 
widening of the medullary rays, the phenomena of elevation and cleavage 

of the tissue which I have been 
able to produce experimentally 
by the action of artificial frost. 
Only, I have not been able to 
produce artificially the secondary 
phenomena, viz., the luxuriant 
tissue increase. This probably 
is based upon the fact that in 
using artificial frosts I have not 
yet found the proper juvenile 
developmental condition. This 
must be the time when the cam- 
bial activity has just begun, as is 
evident from the small number 
of cell layers just formed by the 
new annual ring. If the dis- 
turbances occur later, capacity 
for reaction in the tissue is less 
and the excrescent cell increase 
does not take place. Gothe's ex- 
periments show how very deter- 
minative the time of injury is. 
As already mentioned, he pro- 
duced excrescences resembling 
the canker of the grape, by a 
continued tapping of the grape- 
vine in the early spring. The 
grape canker is closely related 
ontogenetically to the canker of 
the rose. 

g. Canker of the 
Blackberry. 

It is a noteworthy fact that, 
with the exception of grape 
canker, all the other canker ex- 
crescences are found in the family of the Rosaceae. In the canker of the 
blackberry, cauliflower-hke, hard, gfistening, white tissue masses with a 
beaded warty surface are produced on the older wood (cf. Fig. 144 k). 
These tissue masses sometimes form isolated spheres ; sometimes collect in 
elongated, wart-like cushions, as in Spiraea. The region of the eye is the 




Fig. 144. Canker of the wild blackberry. 



6o7 

preferred place of production. The bark is split and partially thrown back 
like wings. 

With an abundant appearance of the canker swellings, first of all, the 
foliage turns yellow, then the stem begins to die back slowly from the 
browned eyes. By July, as a rule, the diseased branches on the same 
shoot, side by side with bright, perfectly green ones, have died back entirely. 

If healthy plants are examined for such cankered stems, either small 
reddish, or brown, long ridges are found, or gaping tears often one centi- 
metre long. I observed the same phenomenon also on many petioles. The 
sloping edges of such tears are covered also with cork. On these edges, 
small beady excrescences appear in places which consist of parenchyma and 
are formed from the primary bark close to the outside of the hard bast 
cords. 

In the Rosaceae this tissue region proved to be extremely easily stimu- 
lated. I found that, after very dififerent injuries to the bark, which gener- 
ally did not extend to the hard bast, strong branches responded to the 
wound stimulus by a parenchymatous increase close outside the hard bast 
cords. Often, in the canker of the blackberry, a place of predisposition for 
the formation of canker may he noticed, for, in the spots where a wart-like 
excrescence had appeared, even in young branch shoots, the mechanical 
rings formed from the hard bast cords and other thick-walled connective 
elements are proved to be unthickened. A thin-walled parenchyma had 
appeared instead of the prosenchymatous and sclerenchymatous tissues. 

The parenchymatous, excrescent tissue in the primary bark increases 
very rapidly and ruptures the overlying normal bark layers. In the interior 
of the canker wart, a porous wood body is formed which is rich in ducts. 
The formation of wood elements is repeated in the peripheral parenchyma 
layers of the excrescence zone first produced since meristematic aggrega- 
tions arise from which develop tracheal wood elements, arranged like bowls 
or shells. 

The beginning of canker in the blackberry therefore is a parenchy- 
matous excrescence in the primary bark body which grows outward, with 
a caulitlower-like ramification. Only later does the tendency to hyper- 
trophy extend backward into the inner bark, finally attacking also the wood 
ring which, at first, seems to have a normal structure. As soon as the 
swellings become older and the wood body participates in their formation, 
it increases to 3 or 4 times its normal size. We find similar processes in 
dropsy, in the formation of tuber-gnarl. etc. The canker is more rare in 
Rubus ; as yet I have found it only in four cases and always in narrowly 
restricted places. 

Corresponding Features in Canker Swellings. 

In a survey of all the known material relating to closed canker corre- 
sponding features are found. ("Open canker" forms a transition to blight 
and is included here). The production of a small tear forms universally 
the beginning of the disease. It may be seen in all cases that the injury must 



6o8 



have taken place in the early spring and that the richly collected material 
enabled the parts surrounding the wound to form enormous excrescences 
most quickly. The parenchymatous character of the new structures causes 
a great sensitiveness to injurious atmospheric influences and especially to 
frost. LoW' temperatures, therefore, are able to injure the canker tissue in 

the next period of growth. The injured 
tissue complex can respond repeatedly with 
excrescent tissue, because, with its paren- 
chymatous nature in the previous period of 
growth, it has stored up ver\' abundant re- 
ser\e substances in the form of starch. 

The canker forms in the individual 
genera of the Rosaceae difi^er only in the 
manner of reaction to the wound stimulus 
and agree in that they prefer the bud and 
its immediate surroundings as the place of 
production. The reason for this may be 
souglit in the division of the trunk at the 
place of insertion of a bud. The wood 
ring is always more slender here and finally 
tra\'ersed by a parenchymatous pith bridge. 
The initial stages of the canker knot, 
so far as observed, i. e., the small tears 
usually arising near the buds, have been 
produced by artificial frost, but not the 
luxuriant overgrowth structures. This cir- 
cumstance may possibly be traced back to 
the fact that a period in the spring had 
been chosen which was too late for the 
action of the artificial frosts. 

Tn the healthy branches of cankered 
trees an abnormally increased formation of 
the medullary rays has often been observed, 
and this may indicate the explanation of 
the tendency to canker excrescences of 
certain cultural varieties, or different indi- 
viduals in certain habitats, since those ex- 
amples will answer most easily to a wound 
stimulus by hypertrophy, if their medul- 
lary, or rather bark rays, grow luxuriantly 




Fi 



145. Fro.st spots on pear 
bark. 



in a healthy condition. 

Bligkt (Sphacelus). 

In contrast to the term "canker" which in general practice is used for 
the heterogeneous phenomena of a gradually extending disease, one under- 
stands pretty generally by the term "Bliylii" the occurrence of dead, black- 



PART VIII. 



MANUAL 



OF 



PLANT DISEASES 



BY 



PROF. DR. PAUL SORAUER 



Third Edition— Prof. Dr. Sorauer 

In Collaboration with 

Prof. Dr. G. Lindau And Dr. L. Reh 

Private Docent at the University Assistant in the Museum of Natural History 

of Berlin in Hamburg 



TRANSLATED BY FRANCES DORRANGE 



Volume I 
NON-PARASITIC DISEASES 

BY 

PROF. DR. PAUL SORAUER 

BERLIN 



WITH 208 ILLUSTRATIONS IN THE TEXT 



5373 
.S6 



Copyrighted, 1917 

By 

FRANCES DORRANCE 



7 



yj 



©CU479859 



THE RECORD PRESS 
Wilkes-Barre, Pa. 



JAN -5 1918 



6o9 

ish, extensive spots in the bark which have dried on the wood. In smooth 
barked trees, instead of large, connected blighted surfaces, numerous small 
depressed places in the bark are noticed, appearing often on one side of the 
tree. These resemble finger marks and are usually called frost plates. 
These injuries are abundant, or scarce, according to the susceptibility of 
the variety to frost and the conditions of the places of growth. In stone 
fruits, the phenomena of blight are found most frequently in cherries and 
plums ; in the more sensitive peaches and apricots, the trunk usually suffers 
as a whole. 

In pomaceous fruits, pears undoubtedly tend most easily to injuries 
from blight. Of forest trees, the beech and oak count as especially sensi- 
tive and in damp places the ash and acacia also. The edible chestnut is 
found in central Germany only in isolated localities. Among conifers, the 
fir seems more sensitive to frost than the spruce. The larch suffers as soon 
as it lacks sufficient light and air. The linden and maple are rarely found 
to be injured. Blight spots are found most rarely in the older birch, elm, 
willow, poplar, hornbean, and especially the pine. 

The dying of the bark is to be considered as a direct effect of frost. It 
penetrates to different depths and can, accordingly, produce a different 
appearance in the different blight wounds. Thus, for example, frost fre- 
quently attacks only the youngest layers of the bark and sap wood, includ- 
ing the real cambium. The older, outer layers of the bark die only from 
lack of nourishment, since the bark, killed by frost, turns dark in a short 
time after thawing. We find in the spring (especially in pears) depressed, 
sharply outlined places, often only very small in extent and at first only on 
different sides of the trees, or branches. These places soon become dry 
and adhere to the wood (Fig. 145 p). They are the above-mentioned 
"frost plates" found by many fruit tree growers. A cleft appears at the 
boundary between the dried part of the bark and the healthy part, which is 
raised up by the growth in thickness of the trunk. The dead part of the 
bark is again cut off from its surroundings by this cleft and loses its ar- 
resting influence (Fig. 145 r). 

The arrestment, exerted by such a dead place, lies in the increased 
pressure of the bark mantel so long as this bark mantel is still connected 
with the dead, dry, inelastic tissue. The bark pressure will be greatest 
near the dead places and the number of newly formed elements the 
smallest. 

We find this at the beginning of the healing processes. The tree en- 
deavors to cover the dead places by the formation of overgrowth edges 
from the healthy parts of the bark. This can take place in two ways, 
according to the kind of blight injury. If the branch, at the time of the 
frost, already has some older wood, which is browned on the blighted side 
but not split off, then the overgrowth edges often gradually push between 
the dead bark and the wood body and slowly lift the scale-like, dry 
brown mass of the bark. With each successive year, the overgrowth edges 



6io 



III 



approach more and more closely to one another from the sides until they 
finally unite, cover the blackened place in the wood and thus push out the 
previously attached bark and .throw it off. 

In Fig. 146, which represents a blighted young 
pear trunk, we see at the top, the old, blackened, 
exposed wood body which originally was covered with 
bark in a fresh condition ; it is left light in the drawing. 
The bark on the whole side of the tree has been killed 
by frost, dried up and thrown off from the healthy 
part by the overgrowth edges which appear after frost. 
The swollen place at the base of the drawing illustrates 
the broadening of the flattened trunk, which occurs 
frequently at blighted places because of the in- 
creased formation of wood by the uninjured, adjacent 
tissue. 

On thin twigs, the frost plates are often very 
small, but the wood under the dried bark is found to 
be split radially. The cleft, which closes after the 
abatement of the frost, is now rapidly overgrown ; 
the dead bark is thrown off at once and the over- 
growth edges unite. In this, the union takes place 
after the manner of frost ridges, i. e., the edges rise 
up like ridges above the normal plane of the annual 
ring, while the broad wounds which are closed very 
slowly show the axial cylinder to be flattened at the 
frozen place. 

In both cases, however, the overgrowth edges are 
distinguished by the fact that they arise under the high 
pressure of the dead bark and, on this account, are 
smallest at the outermost ends and pointed like wedges. 
This ■wedge-like groivth of the overgrowth edges, 
ivhich spread out over the dead surface, is a character- 
istic of blight in contrast to canker. The overgrowth 
edges of canker increase in thickness towards the place 
of injury and, like rolls, sink down into the open split 
which forms the beginning of the canker. 

It may easily be seen, that the tissues of the over- 
growth edges differ according to the pressure condi- 
tions, under which they arise. This has been discussed 
more in detail under canker. 

In Fig. 147, the dark place B corresponds to the frost plate p in Fig. 
145; t is 3. piece of dead bark, the healthy part of which (R), recognizable 
by its white, glistening, hard bast bundles (hb), is separated from the dead 
tissue by a diagonal cork zone, adjoining the normal cork covering (/v) at 



V 



Fig-. 146. Young peai- 
trunk with different 
liinds of blight spots. 



6ii 



B. The annual ring, produced after the frost, is marked /. If this is fol- 
lowed back to the place of injury^ it is seen to diminish suddenly to a point 
and to be entirely absent under the dried, dead place in the bark {f, t). 
Only the next annual ring would be able to push between these. The 
structure of these pointed overgrowth edges resembles much more the 
normal wood because of the very scantily formed parenchyma wood and 
the rapidly appearing thick-walled wood cells together with the ducts, than 
does the lip-like wood parenchyma overgrowth edges of the canker (cf. 
"Open canker"). 

In the adjoining Fig. 147 
we see, above the pith bridge 
(m), the normal annual rings, 
interrupted by darker, sickel- 
shaped zones (/>-), which here 
appear gray. These zones con- 
sist at times of thinner walled, 
ductless, shortened parenchyma 
cells, and at times of wood 
parenchyma, richer in starch. 
In luxuriantly growing varie- 
ties the radii of the medullary 
rays, which here are straight, 
appear somewhat bent and dis- 
place the longitudinally elon- 
gated wood cells and ducts 
from a diagonal to a horizontal 
direction. 

It was stated above that the 
frost plates should be consid- 
ered as narrowly limited scald 
injuries of relatively small ex- 
tent in all directions, which 
could, however, be found dis- 
playing all transitions up to 
large, blasted surfaces cover- 
ing the whole side of the tree. 
Besides occurring in pears, 
such frost plates may also be 

found in the red beech. On branches of a beech thickly covered by such 
plates, the browning of the contents of individual cells, scattered through 
the pith, could be proved to be the final radiation of the frost action in its 
furthest extension into the healthy tissue. These cells undoubtedly have a 
different content from the other pith cells, which have remained colorless 
and, in cell contents, probably approach most nearly those of the medullary 
crown, which likewise easily become brov;n. 




Fig-. 147. Cross-section through a pear stem 
at a blight spot, produced by frost. 



6l2 

The browning does not extend into the surrounding tissue, as in wound 
rot, for the cells already existant, as well as those formed later in the imme- 
diate proximity of the tissue browned by frost, remain clear-walled and 
healthy. The browned medullary cells contain as much starch as do those 
not attacked, so that the brown color can not arise from a change in the 
starch but from some other substance. The pith does not suffer in every 
case. Often the wood in 2 to 3 year old branches is so browned that a 
yellow, gum-like filling of the ducts extends up to the medullary crown and 
the medullary rays also appear brown almost to the centre; the pith itself, 
however, having no diseased discoloration whatever. Such differences 
take place in different internodes of the same branch. Nevertheless, the 
rule holds that the initial stages of browning are found, on an average, in 
scattered cells of the pith, especially those of the pith crown ; that, at first, 
only the contents and then later the walls themselves become discolored and 
that this discoloration of the contents seems to consist of a browning and 
thickening of the cell fluid. The gum-like soHd masses can break in sec- 
tioning into angular pieces. I believe the filling of the ducts must be traced 
back in part to the hardening of the fluid contents already existing, in this 
way easily explaining the often drop-like formation of the filling substance. 

With increasing cold the browning of the pith, as a rule, follows that 
of the medullary rays and bast parenchyma groups in the bark. In branches 
of the red beech frost action, limited to individual vascular bundles, can 
often be recognized; the discoloration is restricted to the inner half of two 
main medullary rays, attacking first the part of the bundle which belongs 
to the medullary crown and often ending suddenly with the boundary of an 
annual ring. 

At times the wall of the duct may be found unstained or only discol- 
ored on one side, while the contents seem completely discolored. It was 
mentioned above that the secondary membrane can also participate in the 
filling of the ducts and wood cells. At first this swells up and at times, in 
fact, completely fills the lumen of the wood cell, or of the narrow duct, 
which then seems colorless and refracts the light uniformly. Besides this, 
cells and ducts are found which have turned a deep brown ; their cell con- 
tents often lie in the form of drops or rings against the wall, but sharply 
separated from it. In other cases there is no separation between the cell 
contents and the cell wall and here the participation of the wall in the 
change Is certain. It also may happen that only an inner layer of the cell 
wall turns brown, swells up and finally becomes rigid. This swollen layer 
then has not space enough on the inner side of the cell, or of the duct, and 
folds inward so that a colorless cavity is found between the brown wall 
layer, which has been pushed inward, and the outermost, unchanged portion. 

In the browning of the cambium, which usually occurs only on one side, 
the contents are only sHghtly browned and the cell wall does not discolor at 
all until later. The spring wood, directly adjoining the autumn wood, seems 
to be most sensitive. It is evident in the bark, that the parenchymatous 



6i3 

cells, extending in the form of an arch from bark ray to bark ray, and 
already elongated; sufifer less than the inner, small celled tissue which 
bounds them. 

The observations, here mentioned, illustrate frequent, isolated cases 
but not phenomena of universal occurrence. Finally, a case in the sweet 
cherry should be mentioned as especially noteworthy. The pith of a one 
year old branch seemed split at one side up to and beyond the centre and 
the cells of the periphery of the pith grew out like filaments into the result- 
ing cavity, similar to the woolly stripes of the apple core. No gummosis 
was present. The case was obser\'ed in the so-called "frost-wrinkles." It 
is interesting because it shows that the activity of growth in the pith, which 
in general occurs only in soft wood trees (Tilia), can be reawakened here. 

In the above mentioned phenomena of scald is also found, as a rule, 
an increase of the gum centres in the Amygdalaceae and of the resin centres 
in conifers, with an increase of the parenchyma masses (Fig. 147 pz) be- 
tween the normal parts of the annual ring, just as in canker. In canker, 
it can also be proved that the breaking up of the bark due to a weakening 
of the mechanical ring corresponds to the breaking up of the wood by 
parenchyma wood in the same radius. The hard bast bundles are absent 
from the bark of the overgrowth edges just as are the real, thick- walled 
wood cells in the wood of these edges. 

Aggregations of Parenchyma Wood. 

In canker excrescences, we have seen how tender and perishable the 
wood ring becomes as soon as it passes over into the overgrowth edges of 
a narrow cleft at the time of the greatest growth activity in the spring. 
Because of the rapidity of the production of such large tissue masses, the 
wood ring does not have time to mature prosenchymatous elements but at 
first is formed of parenchymatous, thin- walled elements which, to be sure, 
have some advantages as a storage tissue for reserve substances, but show 
very sHght power of resistance to parasitic and atmospheric influences. It 
is therefore easily understandable that even in healthy trees the appearance 
of parenchyma, instead of prosenchyma wood, deserves especial attention 
from a pathological standpoint. Such cases may be found everywhere. 

The aggregations of parenchyma wood can occur in the trunk in the 
form of scattered nests, or in ring-like bands, differing in length and width. 
They have been variously named. We find an enumeration of such cases 
in de Bary^ , who sees in them an hypertrophy of the medullary rays. 
Rossmassler calls them "Repetitions of the pith;" Nordlinger, "pith spots," 
while Th. Hartig- speaks of "cell passages." The most mature form is 
found in the so-called "moon rings." These are brown, or white, bands of 
parenchyma wood, usually extending in a ring partially or entirely around 
the trunk. This parenchyma w^ood appears at times to be decayed like 

1 De Bary, Verg-leichende Anatomie der Vegetationsorg-ans 1877, p, 567. 

2 Hartig, Th., Vollstandige Naturgeschichte der forstlichen Kulturpflanzen. 
1852, p. 211. 



6i4 

tinder. These decayed tissue masses not infrequently give a cellulose 
reaction. Such tissue is often found traversed by mycelium. Th. Hartig 
describes the fungus as Nyctomyces candidus and N. titilis. Rob. Hartig 
ascribes the mycelium observed in oaks to Stereum hirsutum Willd^ In 
other tree genera, other fungi are found which destroy the wood and which 
are treated more thoroughly in the second volume, p. 385 ff-. 

In cross-sections of the wood structures termed "pith spots" appear as 
isolated, sharply bounded, somewhat crescent-like, browned, decayed spots, 
which, like passages, may be followed downward to different distances in 
the trunk. We owe a thorough study of these to Kienitz-Gerloff^, who 
observed that in willows, mountain ashes and birches it is caused by the 
feeding of an insect larva. According to a review by Karsch* Tipula 
suspecta, Rtzb. is concerned here. This larva feeds "on the cells of the 
cambium and the youngest wood at the time of the formation of the annual 
ring." The passages, made by it, are closed as follows; — "the cells, break- 
ing through the edges of the wound, grow quickly and divide with delicate 
cross-walls. At the same time, a complete closing of the cambial ring takes 
place and, from now on, the normal wood and normal bark are formed over 
the wound surface, while the cavity, perfectly independent of the new 
cambium, is closed by the increase of cells'^. These injuries, due to filamen- 
tous diptera larvae, which bore their v. ay into the cambial zone, especially 
at the base of the trunk and the root neck, sometimes even higher up in the 
shaft, and in water sprouts in May and June, are primarily considered as 
producers of pith spots or "brown chains" only in the varieties of trees 
named. Kienitz remarks that similar structures in other trees, especially 
conifers, do not arise from the diptera larvae above mentioned. 

In regard to the pith spots of the birch, v. Tubeuf' confirms the inves- 
tigations of Kienitz and mentions thereby that G. Kraus explains these cell 
aggregations as normal structures. De Bary, as was said above, speaks of 
hypertrophies of the medullary rays and, at the first glance, one also gets 
the impression that the pith spots are caused by a widening of the medullary 
rays. These are seen actually to become broader before they enter the 
aggregations of parenchyma wood and their cells take on the polyhedric, 
thick-walled, greatly pitted appearance of the cells of the pith spot which 
are filled at times with starch and brown tannic substances. In fact, it is 
often found that the medullary rays, when entering the pith, are broadened 
and unite laterally. But, supported by my "barking experiments," I con- 
sider the newly formed, filling tissue to be a product of some cell increase 
which can take place not only in the medullary rays but in all the tissue 



1 Hartig, Rob., Zersetzung-serscheinungen des Holzes, p. 129. 
~ Paging in the German original. 

3 Kienitz, M., Die Entstehung der Markflecke. Bet. Centralbl. 1883, Vol. XIV, 
p. 21 ff. Here also bibliography. 

4 Bot. Jahresbericht. Jahrg. XI, Part 2, p. 518. 

5 Bot. Jahresber. 1883, Vol. I, p. 182. 

e V. Tubeuf, Die Zellgange der Birke und anderer Laubholzer. Frostl. naturwiss. 
Zeitschr. 1897, p. 314. 



6i5 

forms composing the annual ring. The growth of the medullary, or the 
bark rays, only exceeds that of other tissues in all processes of zvound heal- 
ing; it thereby becomes predominate. 

Also if, in the above mentioned "moon rings," the boundaries between 
the already destroyed parenchyma wood of the annular bands and the 
healthy tissue are investigated, not infrequently a striking widening of the 
medullary rays is found, especially in oaks. 

In conifers, especially pines, a still more extreme form of disturbance 
may be found, the so-called "ring-barking." At times, when the trunk is 
split, a complete cylinder, beginning at the healthy central portion of the 
trunk, separates from the apparently ecjually healthy peripheral wood, as 
from a shell. This takes place because the tissue is destroyed in one, and 
indeed only one annual ring, becomes rotten and traversed by mycelium. 

This form of ring barking is distinguished by its sound, healthy core 
from the one studied by Robert Hartig^ in the pine, in which a wound 
parasite, Trametes Pini (Brot.) Fr. causes the destruction of the core but 
does not extend into the healthy sap-wood. Hartig describes the rapid 
advance of the mycelium in the medullary rays and, after having discussed 
the destruction of the wood caused by the mycelium, the dissolution of the 
incrusting substances and the retention of the cellulose in the wood fibres, 
says that, "as the result of the collapse of the wood which is connected with 
this decay and loss of water, not only are radially extending cracks formed 
but often the outermost annual layers are loosened as a mantel from a 
thicker or thinner core. Thus annular clefts are produced which can have 
led to the name of "ring barking." We are here, therefore, concerned with 
a form of very extensive red rot, or heart rot. According to v. Tubeuf, 
the fungus appears also in spruces and has been observed in larches and 
white firs and, in America, in the Douglas fir. Emphasis should be laid 
on the fact that this mycelium spreads "very easily in one certain annual 
zone- and the diseased, white tissue aggregations, which now consist only 
of cellulose, may be found abundantly in the spring wood"^. This seems to 
me to indicate that the fungus finds greater resistance in the adjacent annual 
rings, i. e., the annual ring already attacked must necessarily have been 
more porously constructed. Accordingly, bands of parenchyma wood 
might contribute especially not only to infection of branch wounds by 
Trametes and other wood destroyers, but also to their distribution in the 

trunk. 

False Annual Rings. 

Double Rings, Etc. 
Its is a well known fact* that the size and constitution of ever}^ annual 



1 Hartig-, R., Wichtige Krankheiten der Waldbaume. Berlin 1874, p. 55. 

2 V. Tubeuf, Pflanzenkrankheiten diirch kryptogame Parasiten verursacht. 
Berlin 1895, p. 471. 

8 Hartig, R., Lehrbuch der Pflanzenkrankheiten. Berlin 1900, p. 172. 
* Kiister, E., Pathologische Pflanzenanatomie. Jena 1903. p. 25, etc. Here also 
pertinent bibliography. 



6i6 

ring in woody plants depends upon the amount and kind of leaf activity. 
This has been thoroughly treated in forestry literature. Every considerable 
interruption in the activity of the leaf apparatus makes itself felt in the 
wood and can lead to the omission of wood formation in one side of the 
tree, or at the base of the trunk and in the root. If the cambium, which had 
been active in the spring, is incited to renewed increase in the same year 
after a period of inactivity, it begins the formation of a new spring wood 
which passes over into autumn wood, sometimes more slowly, sometimes 
more quickly. In this way a new, normal, annual ring is produced. In 
such cases are found semi-circular double rings, or others encircling the 
whole girth of the trunk. 

We owe exact studies on this subject to Kny^, who determined espe- 
cially clearly in Tilia parvifoUa that, after the sprouting of the buds on 
shoots which had been entirely defoliated by caterpillars, a second annual 
ring was formed. The boundary between the newly formed spring wood 
and the wood ring produced before defoliation is sharp. In Ratzeburg's- 
study we find repeated examples of the dependence of the formation of the 
annual ring on the time of defoliation. Since different insects can cause 
complete defoliation, at different times of the year, a weakening of the 
growth of wood is found sometim.es in the same year, but, at other times, 
not until the following year (when the deposition of reserve substances is 
scanty). 

In 1886, I was able to add the action of frost to the causes which can 
bring about the formation of false annual rings. In 1895 R. Hartig'' pub- 
lished a treatise in which he described frost rings m the oak and fir and 
considered also a different mechanical effect, viz., a drooping of the shoots 
due to a loss of turgidity. This bending of the shoots became permanent 
and could be found the following year. The drooping can also occur as a 
result of the destruction of the pith parenchyma. In the last edition of 
Hartig's text book*, frost rings from the wood of a pine and of a spruce 
are illustrated with the remark "in older parts of the trunk of the pine it 
was found that a so-called double ring was produced in each year of late 
frosts. I later confirmed the fact also in spruces and other conifers, that 
a late frost not only injuries the youngest shoots but even produces the 
'double rings' formed in parts of the trunk v^diich were ten years old." 

O. G. Petersen'^ describes and illustrates a similar disturbance in the 
structure of the annual ring of beech trees which had suffered severely from 
frost on the 17th to i8th of May, 1901, in Holland. Nordlinger*' had 



1 Kny, L., tJber die Verdoppeliuig des Jahresringes. Sep. Verhandl. d. Bot. Ver. 
d. Prov. Brandenburg- 1879. Here also discussion of earlier theories. 

2 Ratzeburg-, Waldverderbnis, I, p. 160, 2.^4; II, p. 154, 190. 

8 Hartig, R., Doppelringe als Folge von Spatfrost. Forstl. naturw. Zeitschrift 
1895, p. 1-8. 

4 Lehrbuch der Pflanzenkrankheiten. Berlin, Springer 1900, p. 220, 221. 

■'■' Petersen, O. G., Natterfrostens virkning- paa Bog-ens ved. Sep. Det forstl ige 
Forsogsvaesen, I. 1904. 

c Nordlinger, Die fetten und die mageren Jahre der Baume. Kritische Blatter 
E. Forst- und Jadgw'issenschaft, 1865, Vol. 47, Part 2. 



6i7 

already observed in the normal wood formation a ring-like break in the 
form of a line of reddish tissue. Corresponding reports and observations 
may be found elsewhere which, however, do not contain any new points of 
view. Studies on canker phenomena increased our imderstanding of the 
disturbances in the formation of annual rings. I have proved in the apple 
canker that an annual ring, which is simple and normal on the healthy side 
of the branch, may be subdivided on the canker side into several ring zones. 
My recent studies on the oak have shown how such a breaking up of the 
tissue may take place. 
Experimental Production of Parenchyma Wood by Frost Action. 

The cases of the production of parenchymatous wood tissue instead of 
normal parenchyma, described in the preceding chapter as "pith spots," 
"parenchyma wood bands," "ring shells," etc., arise from a variety of causes 
which, however, as a whole, agree, in that the cambium in different parts of, 
or to the whole extent of the annual ring, is more or less freed from the 
pressure of the bark girdle binding it. It may be concluded from subse- 
quent observations that frost, and especially spring frosts, furnish one of 
the most essential and frequent causes of such a loosening of the bark girdle. 

In 1904, in May, a frost had so greatly injured the younger oak shoots 
near the edges of different forest plantations, where these bordered on open 
meadows, that a number of branch tips were completely frozen while only 
the leaves of others had blackened and dried; later they continued their 
growth at the tips. When these shoots, within a few weeks, had again 
formed new leaves, they were cut for investigation. They showed great 
differences in structure, among others that illustrated in Fig. 148. 

We recognize an irregularly pentagonal medullary body (ni) sur- 
rounded by slender wood rings (h) more strongly developed on one side. 
This wood ring, however, on the outside, does not adjoin a regular cambial 
zone, as is the case in the normal branch, but passes over suddenly into a 
porous, wide-celled parenchyma wood (ph) which becomes thicker walled 
toward the bark and only rarely leaves recognizable a cambial boundan,' 
zone between itself and the bark. That this girdle (ph) formed of porous 
tissue still belongs to the wood ring and has arisen from it, is proved by the 
short-celled, vascular elements (g') scattered in the zone of thin-walled 
cells which, in the structure of their thickening layers, seem similar to 
those of the ducts in the normal, first formed wood ring, or resemble them. 
This presence of short ducts, or duct cells, and the condensing of the whole 
zone of thin-walled cells at its periphery by the occurrence of thick-walled 
elements, resembling the true wood cells, shows, therefore, that this branch, 
injured by frost, had re-adapted itself to the normal formation of the wood 
ring a short time after the cessation of the frost action and the formation 
of the parenchyma wood. 

If this branch had been allowed to continue growth until frost, we 
would then have had a second false annual ring, as has been observed by 
earlier investigators and was discussed in the preceding chapter. 



6i8 

The bast ring (h) has been less affected ; only the contents of the young 
bast cells are usually found to be brown, corresponding to the filling of the 




Fig-. 148. A healed internal frost wound on a young oak branch, caused by injury 

from a May frost. 

( canibial zone, z zigzag line with swollen cell walls, .r vessels in the normal wood. 
Explanation of the other letters to be found in the text. 



different ducts of the wood ring wath a reddish yellow, gum-like substance. 
The bark parenchyma contains single, brown groups. No special phenomena 



6i9 

of discoloration are visible in the coUcnchymatous outer layer of the bark 
but may be found in the pith crown, which appears to be entirely brown. 
This browning decreases with the distance towards the healthier base of 
the branch at which the sections were made. At the base of the branch 
we find only scattered cells, with yellow, swollen contents. 

A difference in direction of the holes thus produced becomes noticeable 
in the abundantly recurring cracks. Within the pith disc may be found 
the greatest radial extension of the holes which is seen to be connected with 
a peculiar, radiating formation of the pith. This is found to be distended 
into a pentagon, produced by the passing of the vascular bundles, com- 
posing the wood ring, out from the wood ring. As indicated above, the 
cau^e of this extension of different bundles lies in the fact that, in each of 
the five corners of the pith, the vasctdar systems, destined for the five next 
higher leaves, are about to make their way outward through the bark into 
the leaves. The pith body for the leaf lying next above the part of the 
branch here illustrated, is naturally furthest distended and is adapting itself 
to passing over, as a pith connection (mb), into the next bud. The bundles 
of the two higher leaves, lying only one or two internodes above the place 
of the cross-section, still lie within the complete wood ring, but even they 
have already formed noticeable distentions of the axial cylinder (at the right 
in the figure). The bundles for the 4th and 5th leaves, following the spiral 
of the leaf insertion, still lie entirely within the wood ring and indicate 
their lateral appearance only by a slight outward convexity (at the left side 
of the figure). Between them the pith body is continued only in the form 
of a broadened medullary ray and has not widened into an actual pith 
connection. 

The holes (l), produced by the rupturing of the tissue, correspond in 
size to the amount of distention of the pith. The larger these are, and the 
nearer they stand to the buds belonging to them; the stronger is the radial 
splitting. Differing from those in the pith, we find the holes (/') in the 
bark extending tangentially. The}^ are produced, in part, by the throwing 
off of the peripheral collenchyma of the parenchyma, rich in chlorophyll, in 
part, however, by the rupturing of individual parenchyma cells. It should 
be noticed, that the formation of holes in the bark, as also the formation of 
thin-walled tissue (ph-lg), is much greater on the side of the branch where 
the bundle has separated most widely from the main vascular system than 
on the opposite side. Moreover, this also explains the fact that, in the 
investigation of branches injured by frost, as a rule, one side is found more 
greatly affected than the other. The natural conclusion, that the action of 
the frost has been greater on one side is usually erroneous. For, if a num- 
ber of successive internodes are examined by series of sections, the investi- 
gator will be convinced that sometimes one side of the same branch shows 
a greater injur}' from frost, sometimes the other, according to the position 
of the bud, near which the section was made. The closer to the bud, the 
stronger the action of the frost in the branch. 



620 

After numerous vain attempts, the abo\e described disturbances in 
tissue, and processes of healing, could at last, in the spring of 1905, be 
produced artificially. In April potted specimens of 4 to 5 year old oaks 
were brought into a greenhouse for forcing. The tender young shoots 
were exposed in May for one night to a temperature of 4 degrees C. below 
zero in a freezing cylinder. The plants were then left out of doors and 
investigated the middle of June. Here, exactly as in the observations made 
the previous year on naturally frozen oaks, the branches, injured by frost, 
showed very different forms of disturbance. Among them were some 
resembling typically the natural injuries described above; only the processes 
of healing, which here begin clearly at the medullary rays, were much less 
extensive, which may be traced to the fact that potted specimens always 
develop more weakly and slowly than forest trees growing in open ground. 
The observation was also made, that the clefts in the tissue seemed to be 
less extensive, the older and stronger the branch was at the time of the 
frost action. I conclude from this that injury from frost only leads to 
the formation of parenchyma wood within an annual ring when it affects 
very young, tender shoots at the time of the greatest growth in length. 
Besides this, favorable, warm weather must follow the frosty nights so that 
cell increase can continue at its former rate. The building material, in the 
form of mobilized reserve substances, is present in the branch, injured by 
frost, in the same amounts as before the action of the frost, but the newly 
produced cell elements develop differently because the conditions of tension 
in the branch and the resulting pressure on the cambium have become dif- 
ferent, due to the breaking up caused by frost. 

The Theory of the Mechanical Action of Frost. 

The phenomena, which came to light in the above described natural 
and artificial frost injuries to young branches, however they may vary, can 
be traced to simple mechanical processes. In this we still refer to the above 
illustration of the oak branch in which we see that the pentagonal wood 
ring, surrounding the medullary disc, passes over suddenly into a light zone 
of delicate tissue (Ig) and this gradually forms, toward the perihpery, 
tougher elements, which have the character of normal wood (h). 

The illustrations 2 to 6 in Fig. 149 serve to orient the place of origin of 
the thin-walled tissue. These show enlarged portions, drawn cell for cell 
from the right side of the above figure (Fig. 148) at the region of the sec- 
tion, lying between Ig and b. In all the drawings, the upper angle is the one 
toward the pith, the under angle the one toward the bark which, in fact 
(Fig. 149 2, 4, 6) even shows bark elements. The uppermost cell groups, 
in part designated by h, form the boundary of the wood ring which was 
present before the action of the frost. These pass over directly into the 
thin-walled tissue {Ig) of the thin-walled stripe (Fig. 149 2, j). In this, 
the medullary rays, which in normal wood are only one to two cells broad 
(Fig. 149, ^ m s) have become enlarged and irregularly many-celled. They 



621 




Fig-. 149. Cell groups from the transitional region between the normal wood ring 
and the stripe of thin-walled, loose parenchyma wood, produced by frost. Taken 
from the zone Ig-b in Fig. 148. z, in Fig-. 2 and 5, indicates the zigzag lines with 

their swollen cell walls. 



622 

contract to their former breadth only wliere the porous tissue passes over 
into the secondary wood (Fig. iz|9 2, 5, h!) with regular ducts {g'). Then 
a normal cambial zone is formed again (Fig. 149 2 c^ which, at the time 
when the medullary rays were broadened excessively, had become irrecog- 
nizable, since cell division took place absolutely irregularly in different 
regions of the ring of thin-walled tissue. As soon as the formation of the 
regular cambial zone begins again, the h^ose bark tissue also differentiates 
itself in such a way that juvenile bast groups (Fig. 149, 7 h and 6 b b') 
again becomes recognizable. 

The fact, that no dead tissue of any kind is present between the wood, 
matured before the action of the frost (h), and the looser, thin-walled 
tissue (Ig), proves that the young wood, the sap wood ring, has passed over 
directly into the parenchyma wood of the ring of thin-walled tissue. Never- 
theless, this parenchyma has retained its connection with the wood body. 
On this account, it is not surprising that, after the cessation of the causes 
which had brought about this parenchymatous formation of wood, the tissue 
gradually re-assumes the normal wood character and adapts itself to the 
formation of a secondary wood ring (Fig. 149 2 and j h'). In fact, indi- 
vidual elements of the sap wood, the thickening of which had advanced 
somewhat further at the time when the formation of parenchyma wood 
began, had continued the thickening of their walls. On this account, we 
find isolated tracheal elements (Fig. 149 4, tr) in the centre of tlie paren- 
chyma wood. 

The zone of thin-walled, porous tissue (///) in the cross-sertion of the 
oak branch (Fig. 148) is, therefore, only a modified wood ring which has 
passed over into an excessive new cell formation. Since such a cell increase 
can arise only from elements which still possess their cambial nature, it 
must necessarily be concluded that the very youngest cambial zone elements, 
i. e., the sap wood, have produced this parenchyma wood. As a matter of 
course the real anatomical cambium, together with the young bark, has par- 
ticipated in this cell increase and, in this way, produced the abundant tissue 
in which it is not possible to distinguish where the transition from wood to 
bark takes place. 

We now ask what may be the cause of the formation of this profuse 
tissue zone? The answer can only be found in the removal or weakening 
of the constricting, compressing influence, exercised by the bark girdle, as 
a whole, on the youngest tissue, i. c, the cambial region. 

This cause is indicated by the holes in the bark tissue (Fig. 148 /', at 
the right). Such tangential holes in the healthy tissue are produced by the 
upraising of the tissue lying above the hole from that lying beneath it. It 
can only be raised, however, if it has not enough room on this underlying 
parenchyma which is caused by a greater tangential distention. Conse- 
quently, a stronger tangential strain has occurred in these outermost tissue 
layers than in the adjacent inner layers of the bark. 



623 

Caspary's measurements in freezing should be recalled here. The 
peripheral layers contract earlier and more strongly than do the central 
layers. This contraction with cold is stronger tangentially than radially 
and greater in the delicate parenchyma than in the prosenchyma wood. Con- 
sequently, with the action of frost, there must take place everywhere within 
a woody axis a preponderance of tangential strain over radial contraction 
and, under certain circumstances, this must increase to a radial splitting of 
the tissue.. 

If the wood ring is thought of, first of all, as isolated, this preponder- 
ating tangential contraction in places of least resistance would necessaril}' 
lead to such clefts as would correspond to the gaping frost cracks in old 
trunks. Therefore, inner clefts must be produced from purely mechanical 
causes and, in fact, in the medullary rays and medullar}^ transverse connec- 
tions. Such are actually shown in the illustration of the oak branch, injured 
by natural frost (Fig. 148). 

If we now consider the primary wood ring in its relation to the adjoin- 
ing bark girdle, we must refer again to the fact that the bark girdle, of 
which the peripheral cells are larger tangentially than radially, contracts 
more strongly tangentially and, therefore, is strongly torn in this direction 
during the action of frost. If the frost grows less, this cracking may cease, 
indeed, but its efifects remain, for the tissue which may thus be stretched, 
is not absolutely elastic and does not contract to its former volume. In 
this way each frost action leaves behind an excessive lengthening of the 
peripheral tissue layers in proportion to the adjacent layers which lie more 
toward the inside. The bark body, as a whole, therefore, is longer and 
either does not have room enough on the wood cylinder so that in places 
it is raised up from it, or it at least curves outward, i. e.. it decreases its 
constricting influence on the cambial elements of the wood cylinder. 

The cambial zone responds to this with a formation of parenchyma 
wood, as may be seen in every wound in which the bark is raised. If the 
bark girdle closes together again into a connected layer the cambial cylinder 
of the branch, by growth in thickness, must again resist the constricting 
effect of the bark and, on this account, again forms normal wood elements. 

Thus the formation of the parenchyma wood bands in young branches 
comes under the same law of unequal contraction which, in old trunks, 
leads to the production of gaping frost clefts. 

The Rupture of the Cuticle. 

The experiments on potted specimens of forced oaks, mentioned in the 
previous section, proved the fact, not known until then, that, on superficially 
browned, or still green leaves, i. e., those outwardly but little affected, a 
repeatedly interrupted black, very fine line is formed on the under side, 
which gives the impression of very fine particles of soot which had settled 
on it in places. With a higher magnification, it is seen that this line consists 
of small raised places in the outermost cuticular layer which- because of its 



624 

granular condition, retains the air, and therefore appears black. The small 
granular papillae still remained when the leaf was destroyed by sulfuric 
acid ; in which treatment the leaf curled up like a worm and the epidermis 
of the upper side puffed out in places. 

This result agrees with discoveries which had been observed earlier in 
beech trees after natural late frosts, and which we could prove also on oaks 
in the open. In the production of such scarcely perceptible rupturing of 
the cuticle, some special conditions must also have co-operated which were 
present accidentally in the experiments but do not seem to be always effec- 
tive in other experiments or in nature, for, soon after late frost, such injured 
oak leaves could be found in some localities but not in others. Probably a 
definite condition of turgor in the leaf is connected with it and this will be 
dependent again on the constitution of the cell contents at any given time. 

A conception of the fine differences, which are decisive in frost inju- 
ries, is obtained from the obser\'ation that dead particles of tissue, injured 
by frost, may be found at times in the centre of the mesophyll of the leaf, 
which apparently is but little, if any injured. The fact that, in experi- 
ments, these cuticular breaks appear only on the imder sides of the leaves 
may be traced perhaps to a constitution different from that of the upper 
cuticular covering, for it is found that in the action of sulfuric acid, the 
upper covering turned a bright lemon yellow, which color shade was 
scarcely perceptible in the cuticle of the under side. 

I would like to lay especial value upon the discovery that, under certain 
circumstances, a rupturing of the cuticular glaze can be produced by light 
frost. In other breaks in the cuticle (in pomes) fungus spores were found 
lying in the line of the break and it may, therefore, not be out of place to 
assume that, in these protected places, such fungus spores have the best 
opportunity to germinate and to sink their germinating tubes into the organs. 
In this way might, therefore, he explained the attacks upon apparently per- 
fectly healthy leaves and fruit by fungus infection after a light spring frost. 
Voglino's^ reports might be referred to here. In 1903, after some frost in 
April, he found that the fungous parasites had an especially large distribu- 
tion in plants injured by frost. 

Thus is explained also the phenomenon of the so-called rust etchings 
in connected rings and irregular surfaces on our fruit. They are cork 
formations w^hich have set in, in the cuticular tears, as a result of the 
processes of healing, while the normal cork etchings on the fruit usually 
begin at the stomata, or rather, the lenticels. 

Protective Measures Against Frost. 

(a) Snow Covering. 

The process, universally used for protecting plants against frost, con- 
sists in surrounding them with substances which are poor conductors of 



1 Voglino, P., L'azione del freddo suUe piante coltivate, specialmente in rela- 
zione col parassitismo del funghi. Atti accad. di Torino XLVI. 



625 

heat. Grapevines, roses, etc., are covered with earth or leaves, or the 
trunks are wrapped in moss, straw and the like. All these means are good 
but in cold winters, with a moderate snowfall, one should not delay throw- 
ing the snow from the streets on to the covered plants. It is well known 
that wrapped trunks of roses, for example, often freeze; this is explained 
by investigating the temperature under the covering material with a ther- 
mometer. It is found to deviate but little from the temperature of the outer 
air. On the other hand, if the soil under the snow covering, possibly 15 cm. 
deep, is investigated, it is found to be considerably warmer. Goppert's 
investigations^ are the best on this subject. In February, 1870, the tempera- 
ture was very low. The thermometer fell on the 4th to 12.6 degrees below 
zero, on an average, and yet in this, the temperature was only 3 degrees 
below zero under the snow covering, 10 cm. deep. The temperature of 
the air 

on Feb. 5 was 14 1 degrees below zero, the temperature under the snow 4.6 degrees 

below zero, 
on Feb. 6 was 17.6 degrees below zero, the temperature under the snow, 5 degrees 

below zero, 
on Feb. 7 was 16.7 degrees below zero, the temperature under the snow, 5.5 degrees 

below zero, 
on Feb. 8 was 16.7 degrees below zero, the temperature under the snow, 6.5 degrees 

below zero, 
on Feb. 9 was 15,4 degrees below zero, the temperature under the snow, 6 degrees 

below zero, 
on Feb. 10 was 14.9 deg'rees below zero, the temperature under the snow, 6 degrees 

below zero, 
on Feb. 11 was 15.8 degrees below zero, the temperature under the snow, 5 degrees 

below zero, 
on Feb. 13 was 5.7 degrees below zero, the temperature under the snow, 2 degrees 

below zero, 
on Feb. 16 was 2.8 degrees below zero, the temperature under the snow, 1.5 de^ees 

below zero. 

The soil under the snow covering was frozen 36 cm. deep, but its tempera- 
ture, even on the cold 5th of February, at a depth of 5 cm., was only one 
degree below zero. 

It would scarcely be possible to find more eloquent proof of the useful- 
ness of a snow^ covering. This explains the possibility of polar vegetation. 
The greatest degrees of cold in the polar zone as yet observed (40 to 47 
degrees below^ zero) afifect only the trunks of the trees which project above 
the snow, but not the roots. Perennial, herbaceous plants are just as little 
affected. These stand in a soil with a temperature under the snow cover- 
ing of only a few degrees below zero. The snow covering, to be sure, does 
not arrest freezing but does prevent loss of warmth through radiation, the 
penetration of greater degrees of cold and a rapid change in temperature. 
But, even with us, the existence of many plants is more often connected 
with snow covering than we think. The freezing of seed would occur 
much more frequently when a long damp and moist autumn favors plant 
development, if the snow covering were not deposited on them, which keeps 
off radiation and the great fluctuations in temperature, so frequent in our 
latitudes. We see often enough how easily insufficiently protected, or fully 



1 Bot. Zeit. 1871, No. 4, p. 54. 



626 

exposed parts of plants freeze, if struck by sudden strong sunshine. The 
cell contents, suddenly struck in a condition of rigidity, the result of cold, 
are found poor in water content and drawn back from the cell wall, and do 
not have time to distend again, by absorbing water, into their normal rela- 
tion with the cell wall, and, thereby, the surrounding tissues. In this way, 
the disorganization of the cell begins. These are the processes which occur 
with spring frost and are especially advantageous for garden plants. 

(b) The Use of Water. 

Especially herbaceous plants which are suddenly exposed to frost are 
benefited if the hard frozen parts of the plants are watered with right cold 
water and then shaded. The water on the plants freezes to an ice crust, 
thus raising slowly the temperature of the plant itself to zero, and it can 
gradually be warmed further above this temperature, after the thawing of 
the crust. 

On the same principle of gradual warming rests the plunging of frozen 
potatoes and roots into a vat full of cold water and the piling of frozen 
cabbage heads in heaps which are then covered with straw mats. 

In spring and autumn, when the air temperature does not fall' to zero 
but the plants, because of their radiation of heat under a bright sky, cool 
down below zero, become covered with frost and freeze, they may be pro- 
tected by substances arresting radiation. Covers and mats are spread over 
the plants, also very thin cloths are effective here and, if no other covering 
material is at hand, a thin layer of brush is very useful; even perpendicular 
walls have proved excellent protection against frost. They are effective, 
on the one hand, by keeping ofiF the wind and, on the other, by decreasing 
radiation from the plants. In trees, trained against stone or wooden walls, 
in addition to the very considerable decrease in radiation of the trees on the 
side next the wall, the wall itself gradually gives up its stored heat to the 
benefit of the trees. 

A less effective, but not entirely rejectable, protection against frost is 
recommended by older authors and is practical in gardens in spring. The 
trunks of trees are wound with straw rope one end of which dips into water. 
Straw and tow ropes are suspended in all directions over beds of blooming 
spring plants some distance above the surface of the soil, their ends being 
held fast by stones in a vessel filled w^ith water. 

To understand the favorable effect of this process, one should remem- 
ber the great latent warmth in the water. If the water in the saturated 
straw ropes freezes, heat is set free which is advantageous, since it prevents 
the penetration of the cold to the underlying parts of the plants. Thus 
plants, near larger bodies of water, freeze less easily. One measure used 
with good results for potted plants, at a time when night frost may be 
feared, consists in a decreased watering, whereby the tissue of the plant 



627 

contains less water when it is exposed to the frost. A more abundant 
evaporation removes more heat from the plant and, therefore, heavily 
watered plants will cool down more than those which are less turgid. 

(c) Effect of Wind. 

Winds can also act favorably inasmuch as a storm begins with warmer 
weather, which hastens evaporation, thus removing the water from the 
tissues. Experimental proofs are furnished by Aderhold's experiments^ 
with artificial rain. In each of six specimens of pears, which had been kept 
for several months in summer in a "rain chamber," five examples were 
found, after a winter frost, to be completely frozen and the sixth partially 
frozen, while of the check plants, which had stood in a dry chamber, only 
2 were frozen and 4 were uninjured. 

Nevertheless, no general rules can be formed in regard to the action of 
wind. Each locality has its own special requirements. If, for example, 
the statement is made that winds act favorably, this refers only to those 
cases where no such permanent effect of the wind is concerned, as is seen 
on sandy coasts. There the action of the roots is the determinating factor. 
Even if they do not freeze, they still cannot take up any more water, while 
the aerial portions still transpire strongly. Plants can directly dry up under 
such conditions. The discoveries of Hofker-Dortmund" are noteworth}"- 
in this connection. He protected the aerial portions less, but covered the 
soil, which in autumn had been loosened up about his plants, with manure 
or damp peat mould and watered the evergreen bushes on sunny frosty 
days. Because of the covering, the frost could not penetrate very far and 
the roots could constantly supply water to the aerial portions. In decorative 
planting, where the finer varieties of conifers are abundantly used, it seems 
advantageous, in v^ry windy regions, to use the bluegreen forms instead of 
the pure green ones. Some growers maintain, in fact, that the former are 
more resistant. 

Care should further be taken that the base of trees or plants, which 
throughout the year have possibly been protected by a moss growth, piles 
of leaves, forest litter and the like, are not exposed in the autumn in clear- 
ing up, etc. It has been found, in fact, that portions of plants matured 
under the protection of soil or leaves, contain a sap which freezes more 
easily than that of portions constantly exposed to the air. Sutherst^ has 
proved this for celery, carrots, and the hearts of cabbage heads. Besides 
this, even if the constitution of the cell sap is not a determinating factor, 
at least the transportation of water is decreased in the roots and trunk 



1 Aderhold, R., Versuche uber den Einfluss haufigen Regens auf die Neigung 
7ur Erkrankung- von Kulturpflanzen. Arb. aus der Kais. Biol. Anst. f. Land- u. 
Forstwirtschaft. Vol. V, Part 6, 1907. 

2 Hofker, Windschutz und Winterschutz. Prakt. Ratgeber i. Obst- u. Garten- 
bau 1907, p. 61. 

3 Sutherst, W. P., Der Gefrierpunkt von Pflanzensaften. Biedermanns Cen- 
tralbl. 1902, p. 401. 



628 

which have been robbed of their protective surroundings ; they thereby cool 
more quickly, thus increasing the danger of drying^. 

The importance of leaving the dead litter of the plants (leaves, bunches 
of grass, flower stalks of the past 3^ear and the like) on seed beds and 
bushes until late spring is not sufficiently appreciated. Not only is their 
effect as a protection against frost concerned here, hut also as a protection 
against the drying spring winds. x\lmost every year we make the discovery 
that plants have come well through a severe winter and evergreens have 
retained their leaves, but if windy, dry weather sets in a few days after the 
snow has melted, the leaves, which had remained juicy, dry up. It is 
possible that, with this rapid drying of the tissues, a similar change may 
take place in the protein of the protoplasma; Gorke'- proved this recently 
to be due to frost action. The result in many plants is a complete case of 
leaf casting disease, which is absent w^here protection has been afforded by 
the litter of the previous year. Often our most common perennial blos- 
soming bushes, grain seeds, tree seeds, etc., are not destroyed until dried 
in the spring. 

d. Smudge.. 

All these preventative methods may not be used universally in agricul- 
ture, but the use of smudges which Mayer^ has rescued from oblivion, may 
deserve still more consideration from the agriculturalist. It was previ- 
ously repeatedly recommended by Goppert* and Meyen^ and supported by 
experiments. Fires which develop a good deal of smoke are ignited on 
the pieces of ground where injury from frost is feared. This process, 
which, according to Boussingault, had been largely used by the old Incas 
in upper Peru and is said to have repeatedly found extensive use among 
the older peoples, is now^ used again as a protection in vineyards. Accord- 
ing to Goppert, Olivier de Serres in 1639 and later Peter Hogstrora in 
1757 endeavored to determine experimentally the effectiveness of the pro- 
cess. In Wiirtemburg as early as in 1796 and in Wiirzburg in 1803, regu- 
lations existed, according to which in the autumn, when danger from frost 
occurred, growers were obliged to light smudges for the vineyards. In 
Griinberg, Silicia, this method was used for a long time, but it was given up 

1 Kosaroff, P., Einfluss verschiedener ausserer Faktoren auf die Wasserauf- 
nahme der Pflanzen; cit. Just's Jahresbericht 1897, I, p. 75. 

- Gorke, H., tJber chemische Vorgang-e beim Erfrieren der Pflanzen. Land- 
wirtschaftliche Versuchsstationen T^VX, 1906, p. 149; cit. Bot. Centralbl. 1907. 
Vol. 104, p. 358. The author explains the cause of death from cold as follows: 
The sap gradually becomes such a concenti-ated solution, due to the elimination of 
water from the cell, in the form of ice, that a precipitation of the soluble protein 
bodies takes place. He bases his theory on experiments with juices extracted 
from healthy and frozen plant parts,, Fresh vegetable sap contained considerablv 
more water soluble protein than that which had been frozen. The degree of cold 
at which a precipitation of the proteins takes place in extracted sap varies greatly 
in the different plant species. In summer barley and rye it fluctuates between 7 to 
9 degrees below zero. In winter barley and rye, between 10 to 15 degrees below 
zero; in the needles of Picea excelsa it reaches 40 degrees below zero. Reactionary 
changes can also cooperate in freezing. The phosphoric acid, for example, as an 
aid, is weaker at higher temperatures, and is stronger when cooled down. 

3 Lehrbuch der Agrikulturchemie 1871, I, p. 382. 

4 Warmeentwicklung 1830, p. 230. 

5 Pflanzenpatholog-ie 1841, p. 323. 



629 

from a lack of general co-operation, despite the fact that, for twenty years, 
it had been used with good success by one proprietor. General co-operation 
in any region is necessary, for otherwise a single proprietor frequently does 
a service to his neighbor upon whose fields the wind drives the smoke, 
without obtaining any service in return. Special regulations for the use of 
smudges are not necessary. Any clear night, toward morning but before 
sunrise, the fires are lighted and fed with damp litter, moss, straw, etc., in 
which care is taken that the thickest possible smoke is carried over the fields. 

Naturally the warmth produced by the fire is not effective here; it 
cannot be felt even a short distance away from the centre of the flame, but 
the smoke, like the straw mats spread by gardeners over the plants, or like 
clouds, is beneficial since it prevents too great cooling from radiation. We 
know from Tyndal's discoveries that a number of substances, like carbonic 
oxid gas, carbonic acid, marsh gas, ammonia, hydrogen sulfid and volatil 
oils, in the finest possible distribution in the air, reduced to a very small 
amount its capacity for letting through rays of warmth. Water vapor^ 
has a like eft'ect. Tyndal determined that this took up an amount of heat 
fifteen times greater than that taken up by the whole (impure) air in which 
it was distributed. The process is, therefore, as follows : — During the day, 
the sun sends its heat to us in radiant and dark rays, part of which the soil 
reflects, but absorbs the greater part, which it retains until the air becomes 
cooler than the soil. When this condition appears an equilibrium of heat 
tends to set in, since the earth now gives up its heat to the cool air in the 
form of dark rays. If, however, the lower layers of the air are strongly 
laden with one of the above-mentioned gases, or with water vapor, the vapor 
itself takes up the warmth radiating from the soil, instead of conducting it 
into the upper regions of the air. Tyndal shows how great the amount of 
heat is, which is taken: up by the lower layers of air. "If we consider the 
earth as a source of heat, at least 10 per cent, of the heat given oft" by it is 
held within ten feet of the upper surface." By this absorption of the dark 
rays of heat the lower layers of the air, rich in water, form a protective 
mantel about the earth which, as a result, does not cool down so far as it 
otherwise would. The smoke produced by the fire is, therefore, an artificial 
covering, full of water vapor, which, in combination with the still partially 
unknown products of distillation, decreases the permeability of the atmos- 
phere for the dark rays given out by the surface of the field. 

We omit a special enumeration of the commercial smoke candles and 
bricks recently made for the purpose of producing smoke at the time of 
frost, since new ones will always appear with the advance in technic ; refer- 
ence to the existence of such articles is sufficient. It need only be mentioned 
that, recently, in smoking vineyards, the smudging material was carried 
about in carts- in order to overcome the blowing of the column of smoke 
by suddenly changing winds. The use of smoke carts is said to be the most 

1 Tyndal, Die Warme betrachtet als eine Art der Bewegung. Deutsche Ausgabe 
von Helmholtz und Wiedemann 1867. 

^ Burger, Raucherkarren. Prakt. Ratg. im Obst- u. Gartenbau 1906, p. 128. 



630 

extensive in the town of Colmar, where a smoke department has developed 
and has been well organized ever since 1884. Colmar lies on a plain and 
the danger from frost is greater on plains than in higher regions, as was 
shown, for example, in 1903 in frosts in Florence. Here Passerini^ found 
fruit trees and asparagus greatly injured at an elevation of 40 m. above 
sea level, but perfectly healthy 100 m. higher. In Colmar iron carts were 
used, which contained possibly 16 litres of fluid tar. After the tar had 
been ignited they were drawn back and forth over one field and then taken 
to the next place (possibly 150 m. distant). When the temperature fell to 
I degree above zero, the smoke department was notified and, at a tempera- 
ture of zero degrees, the signal for lighting was given by means of gunshots. 
As a rule, this began in the night between two and three o'clock. The very 
heavy expense to which the administration was put, because of the smoke 
department, was paid by a tax on the harvested grapes. 

We have cited this special case because we believe that only such an 
organization can have such sweeping results. 

Frost Prediction. 

On account of the expensiveness of producing smudges for the protec- 
tion of plants, threatened by late frosts, it is naturally of the greatest im- 
portance to be able to judge in advance approximately whether night frost 
will occur. 

On this account, it is advisable to make use of the frost curve con- 
structed by Lang (Munich) (Cf. Fig. 150), This is based on psycho- 
metric observations. If, in spring, the temperature falls in the afternoon 
and the sky becomes clear, with a cessation of wind, the probabiUty of night 
frost increases. For the use of the figure, two exactly corresponding 
thermometers are necessary. The mercury bulb of one is so wrapped in 
gauze that the under end of the gauze dips into water, thus keeping the 
cover of the ball moist. This thermometer, because of the constant evap- 
oration of water, will stand lower than the one beside it showing the 
ordinary air temperature. From the difference between these temperatures 
the relative humidity and the position of the dew-point can be reckoned, 
i. e., the temperature at which the water, contained in the air as dew, mist, 
or rain, will be precipitated. In order, however, that these precipitations 
of water vapor may become effective as a protective mantel against frost 
danger produced by radiation, the formation of dew and mist must take 
place at a temperature above zero; therefore, the point of condensation 
must lie above zero. If this is not the case, and the air is dr}', a night frost 
may be expected. 

The mechanical manipulation will, therefore, be as follows : the height 
of the dry thermometer is read first of all, then the difference between this 
and the one with the moist mercury bulb is reckoned. The height of the 



1 Passerini. N., Sui danni prodotti alle piante dal g-hiacciato dei giorni 19-20 
April, 1903. Bull. soc. botan. ital. 1903, p. 308. 



631 



dry thermometer is found on the horizontal Hne and the amount of differ- 
ence on the perpendicular scale. If the two lines, starting from these 
points in the scale, intersect at the right of the curved Une which represents 
the nocturnal frost curve, i. e., intersect among the dotted lines of the scale ; 
then no night frost is to be feared. If, however, the point of intersection 
appears at the left of the hypothenuse of the triangle, i. e.. outside the 
dotted lines, night frost may be expected with certainty, in case the weather 
does not change suddenly and warm air currents do not cause the formation 
of mist or clouds. If, for example, in the afternoon, we find 8 degrees C. 
on the dry instrument and 4 degrees C. on the moist thermometer, this 
gives a difference of 4 degrees. The point of intersection of the perpen- 



Frc 

d 

jC^ 1 ~ 

/\ \ \ \ 


sty Nights 
f--^ 1- _ t _ - 

- - H - -^ 1 


1 - - 

- - T ~ ■ 

L . ^ 

1 


/- 

L _ 
- _ J 
1 


1 1 

t 1 

1 r - - 


6 
5 

4- 
3 
2 

/ 





i 



I 
1^ 



O 1 Z 3 ^ 5 6 7 S 9 fO )l 1Z J3 74 35 
Height of the dry Thermometer 

Fig. 150. Curve for finding night frosts; according to Dr. Lang, Munich. 

dicular temperature line 8 with the horizontal line of a difference of 4 
would be outside the dotted lines, i. e., at the left of the nocturnal frost 
line; therefore a night frost would be probable. 

Hardy Fruit Varieties, 

The more we recognize how manifold are the often outwardly imper- 
ceptible changes due to frost, which becomes apparent only in their after 
eft'ects, the more important becomes the search for varieties of fruit 
resistant to frost. If, however, we compare the experiences of fruit grow- 
ers, it becomes evident that the climatic conditions of different regions may 
modify the character of the variety in such a way that a variety recom- 
mended in one place as hardy is susceptible to frost in another, because of 
earlier development or lesser maturation of the branches. On this account, 



632 

we will name some varieties recommended as hardy for different localities, 
some with a continental climate, others influenced by the sea. In this list 
the injury to the blossom from May frosts is decisive, the condition of the 
wood less important, because injuries to it come under consideration usually 
only in less frequent, heavy winter frosts, while blossoms are exposed every 
year to the danger of freezing. 

The difference between northeastern and northwestern Germany must 
be taken into consideration for German plants. In the eastern provinces 
the influence of Russia is felt, especially in Posen and upper Silesia, because 
of the invading periods of late frost. Nevertheless, we can record experi- 
ences which show that certain varieties of the more sensitive pears furnish 
good table fruit even in Posen. Radowski^ lists from winter pears which 
have stood the test in unfavorable years: Mecheln, Rihas Seedless, 
Madame Verte, Winter Nelis, New Fulvie, Winter William and Dechant 
of Alengon. 

In upper Silesia the following have stood the test- : Amanli's Butter 
pear, William's Christ pear, Bonne Louise d'Avranches, Red Bergamot, 
EngUsh Summer Butter pear, New Poiteau, Pastor pear and Diel's Butter 
pear. - i 

Of the varieties of apple which have grown well in the district Rybnik, 
the following are preferred: Red Astrachan, Oldenburg, Kaiser Alex- 
ander, White Clear apple, Danziger, Hawthomden, Winter Gold Pearmin, 
Landsberg, Baumann, London Pippin and Kasseler. 

The English varieties from the region around Kosel have been espe- 
cially warmly recommended : Lord Derby, The Queen, Lord Grosvenor, 
Lane's Prince Albert, as well as Cellini, Hawthornden and Bismarck. The 
following are suitable for exposed positions and sandy soil : Brunswick 
Milk apple. Red Astrachan, and Oldenburg. According to Mathieu the 
following are especially suitable for the climatic conditions of central Ger- 
many: White Astrachan, Oldenburg, Red Eiser apple. Kaiser Alexander, 
Red Cardinal and, for second choice, Red Astrachan, Prinz (Downing), 
Baumann and Boiken. Of pears, the following have stood the test: 
Winter-Apothecary, Barons B., Dotted Summer Thorn, Green Magdalene, 
Small Long Summer Muscatel, Roman Butter pear. Spar pear. Good 
Gray and Archduke pear^. Although the danger from frost is especially 
great for pears, yet a May frost at the time of blossoming does not always 
destroy the crop. Experience shows that good crops are often obtained 
despite this, because generally only the opened blossoms suffer and those, 
developing later, produce so much the finer fruit. Besides frost, a continu- 
ous rain, at the time of the blossoming fruit trees, is especially to be 
dreaded. 



1 Radowski-Schrimm, Winterbirnen fiir den Osten Deutschlands. Prakt. Ratg. 
i. Obst- u. Gartenb. 17 Dez. 1905. 

- Langer, G. A., Die Bedeutung der Obstsortenwahl, fiir die ortlichen und 
klimatischen Verhaltnisse. Deutsche Giirtnerz, 1905. No. 38. 

3 Jahresbericht d. Sonderausschusses fiir Pflanzenschutz. 1900 Arb. d. D. Landw. 
Ges, Part 60, p. 247. 



633 

For the German climate, the following varieties of plums have, on an 
average, best stood the test: Queen Victoria, Yellow Mirabelle (of Metz), 
Double Mirabelle of Nancy, the German prune and the green Reine Claude. 

Of cherries, the following varieties survive the frosty days of spring 
in spite of their early blossoming: the common sour cherry, Ostheimer 
Weichsel, Double Glass cherry, large, long Loth cherry, and the Red Mass 
cherry. 

For a more moist climate, the varieties might first come under consid- 
eration which would stand the test in Schleswig-Holstein. As such should 
be named the Peach Red Summer apple, Degencr apple, Bath Beauty, Red 
June apple. Summer Spice apple. White Summer Kalvill, William's Favor- 
ite, the White Clear apple, originating from the Baltic provinces of Russia, 
and the English varieties, Mr. Gladstone and Irish Peach (Summer Peach 
apple) ^. 

The majority of the above-named varieties are early apples and we 
think that the cultivation of early varieties must be recommended for the 
conditions in northern Germany. To be sure, they usually do not give first 
class fruit, but, with their shorter period of growth, they have the advan- 
tage of maturing earlier, the growth of their branches thus passing over 
into winter with riper wood which, therefore, is harder. In planting new 
fruit orchards, the varieties should be considered first which have already 
stood the test in a similar climate and under similar soil conditions. It 
should not be forgotten, for example, that varieties, suitable for dry climate, 
usually develop poorly in places by the sea, and conversely. 

In regard to soil conditions, reference should be made to the fact that 
varieties, which grow well on light or on heavy soils, would most advan- 
tageously be chosen from nurseries which have the same physical soil 
constitution as is found in the place where the trees are to stand perma- 
nently. A great difference between the place of early growth and the 
permanent location in which the tree is planted, easily causes an arrestment 
in growth until the specimen has accustomed itself to the new soil condi- 
tions. The conditions are the most difficult in marshy soils, even when 
these have been improved by mixing with lime and the addition of ashes, or 
kainit and Thomas slag. StolP recommends, of the stone fruits, the com- 
mon sour cherry and (with good liming) the house plum. The following 
apples do well. Boskoop's Beauty, Golden Noble apple. Double Pigeon, 
White Winter Dove apple, Boiken apple, Orleans Reinette, Gray Holland 
Reinette, Parker's Pippin and Purple-red Cousinot. The Gravenstein, 
Prinz and the Golden Pearmain grow well but are inclined greatly to canker. 

Only the following pear varieties should be named: the Yat, Chameu 
Delicious and Great Katzenkopf. Of the small fruits, gooseberry and cur- 
rants are planted on moor lands. 



1 Sorauer, Schutz der Obstbaume gegen Krankheiten. Stuttgart, Eugen Ulmer, 
1900, 

2 Stoll, Obstbau auf Moorboden. Proskauer Obstbauzeitung- 1906, p. 3 82. 



634 

Snow Pressure, Ice Coating and Icicles 

Just as certain regions are especially often visited by hailstorms, 
definite zones exist (if from other causes), especially in the mountains, in 
which injuries occur almost every year due to pressure from the snow. 
Besides these zones, some places in all regions with an abundant snowfall 
must be considered as especially endangered. These are depressions in 
the soil into which the snow can be blown from above or from the sides. 
Equal amounts of snowfall act differently according to the weather. If it 
is very cold and windy, enough snow rarely collects on the branches to 
cause injury; the crystals are too fine and cold to stick to one another. If, 
on the other hand, the weather is warm and quiet, the snow falls in great 
flakes and balls easily, large masses cling in the crowns cff the trees and 
bend or break the branches. 

If the trees stand on declivities, many injuries are noticed on the slope 
opposite the windy side; whole strips of trees can be overthrown. This 
occurs as a simple result of snow pressure, especially with mild winter 
weather and soft, open soil, while, with greater cold, the more brittle trunks 
will be broken {snow breakage). Transplanted trees, with shallow root 
systems, are overturned more easily than specimens well anchored by tap 
roots. Evergreen trees are especially inchned to break and of them the 
pines seem most brittle. The tougher varieties, like firs and spruces, bend 
more under the burden and later right themselves. Deciduous trees are 
less injured if the snow masses come after the leaves have fallen. Oaks 
and beeches, which often retain their foliage throughout the whole winter, 
are more endangered than other trees, provided that a previous moist and 
cool summer has not prevented the latter from passing into their dormant 
period and dropping their foliage. Here too the brittleness of the variety 
is decisive for the kind of injury. The trunks and branches of older 
acacias almost always break. In birches and alders, also, breaking may be 
found oftener than bending, Bernhardt^ also calls attention to the fact 
that the resistance of the tree variety changes according to whether its 
habitat is suited to its requirement or not. For our fruit trees, the shape 
of the crown also enters greatly into consideration; especially in apples, 
for with their flat, outspread branches, a true splitting of the crowns is often 
found. If the tree's natural habit of growth does not form a pyramidal 
crown, it is advisable to cultivate artificially the development of a strong 
middle branch. 

With avalanches, occurring frequently in high mountains, the whole 
effect changes according to the variety of the trees and the age of the trunk. 
If the standing forest is old, the trees are broken at different heights and 
thrown together in wild and irregular disorder. Where the trees are of 
different ages, the young trees are only partially pressed downward and, 
for a time, buried in the snow. After the snow melts, these trees right 



1 Waldbeschadigung-en durch Wind-, Schnee-, Eis- und Duftbruch. Centralbl. 
f. d. gesamte Porstwesen 1878, p. 29. 



635 

themselves, or lean somewhat down hill, and slowly continue growth. 
Usually grow'ing branches are found only on the side toward the valley, 
since the rolling snow masses have broken off those of the opposite side. 
In deciduous forests, deformed bushes develop, because of the tearing out 
of the roots or trunks; they look as if produced by the grazing of wild 
animals. 

The influence of the snow covering, and of the accompanying frosts on 
seeds has been mentioned already in an earlier chapter. In regard to 
changes in temperature in the soil, reference should be made to Wild and 
Wollny\ The ice-water, produced by the melting of the snow, can not be 
without effect, as soon as it reaches green meadows and seeded fields. 
Kiister-, for example, has shown that, as a result of cooling with ice- water 
in the chlorophyll grains of Funaria leaves, a vacuole formation is started 
which results in the green pigment's lying at the edge of the vacuoles in the 
form of crescents. 

Ice coating and icicles. The injuries from ice formed on trees are 
more rare. A quickly melting coating of smooth ice is usually considered 
non-injurious. Nevertheless, in general many growers ascribe the produc- 
tion of blasted specks to the deposition of ice on smooth barked branches 
and trunks. If, with Nouel, the production of smooth ice is considered 
as the solidifying of the rain drops due to the impact of striking the tree, the 
drops having already been cooled below zero degrees, it can be assumed 
that the cold of the ice acts injuriously. From the experiences collected 
from artificial frost experiments, I am of the opinion that the smooth ice 
covering can act injuriously, because of changes in tension in the ice-covered 
tissue. It may be proved, in very light spring frosts, that clefts arise in 
the bark tissue of herbaceous shoots without any extensive browning of 
the cell; therefore, without the chemical action of the frost having made 
itself felt. Such injuries to the tissues are also possible from smooth ice, 
if it remains for some time on the plant and especially if it outlasts the 
fluctuations in temperature frequently occurring with the formation of 
smooth ice. 

It is possible to distinguish from the usual formation of smooth ice, 
the ice and mist coverings which might be compared with snow pressure 
because they depend upon different processes of formation. As character- 
istic of the phenomenon, we will consider a description by Breitenlohner", 
who made extensive observations. On January 27, 1879, precipitation 
began in the middle of the day, in a forest near Vienna with a complete 
cessation of wind and with misty weather, under an increasing air pressure 
and low temperature. This precipitation was half way between a drizzle 
and mist and soon hardened to smooth ice. A one-sided ice covering 3 to 

1 Bot. Jahresber. 1898, I, p. 584-85. 

2 Kiister, E., Beitrage zur Physiologie u. Pathologie der Pflanzenzelle. Z. f. 
allg-em. Physiologie 1904, Vol. 4. 

3 Breitenlohner, Der Eis- und Duftanhang im Wiener Walde. Forsch. auf d. 
Gebiete d. Agrikulturphysik 1879, p. 497. 



636 

5 mm. thick was produced on the trees, the temperature of which in all 
parts lay under zero. The period of the still frost lasted 5 to 6 days in 
this Viennese forest ; the ice covering remained 9 days and increased until 
the thinnest branches grew to the size of a ship's rope; the beech trunks 
broke, while the young copse wood was bent to the ground. Since only the 
surface of the soil was frozen, the trees were also overthrown. The 
needles of the conifers especially favored the formation of ice and firs 
became ice pyramids, since the icicles, often 20 cm. long on the upper 
branches, were frozen to the lower branches. 

In low positions, the covering was actually transparent, smooth ice; on 
the heights, however, the chief part consisted of a mixture of ice and mist. 
In the same way, the size of the ice particles decreased gradually from the 
edge of the forest toward the centre, where the covering was neither ice 
nor mist but had a firm, ray-like consistency, until finally, deep in the forest, 
it appeared as a typical mist covering, which became thinner and thinner 
the deeper one penetrated into the forest. In order to form a conception 
of the amount of ice thus produced, which also occurred simultaneously in 
Germany and France, the weight of the ice, hanging on a single branch, 
was determined with the following results : for the one part weight in a 
leafless cherry branch, the ice was 36.7 parts; in the Zerr oak, 44.1 ; in the 
red beech, 85.3; in the fir, 31,1 ; in the spruce, 51.3; in the pine, 99.0 parts. 

Breitenlohner, in explaining the phenomenon, calls attention to the 
fact that the observations of meteorological stations, at the time of the ice 
covering, showed the action of a south wind; therefore, a moist, warm 
equatorial current above a cold polar stream filled the valleys. The contact 
of the equatorial with the polar air waves led to the unusual form of precipi- 
tation. This remained fluid because the lower, cold stream of air was not 
very thick vertically, so that the precipitation, coming from a warm current, 
had to pass only a short way through cold air. 

Where the cold layer of air had a greater vertical thickness, the pre- 
cipitation took on a solid form and covered the vegetation as hoar frost. 

The precipitation, formed after the contact of two layers of air, which 
differ in temperature and moisture, can retain its consistency as fluid water 
even below zero degrees, since moist winds are splendid heat producers and 
carry an amount of latent warmth in water vapor which is freed during the 
continued condensation. Only when the cooling agent exceeds a certain 
amount is the mist changed into frost vapor and then the moisture elim- 
ination consists of ice needles. The peripheral trees', exposed to the free 
currents of air, catch and hold the mist, while, in the interior, the choked 
air causes the formation of the typical mist covering. 

This, therefore, would be analogous to hoar frosty occurring with late 
or early frosts, and, therefore, cannot be considered to be frozen dew. 
Dew is condensed water vapor, which is precipitated in drops on the parts 
of the plant cooled down below the condensation point of the air by radia- 
tion. These drops unite. Water vapor is usually abundantly present in 



637 

the air and, as Stockbridge^ proves, can arise as vapor during the summer 
months from the soil which in the night is warmer than the air. If there 
is a strong dew covering, it can be considered rather as a means of protec- 
tion against the freezing of the plants. If this dew freezes, a crystalline 
coating is produced which is identical with the ice covering. Hoar frost, 
on the other hand, is produced when the point of condensation of the air 
lies below zero degrees. This degree of temperature is reached through 
radiation and evaporation from the plant; therefore, the mist molecules 
attach themselves to one another in a firm crystalline form (soil or summer 
hoar frost). The covering of frozen mist, or winter hoar frost, is pro- 
duced by the flowing of the equatorial current into the slowly displaced 
polar current ; the change is dangerous because, with longer duration, so 
thick a covering of frozen mist can be produced that the strongest trees 
break under its load. 

In nurseries, the prompt and careful beating of the branches with 
sticks will prevent such an injurious accumulation of ice. This naturally 
cannot be carried out in forests. 

In summer frosts, the cultural conditions are often of decisive signifi- 
cance. It should be taken into consideration, in tilled soil, that the plant 
body cools down more rapidly than does the soil which, in the night, acts as 
an equalizing source of heat and prevents, more or less, the formation of 
hoar frost. This efi:'ect will be the greater, the larger the water content of 
the soil which thus retards the cooling down. On damp fields the dew. 
which moderates the cooling of the leaves, is formed earlier and more 
abundantly than on dry soils. On the other hand, cultural regulations 
which prevent the rising of heat from the drier soil layers, such as the 
loosening of the soil, or a strawy manure, favor frost". 



1 Journal of science, Vol. I, p. 471; cit. Naturforscher 1879, No. 32. 

2 Petit, M., Einfluss einiger Kulturverfahren auf die Bildung- von Reif. Annal. 
agron, 1902, No. 7, cit. Centralbl. f. Agrikulturchemie 1903, p. 557. 



CHAPTER XII. 



EXCESS OF HEAT. 



Death from Heat. 

Supported by numerous psychological works\ we have arrived at the 
conclusion that, in judging injuries produced by excess of heat, the same 
points of view make themselves felt as in judging those due to lack of 
heat. In our cultivated plants we are confronted by constantly changing 
organizations. Not only has each species its special requirements as to the 
amount of heat which it can endure, but, even within a wide range of heat, 
the different individuals, in each species, and indeed their different develop- 
mental stages, behave quite differently. The individual susceptibility to a 
degree of heat, exceeding the optimum amount, varies according to the 
habitat, the supply of water and nutritive substances and the action of the 
other vegetative factors so that definite figures as to admissable temperature 
values can only have a limited validity. 

We see, from this, that, in our plantations, the plants can accustom, 
themselves to higher amounts of heat up to a certain degree. Their struc- 
ture becomes different, their development more rapid, but their fife pro- 
cesses, as a whole, still take place within the latitude of health. In regard 
to the different susceptibility of the different organs, according to their 
momentary developmental stage, we favor the theory that the part of the 
plant is the more resistant to an excess of heat, the richer the tissues are 
in cyptoplasm and the relatively poorer in water. Death from heat, like 
death from frost, is produced by the irreparable destruction of the mole- 
cular structure of the cytoplasmic body. We do not know in what way 
this takes place, nor how far a coagulation of certain protein bodies co-oper- 
ates in it. The more porous the cytoplasmic body is within its specific 
composition, due to the in-layering of abundant water, the more easily such 
a destruction takes place. On this account we find that organs, rich in 
water, die more quickly from excess of heat. Death from heat is often 
preceded by a "heat rigor," froni which the plants can recover, when the 
super-maximal temperature abates, and can begin their growth again. The 



1 Pfeffer, W., Pflanzenphysiologie, 2d ed., Vol. II, Leipzig 1904. 



639 

longer the plant is left in a condition of rigor, the more slowly can it take 
up its activity again^ We will become acquainted with other main points 
on the subject of difference in susceptibility in the following actual occur- 
rences. 

Poor Development of Our Vegetables in the Tropics. 

When cultivated plants from the temperate zones are carried to tropical 
regions very- great disturbances become noticeable at times in the ontogeny 
of the plants, which severely impair the cultural aim. This lies in the unde- 
sired abbreviation of the different phases of growth, especially in the 
shortening of the period of leaf development, and of the production of 
reserve substances which are used up too early for the development of the 
reproductive apparatus. This is especially marked in the case of plants in 
which the period of growth has been prolonged by continued cultivation in 
soil abounding in nutritive substances, i. e., rich in nitrogen, and the leaf 
apparatus has been developed luxuriantly (varieties of cabbage, lettuce, 
etc.). We find cases of this nature reported in older works. Thus, for 
example, Duthie cites such a case from Saharanpur-. His experiments in 
India on plant structures show, with a few exceptions, a too rapid ripening 
of the seeds of European plants. While the beet (Beta vulgaris var. rapa) 
takes i8 months in England to complete its development, it needs in India 
only 8 months. In the cultivated forms of German asters, the effect of a 
change of climate manifests itself in the non-ripening of the seed. The 
blossoms of Brachycome and Petunia change and all become white. The 
process seems to me to represent the opposite of the process of the redden- 
ing of plant parts in spring, due to a lack of heat. 

Similar phenomena have been reported from tropical America. Leh- 
man" found in Western Colombia that cabbage, lettuce, onions and carrots 
did not develop sufficiently for cultural purposes. While seeds, imported 
from Europe, furnish in the first year, in corresponding localities, excellent, 
tender vegetables with a desired amount of development, seeds from these 
individuals give plants v^diich, in cabbage and lettuce, show only traces of 
head formation while the onions grow out into stalks a finger thick without 
any tenderness, or flavor. The plants here have no dormant period. 

In the level equatorial regions this phenomenon occurs sooner and 
more noticeably than in the higher, mountainous regions and between the 
loth to 15th parallels of latitude. 

Postponement of the Usual Seed Time in Our Latitudes. 

We must here consider the phenomenon, not infrequently observed, 
that vegetables, sown too late in the year, come into the hot, dry season too 



1 Hilbrig> H., tJbei' den Einfluss supramaximaler Temperatur auf das Wachstum 
der Pflanzen. Inauguraldissertation. I^eipzig- 1900; cit. Just, Bot. Jahresber, 1901, 
II, p. 203. 

2 Gardener's Chronicle 1881, I, p. 627. 

3 Lehmann, tJber eine physiologische Erscheinung bei der Gemtisekultur im 
tropischen Amerika. Deutsche Gartnerzeitung 1883, p. 260. 



640 

soon, while still developing their vegetative organs. The leaf-body becomes 
hard and the tuber-like swellings soon become woody. Annual seed-bear- 
ing plants (grains and summer blossoms) ripen prematurely. Peas, sown 
too late, succumb very early to rust (Uromyces). Kraus^ has already 
advanced the theory that the turgidity of the tissue decreases with too high 
temperatures. 

Haberlandt, in his experimental plants, has found a splendid example 
of the influence of drought in fungous attacks on plants. Of three pots 
sown with wheat and left standing side by side during the whole period of 
growth, the one where the plants were watered only enough to keep up 
life, were so attacked by mildew (Erysiphe graminis) that the greater part, 
at any rate, of the blame for the whole failure of the harvest must be 
ascribed to the fungus. The pot, standing nearby and abundantly watered, 
was almost entirely shunned by the parasite-. Still more decisive is the case 
which I observed with Podosphaera leucotricha Salm. Half of a number 
of young apple trees in pots stood in a conserv^atory, the other half out of 
doors back of this conservatory. All the specimens had retained through- 
out the winter the oidia form from the previous year. The trees in the 
conservatory exposed, without any protection, to the summer heat were 
twisted out of the shape from the extensive spread of the mildew, which 
developed to the perithecial fruiting stage. Those standing back of the 
conservatories, in half shade and in moving air, lost the mildew. Hell- 
riegel's^ experiments prove how much the production of plants suffers from 
a wrong time of sowing, even without the action of parasitic enemies. 
Barley sown in April, May, June, August and September in pots with the 
same mixture of nutritive substances and soil moisture, under otherunse 
entirely similar conditions, behaved absolutely differently. That sown in 
April developed very regularly grown, excellent plants, bearing ripe seeds 
at the end of 88 days. The seed sown at the end of May grew into plants 
which, at first, also developed very vigorously, but as a long period of heat 
occurred toward the middle of July, at the time the heads push out from 
the upper leaf sheath the stalk was retarded in its growth in length. Up to 
the premature death of the plants (after yj days) the kernels had matured 
only incompletely and remained flat ; they, therefore, had become ripe pre- 
maturely. The latter sowings showed an increasing lengthening of the 
period of growth (the September seed, for example, required 240 days) and 
resulted in quite incompletely ripened grain. 

In regard to forest plantations, experience also shows that the losses 
from transplanting of young forest trees vary according to the time it takes 
place. Experiments in Mariabrunn* gave the smallest loss in spring trans- 
planting. For spruce trees the number of dying examples of an April to 
June planting increases only to decrease again in autumn transplanting 



Molekularkonstitution des Pix)toplasms. Flora 1877, p. 534. 
Biedermann's Centralbl. 1875, II, p. 402. 
Grundlag'en des Ackerbaues 1883, p. 352. 
Deutsche Forstzeitung November 13, 1892. 



641 

(September and October). The same behavior was shown in the case of 
the pine, which gave a still more significant percentage of loss. In decidu- 
ous trees, as is well known, autumn transplantation is preferred. 

Sunburn of Leaves tn Nature. 

The death of the tissue, resulting from the action of the sun, is here 
meant. In such cases, however, light and warmth act together. We do 
not know how much must be ascribed to each factor in such phenomena of 
death. The opinion of noted foresters, that all the Hght in the plant cell 
passes over into the dynamic force of heat and becomes effective in this 
form, is not very probable. My evaporation experiments with a decrease 
of light, and a simultaneous increase in temperature, indicate rather that 
at least a part of the light, as such, becomes effective, and influences the 
process of assimilation. A part without doubt is converted into heat and 
acts in that way. Upon this hypothesis, it is also probable that a plant 
would behave differently with the same amount of heat, according to 
whether it is subjected to this in a dark, or in a lighted place. 

In general, temperatures between 40 to 50 degrees C. are fatal; yet 
Askenasy^ has observed, with Crassulae, that they can endure uninjured 
such amounts of heat. Askenasy was convinced in midsummer that the 
inner parts of Sempervivum, at an atmospheric temperature of 31 degrees C. 
in the shade, had undergone a heating up to 48 to 51 degrees C. The 
warmth within the plants seemed higher in some varieties, lower in others, 
than on their outer surfaces. The temperature of the outer surface of the 
leaf, in different days, did not stand in any direct relation to the atmospheric 
temperature. Sempervivum arenarium showed, for example, 

at 31.0 degrees C. on the isth of July, at 3:00 P. M., 48.7 degrees C. 
" 28.2 " " " " i6th " ' " "3 :oo P. M., 46.0 
"28.1 " " " " i8th " " " 12 :30 P. M., 49-0 

Thin-leaved plants, standing nearby, had a much lower temperature. 

The phenomena of sunburn are observed most frequently in hot-house 
plants which, in spring, are set out of doors. The leaf is not always killed 
but often only reddened or browned. In curled leaves only the convexity, 
on the upper side, becomes colored and, instead of being green, is reddened 
to a copper color (roses). In the course of a few weeks such a plant can 
recover even when left in this place. 

I tested experimentally a similar case in spotted specimens of Canna 
indica, the greatest number of which in cloudy weather were taken from 
the hot house, in which they had been forced up to the unfolding of the 
first blossoms, and were set out of doors. Some pots stayed two days 
longer in the hot house and were then sunk in the earth in the middle of the 
day beside the specimens set out earlier. In the afternoon the upper leaves 



1 Askenasy, tJtaer die Temperatur, welche Pflanzen im Sonnenlichte annehmen. 
Bot. Zeit. 1875, p. 441. 



642 

appeared striped with white, since the parts of each intercostal field farthest 
from the ribs, conducting water, showed dead tissue. . The white stripes 
were broadest at the edge of the leaf and dwindled gradually toward the 
midrib so that it was clearly evident that the burning of the leaf occurred 
earliest and strongest in those regions which lay farthest away from the 
water conducting system of the large vascular bundles. 

The epidermis did not seem essentially changed in the white places, 
but the palisade parenchyma which no longer had chloroplasts was greatly 
changed, while a transitional zone toward the healthy tissue, provided with 
large chlorophyll bodies arranged along the w'alls, showed a content still 
green but cloudy. In tissue, which had become white, the cell walls of 
which had remained clear, glycerin contracted only a small amount of the 
contents so that it w^as necessary to conclude that in this short time a large 
part of the contents had been used up in respiration. In the places most 
greatly injured, the epidermis v/as raised here and there, like blisters, from 
the flesh of the leaf (burn blisters) and the destruction of the chlorophyll 
had extended even to the under side of the leaf. After some weeks it was 
possible to observe a regeneration of the chloroplasts in the burned leaves 
in the above-mentioned transitional zones. Thus, a healing process had 
taken place exactly as after slight injuries from frost. The presence of 
mycelium could now be demonstrated beneath the burn blisters in which 
part of the epidermal cells seemed to have collapsed. 

Rowlee^ observed a collapse of the epidermal cells even after an 8 hour 
exposure to electric arc light which acted on the leaves of heliotrope at a 
distance of one metre; other plants (for example Ficus elastica). under 
similar conditions, remained unchanged. 

In fleshy, long-lived leaves, the healthy tissue is separated from the 
burned tissue by a cork zone, as is shown in the subjoined illustration of a 
Clivia leaf injured in August from sunburn. It is easy to observe that the 
position of the leaf determines the place of production of the burned spot, 
since only those places, perpendicular to the source of heat, turned a yellow- 
ish gray and collapsed. On the following day the burned spot was per- 
fectly brown and brittle. The yoimgest leaves were uninjured. The 
boundary between dead and living tissue becomes sharp, as soon as the 
burned spot extends through the whole thickness of the leaf. If, however, 
only the upper side of the leaf is injured, a faded, transitional zone is found. 
In this, the chloroplasts turn the color of verdigris, while the remaining cell 
contents show a yellow green. Therefore, there may occur here first of all 
the disappearance of the xanthophyll, while the cyanophyll remains com- 
bined in the chloroplasts. Thus, the contours of the mass of chlorophyll 
grains, which at first refracted the light equally strongly, become less sharp 
and a large amount of very fine granules give it a sandy consistency. 



1 Rowlee, W., Effect of electric light upon the tissues of leaves. Just's bot. 
Jahresber, 1900. II, p. 287. 



643 

Finally, the chloroplasts form groups, a dirty tea-green to a blackish green 
in color, which assume a cord-like form because the cell collapses. These 
content masses, which lie against a wall, bleach very quickly in sunshine 
and cause the yellowish gray color of the burned place. The cell walls do 
not lose their cellulose character, as is proved by testing them with chlor 
zinc iodide. 

The healthy tissue begins at once to cut itself off from the injured 
tissue by a cork zone (k) whereby the cells of the transitional zone (br), 
which have remained rich in contents, at first somewhat enlarged by an 
undulation of their walls (h^ s), show enlarged intercellular spaces and 
gradually die. 

When the burned spot becomes somewhat older, it turns a deeper 
brown, in which the epidermal cells, which have not collapsed (e), partici- 
pate even up to the healthy tissue. The cork zone (k) is produced by a 




Pig. 151. Cross-section through a sunburn spot in a leaf of CM via nobilis. 



division and elongation of the mesophyll cells which have remained alive at 
the edge of the burned place. The normal cells, back of these (p) usually 
remain somewhat poorer in chlorophyll. The callous appearance of the 
peripheral zone (w) of the normal leaf part at the edge of the 'burned 
place should be noted ; this is explained by the distention of the cells, which 
develop the cork zone, and of the mesophyll (h) lying in front of them, 
which had been injured but did not die at once. 

Sunburn Spots in Conservatories. 

Complaints of the occurrence of burned spots on the leaves of tender 
plants in conservatories abound, especially in spring, and opinions as to 
their production differ greatly. Sometimes bubbles in the glass are held 
responsible for this. Sometimes, it is thought that the drops of water, 
which remain on the upper surface of the leaf after the plants are sprinkled, 
act as burning glasses or become so warm from the sunshine that they injure 



644 

the tissue. Jonsson's^ experiments have proved that the bubbles in the 
glass are actually the cause. He observed the light image of the sun's rays 
produced on the leaf b}^ such bubbles and the changed position of such 
spots resulting from the change of the sun's position. This explains also 
the not infrequently observable phenomenon that such burned spots appear 
in regular lines. 

One experiment proved, however, that sprinkling can also act danger- 
ously, when a drop of water remained hanging on the under side of the 
cover glass, fastened at some distance above the surface of the leaf. In 
this, traces of burned spots could be produced, while drops of water lying 
directly on the leaf caused no injury. 

To avoid such disadvantages, it would be advisable in general practice 
to choose better grades of glass at least for those hot houses in which valu- 
able foliage plants are kept. 

Defoliation. 

Phenomena of scorching are not here concerned but rather the precipi- 
tous maturity of the tissues. In cases observable out of doors, a great 
dryness of the soil is usually combined with the direct action of the sun. 
Special experiments with burning glasses show, however, that even in 
damp soil the leaves are thrown off which are most strongly injured by 
burned spots. Wiesner^ found that, in "the falling of leaves due to heat," 
those which usually fall come from the inner part of the crown of the tree, 
rather than from its periphery. He thinks that these outer leaves, as a 
result of their greater radiation of heat, do not become so warm as the 
leaves found in the enclosed places. We might seek the reason for this in 
the different vitality of the organs. Those exposed to the greater amount 
of light produce more substance and their cells are richer in cytoplasmic 
material. They have, therefore, with an abnormally increased evaporation 
and respiration, more resen^e substances and are longer lived than leaves 
of the same period found in the inner part of the tree crown. Young 
organs in themselves are more resistant. 

In cases occurring out of doors, the place of growth, together with the 
water supply, acts decisively. Among forest trees, this is seen best in oaks 
and larches in young plantations where individual specimens, already show- 
ing completely dried bunches of leaves, are always to be found between 
green trees which have been uninjured, or only slightly changed. 

In one young larch plantation, I found that the specimens most greatly 
injured had lost almost all their needles from the upper branches. Only the 
very young shoots, the tips of which seemed twisted and a fox red, still held 
needles which hung downward like red tassels. The youngest needles of all 

1 Jonsson. Bengt, Om Brannflakar pa vaxtblad. Botaniska Notiser 1891 
Zeitschr. f. Pflanzenkrankh. 1892, p. 358. 

2 Wiesner, Jul., t^ber den Hitzelaubfall. Ber. d. D. Bot. Ges. 1904, Vol. XXIT, 
p. 501. 



645 

seemed faded, flattened and papery dry. Their extremely scanty cell con- 
tents formed a colorless ball, lying free in the inner part of the cell and 
turning yellow with iodine. In the older needles, the cell walls of which 
had remained perfectly colorless, the abundant cell contents appeared in the 
form of pale grayish red, or yellowish brown, uniform masses lying against 
the wall. The appearance resembled that produced under the influence of 
acid gases. In spruces too the discoloration of the needles, produced by 
intense summer drought, is very similar to that produced by sulfurous acid. 

A similar dropping of the leaves, due to heat and drought, may also 
occur not infrequently in other conifers, especially when suddenly left 
standing alone. My experiments with spruces showed, in regard to the 
process of dropping needles, that when the rays from a lens were focussed 
at the base of the needles, these could be loosened at once with a slight pres- 
sure even if they showed no discoloration. When the needles were injured 
at points higher up they remained attached. In the burned places the cell 
contents had contracted into a band-like, green to brownish-green mass in 
the centre of the cell, and even their granular structure could still be per- 
ceived. The contracted content masses lay usually in the same position in 
the different ceUs, i. e., in the direction of the long diameter of the needle. 

Injuries to the bud from sunburn are comparatively rare. This is to be 
attributed, in part, to the protection of the covering of the buds by a hairy 
felt, gum, resin, cork layers, or the like, which often are found to be espe- 
cially effective; in part, also to the abundant cytoplasmic contents of the 
young tissue which, therefore, are changed with greater difficulty. In the 
tropics, special protective precautions may often be found. According to 
Potter \ for example, in Artecarpus, Heptapleurum, Canarium ceylanicum, 
and others, the stipules of the older leaf organs serve as a protection for 
the young leaves until they become strong, or the entire old leaf at first 
forms a protective covering for the young one (Uvaria purpurea, Gos- 
sypium, etc.) 

In peach forcing in England, a dropping of the peach buds has been 
observed. In places, where a damp cloth was stretched over the plants as 
a protection against the action of the sun, no dropping of the buds was 
found^. 

Sunburn in Blossoms and Fruits. 

In injuries to blossoms, no absolutely high degree of temperature is 
necessary; even the usual temperatures can become injurious for shade 
loving plants in an unfavorable place of growth. The tuberous Begonias 
form the best known example, the blossom edges of which easily become 
brown, if the plants cannot benefit from the evaporation from moist soil. 

An unusual excess of heat affects fruit in two ways. On the one 
hand, it produces premature ripening, i. e., the appearance of the processes 



1 Potter, M. C, Observations on the Protection of Buds in the Tropics. Journ. 
Linn. Soc. XXVIII, 1893, p. 343. 

2 Gardener's Chronicle 1893, XIII, p. 693. 



'646 

of ripening at a time when the fruit should really be storing up reserve 
substances. The result is that the cells of the fruit flesh, insufficiently filled 
with reserve substances, end their life prematurely, resulting in a specked 
condition and premature decay when stored. In grains, a premature 
ripening of the blades causes a distinct injury to the kernel from an insuffi- 
cient formation of starch^ 

The other form of injury consists in the direct killing of the tissues, 
by sunburn, on the exposed places of juicy fruits. Such burned spots fre- 
quently resemble places injured by hail because the killed tissue cannot 
stretch proportionately during the process of swelling of the fruit and 
therefore tears. In the increasing cultivation of the tomato, we now find 
abundant examples which remain unrecognized only because fungi usually 
infest the burned places of the fruit. The cases are then described as 
parasitic diseases. 

Injury to Grapes from Sunburn. 

This is of great agricultural significance. According to Miiller- 
Thurgau's observations- an injury to grapes will be observed when hot, 
clear, sunny days occur suddenly after a longer period of cold, damp 
weather. It is found then, almost as a rule, that the berries of the free 
hanging clusters, exposed to the direct rays of the sun, lose their green 
color, become pale, then turn brown and finally shrivel. The stem of the 
cluster also begins to suffer where it is directly touched by the sun's rays. 
The berries, hanging to it, shrivel but, in this case, do not lose their green 
color. In the blue varieties, the berries, which come in contact with the 
sun's rays, remain green, becoming darker than those of the white varieties 
and turn almost black. In some years, whole bunches are found shrivelled 
up like raisins, producing in places a considerable injury^. That it is 
actually an excess of the heat which kills the berries in this case is shown 
by the fact that grapes, which were warmed in a tin case to 50 degrees C, 
took on exactly the same appearance as specimens attacked by sunburn out 
of doors. The state of ripeness, as well as the water content of the organs, 
and also the humidity of the surrounding air, exercises a decisive influence 
on the burning. Unripe Riesling and Sylvaner berries were not injured 
when warmed to 42 degrees C. for two hours but were injured at 44 degrees 
C. after an equal length of time. 

Direct measurements showed that the berries, on which the sun shone, 
were warmer than the surrounding air. While a thermometer in the air 
showed 24 degrees C. in the shade and another 36 degrees C. in the sun, the 
temperature in the grapes, exposed to the sun, increased to 40 degrees C. 

It was found further that Riesling grapes from good warm positions 
were poorer in water and suffered less from sunburn, than those from 



1 Deherain et Dupont, tJber den Ursprung der Starke des Weizenkorns; cit. 
Biedermann's Centralbl. 1902, p. 324. 

2 Der Weinbau 1883, No. 35. 

3 Jahresber, d. Sonderaussch. f. Pflanzenschutz 1892. Arb. d. D. Landw. G. 



647 

inferior vineyards. Besides the small water content, the advanced ripeness 
of the berries is a condition which acts as a protection against sunburn. 
The early Malinger and the early Burgundy, which ripen even in the middle 
of August, for example, showed no injury whatever from the hot August 
sun while more than 50 different varieties of grapes, standing close by, 
which ripened later and therefore were still hard and green in August, had 
suffered more or less. Measurements of the temperature in green, unripe, 
hard berries of Riesling, • Sylvaner, Elbling and late Burgundy showed 
injury at 43 degrees C, while the fairly ripe berries of the early Malinger 
and early Burgundy could be warmed for some time up to 55 degrees C. 
without injury and the flesh of the Malinger grapes was killed only at a 
temperature somewhat above 62 degrees C. 

The discovery by practical workers that sunburn is found most fre- 
quently when wet, cold weather precedes hot days, is explained, on the one 
hand, by the greater water content of the berries and, on the other, by a 
lesser evaporation and, consequently, a lesser cooling when the air is moist. 
In regard to the influence of drought, Miiller made an experiment on two 
Riesling grapes, one of which was placed in a glass vessel lined with moist 
blotting paper, the other in one containing some calcium chlorid, and both 
placed in a tin case which could be heated. The grapes in moist air were 
completely killed at a temperature of 41.5 degrees C, while those in the air, 
dried by the calcium chlorid, were scarcely injured. Two thermometers, 
one of which hung free while the bulb of the other was stuck into a grape 
berry, were put in a similar tin case, and warmed up to 40 degrees C. The 
thermometer, covered by the grape, constantly stood approximately 4 de- 
grees lower than the other when the temperature increased slowly as well 
as when it decreased. This may well be conditioned only by the evapora- 
tion of the grape. 

The phenomenon of Seed cracking can set in as the result of sunburn. 
Since, however, different causes of this phenomenon exist, it would be 
better to consider it later by itself. 

At times so called "rusty grapes" are found, i. e., those of which the 
skin has formed fine cork lamellae. This has been thought to be a protec- 
tive means against sunburnt 

Protection of the grapes by the leaves is the best precautionary method 
and it is wrong to think grapes are helped by the removal of their foliage. 

Sun Cracks. 

In forest and other trees, at times in spring, the bark cracks. This 
phenomenon has been named Sun cracks by de Jonghe, while Caspary^ 
considers them due to the action of frost. Surface dying of the bark is 
distinguished, as sunburn, from simple torn wounds. Illustrations are found 



1 Zeitschr. f. Pflanzenkrankh. 1902, p. 111. 

- Bot. Zeit. 1857, No. 10; "Bewirkt die Sonne Risse in Rinde und Holz der 
Baume?" 



648 

in R. Hartig^ and Nordling-. The latter distinguishes still another "winter 
sunburn"^ in which the injury to the trunk is found only at its base. The 
reflection of the sun's rays from the upper surface of the soil is assumed to 
be the cause. R. Hartig's illustration shows the lower end of the trunk of 
a red beech sapling with sun cracks*. Since these phenomena, as yet, have 
only been observed in the late winter and strict experimental proofs are still 
lacking, we maintain the opinion expressed earlier that the cracks are pro- 
duced by differences in tension which arise with a sudden sharp change in 
temperature without the necessity of a warming of the tissue from the sun 
until it dies, as is the case in sunburned places. Hartig's" measurements of 
a spruce in August show how much the parts of the plants are warmed 
above the temperature of the air. With an air temperature of 37 degrees 
C. he found 55 degrees C. in the cambial region of the southwest side; only 
45 degrees C. on the south side ; 39 degrees C. on the east side ; 37 degrees 
C. on the north side. The measurements were made in the afternoon 
after 4 o'clock. 

Influence of Too Great Soil Heat. 

Sachs'^ has already furnished abundant material in regard to the deter- 
mination of the temperature requirements of diiTerent plants and especially 
with respect to the germination of seeds which had been exposed to a high 
temperature of air and water. In the latter connection it is evident that 
dry seeds endure a higher temperature without being injured than those 
already sprouted and that probably all plant tissue (within boundaries 
required by the species) is in every case the more resistant to heat the less 
the water content of the cells is proved to be. Corroborative works have 
been furnished by Haberlandt, Wiesner, Fiedler, Krasan, Just, Nobbe, 
Hoehnel and recent authors, in regard to which reference must be made 
to Pfeffer's Physiology. 

Just's^ experiments show, for example, that unfavorable results may 
be experienced when, in germinating seed, the temperature is increased 
above the optimum given for any special variety. He found in these ex- 
periments, that a prolongation of the germinating time and a slower devel- 
opment of the seedling is produced by too high temperatures, just as in 
seeds which are too old, 

Prillieux's* older work is of importance in regard to the anatomical 
changes. In bean and pumpkin seeds, sown in pots in which a high soil 
temperature was maintained by heated wires, the following results were . 
found: the young seedlings grew but little and Avith difficulty; however, 

1 Lehrbuch der Baumkrankheiten, Ist ed., p. 188. 

2 Lehrbuch des Forstschutzes, 1884, p. 332. 

3 Baumphysiologische Bedeutung des kalten Winters 1879-80; cit. Illustrierte 
Gartenzeitung 1881. 

4 Lehrbuch der Pflanzenkrankheiten, 3d ed. 1900, p. 230. 

5 Ibid., p. 228. 

6 Experimental-Physiologie, p. 64 ff. 

7 Cohn's Beitrage zur Biologie der Pflanzen. Vol. II, p. 311. 

8 Prillieux, Alterations produites dans les plantes par la culture dans un sol 
surchauffe. Ann. sc. nat. Ser. VI Botanique, t. X, p. 347. 



649 

they looked swollen ; in the places where the swelling of the little stems was 
most intensive, gaping, usually horizontal wounds were found which ex- 
tended to the pith. In contrast to normal plants of the same age, those of 
the over-heated soil were only half as long but approximately three to four 
times as thick in diameter at the place of the greatest swelling. Here too 
the epidermal cells were two to three times as broad as in normal plants. 
The stomata showed the same difference only to a slighter degree. The 
hairs were not changed. The bark parenchyma was, to be sure, four times 
as thick but no cell increase had taken place ; the cells of the pith paren- 
chyma showed still greater radial distention ; but actual cell increase could 
be proved only in the bast parenchyma. Prillieux cites further that the 
nuclei behave similarly. They hypertrophy and increase in such a way that 
even three or four may be found in a single cell. Nuclear division takes 
place by fragmentation. Such a cell increase is perceived also in the short, 
curved and twisted, but not swollen, roots of the changed plants. The large, 
deformed nuclei show usually very irregular nucleoli, occurring more than 
one in a cell, in which, not infrequently, vacuoles appear when colored black 
with osmic acid. In fragmentation of the nuclei, first a fold usually ap- 
pears at one side and seems to constrict the nucleus. Later a cytoplasmic 
wall is formed between the two resulting nuclei. The two halves, thus 
produced, become inflated and tend to separate, which separation, however, 
does not always actually become complete. It also seems that this cleavage 
of the nucleus takes place within an already existing cytoplasmic covering, 
belonging to the original nucleus, which does not rupture until later. 

This increase of the nuclei and the tender bast element may indeed 
indicate the way in which a higher soil temperature, which approximates 
the optimum, can act favorably. Cell increase and the conducting of the 
plastic material may be hastened. As is well known, horticulture makes 
good use of the beneficial influence of the higher soil temperature by means 
of hotbeds. Yet just here the observation may be made, that a too high soil 
temperature is not favorable for the many plants from a cooler climate. 
They do not grow more rapidly but easily decay. The assimilatory energy 
slackens and the weakened organism is attacked by bacteria and fungi. 
Hellriegel's experiments^ show how much assimilation falls when the soil 
temperature becomes too high. Comparative cultures in roasted quartz 

sand gave yields for 

rye 

at 8° 10° 15° 20° 25° 30° 40° C. constant soil temperature 

Fresh weight 191.5 176.3 269.4 456.6 376.0 408.0 240.1 

Dry substance . . 23.9 22.8 32.4 49.5 42.4 47-0 31.2 

wheat 

Fresh weight 98.6 130.8 241.0 260.5 342.0 402.2 296.0 

Dry substance .. 15.8 20.8 29.5 30.8 43.9 46.9 40.3 

barley 

Fresh weight 151.9 156.0 383.4 408.5 435.2 365.,0 230.5 

Dry substance .. 17.1 18.0 34.4 36.7 42,0 35.0 26.3 



1 Beitr. zu den naturwissenschaftlichen Grundlagen des Ackerbaues. Braun- 
schweig 1883. Vieweg & Sohn. 



650 

The results refer to young plants and show clearly how the production 
falls off toward an upper and lower limit starting from an optimum tem- 
perature for the roots. At the same time the figures also throw light upon 
the difference in the warmth needed by the different species. Wheat (at 
least when young) requires the highest soil temperature. Wheat developed 
the most energetic assimilatory activity at 30 degrees soil temperature, while 
rye developed best at 20 degrees and barley at 25 degrees C. 

Also in this young stage, when adjustment to conditions is easiest, the 
plants clearly show the disturbing influence of too high a soil temperature. 
Aside from the retardation of germination, a considerable difference was 
shown in the habit of growth of the seedlings in that their stems and leaves 
at high temperatures became thin and delicate while, at lower soil tempera- 
tures, the specimens appeared short, thick and more fleshy. 

The experiments by v. Bialoblocki^ gave the same results and showed 
also considerable differences in the formation of the root system. The 
barley plants, which were kept growing constantly at 10 degrees C, soil 
temperature, had formed their roots from a few^ large, strikingly strong, 
splendidly white branches of the primary and secondary series, of which the 
latter were unusually short and covered with small, wart-like protuberances 
(latent eyes of the tertiary series). The individuals, standing in the soil at 
30 degrees C, constant temperature, had developed unusual, richly ramified 
brown root fibres, as thin as threads, which had become matted to a thick 
felt. At 40 degrees C. the character of the root ball was the same but its 
extent was very small ; a small felt was formed in the upper soil layers. 

Tolsky- also found in oats a stronger development of the individual 
roots at a lower temperature and recently Kossowitsch^ confirmed these 
results. The rate of penetration of the oats roots into the soil was retarded 
thereby. A soil layer of about 30 cm., at the increased temperature, was 
penetrated 14 days after seeding but, at the lower temperature, only after 
30 days. 

Also in other experimental plants (mustard and flax) the weight of the 
air dried roots was the greatest at a low temperature. The amount of 
evaporation of plants grown under such conditions was less than for speci- 
mens of similar development which had grown at the normal, or higher 
temperature. 

Failure of the Pineapple. 

The fact, that pineapples grown in European conservatories surpass 
imported fruit, because of increased flavor, has extended their cultivation 
in private gardens in some regions (for example, Silicia). The greatest 
danger in their cultivation lies in their "Durchtreihen," i. e., a continued 
leaf growth at a time when the plant should enter its rest period in order 

1 Landwirtschaftliche Versuchsstationen 1871, Vol. XIII, p. 424. 

2 Journ. f. experim. Landwirtschaft, 1901, p. 730. 

:! Kossowitsch, P., Die Entwickelung der Wurzeln in Abhangigkeit von der 
Bodentemperatur in der ersten Wachstumsperiode der Pflanzen. Journ. f. experim. 
Landw. 1903; cit. Centralbl. f. Agrkulturchemie 1904, p. 451. 



651 

to set fruit. The cause lies in the untimely supply of heat and water during 
the rest period of the plant, which needs three years for its development. 
After the plants from the sprouts (suckers) of already fruited plants have 
grown for two years in hot beds, they are planted in the autumn of the 
third year in beds close under the glass of greenhouses which are built flat 
purposely for pineapple growing. These beds are kept at a high soil tem- 
perature by bottom heat. When the plants are well rooted at a temperature 
which should lie between 25 to ■z'j degrees C. the heat must be decreased at 
least 10 to 12 degrees C. and a marked, dry period begin. Only if the 
plants have thus been given a complete rest, may the forcing begin again in 
February, when the former degree of heat in the soil is allowed to act again 
on the plants and the soil very soon well watered with warm water. If, 
after 4 to 6 weeks, the leaves of the plants begin to spread out and to 
become colored at the heart, it may be concluded that the fruit is setting. 
For fear that the decrease of temperature may injure the pineapple the 
moisture and heat are often not sufficiently reduced and the result is a 
continued growth of the plant with the exclusive production of leaves. 

According to reports made by Cousins^ the same phenomena appear in 
the cultivation of the pineapple in the tropics. 

The Classiness of Orchids. 

Two cases may be briefly mentioned here in which plants of Oncidium 
developed young shoots, nearly all of which showed a glassy, translucent 
consistency. A few days after the appearance of the glassy places, at the 
base of the bulbs, the shoots fell over and decayed. Since parasites could not 
be found in the initial stages of the disease and the slenderness of the older 
shoots indicated great heat and moisture, the plants, without any further 
treatment, were brought into a cooler, brighter conservatory. After a few 
weeks, the phenomenon had disappeared. 

Failure in Forcing Blossom Bulbs. 

Often, after very hot summers, gardeners complain that, contrary to all 
expectations, the blossom bulbs develop poorly; that, when the usual tem- 
perature was used, the blossoms pushed unsatisfactorily out of the bulbs 
and these began to decay. Bulbs set out later than usual for forcing and 
cuhivated with less heat, however, gave perfect blossoms. 

From the different cases with which I have become familiar, I have 
formed the following theory: if a period of warm weather occurs in the 
early summer, when the bulb fields are in the midst of their most vigorous 
development, the foliage is killed prematurely by heat and the bulb becomes 
ripe prematurely. Under such circumstances, the material which later, in 
forcing, should furnish the starch dissolving enzymes, seems to be formed 
in insufficient amounts. If, in forcing the bulbs in winter, the usual high 

1 Revue cult, colon. 1902, No. 92. 



652 

temperature is made use of at the customary time, the stimulus of the heat 
for these prematurely ripened bulbs is too great, since they require a slower. 
more gradual sprouting with lower temperature. If this requirement is not 
taken into consideration, the reserve substances are not used, as normally, 
in nourishing the inflorescence and the bulbs decay. 

Another case in which similarly, the usual forcing method fails, be- 
cause the temperature usually found to be best proves to be too high, is seen 
in the "falling over of tulips." In certain early varieties (pink blooming), 
it has been observed that the peduncles break over before the blossoms open. 
A glassy spot i to 2cm. long, appears below the node out of which leaves 
spring in these varieties (several centimeters above the neck of the bulb). 
The gradual shrivelling of this spot causes the breaking over of the stem. 

Investigation proved an abundance of starch throughout the whole 
bulb body along with an unusual amount of peroxydases. In forcing, it 
was found, however, that with a high increase of temperature, the starch 
was insufficiently dissolved, i. e., too little constructive material was sup- 
plied to those forced aerial parts. The medullary tissue of the stalk, poor 
in contents, was torn at this glassy place, because of the rapid elongation, 
thus destroying the rigidity of the stalk. Bulbs, from the same shipment, 
which were set out some weeks later, i. e., nearer their natural time of 
developing and in the same temperature, developed normally. It is thus 
seen how the same temperature in the conservatory can act favorably at 
one time, unfavorably at another, according to the weather of the previous 
year and the constitution of the bulbs, and it is advisable at the beginning 
of the time of forcing to make some preliminary tests. 

In lilies of the valley, the same circumstance of unusually rich starch 
production with an insufficient supply of starch dissolving enzymes mani- 
fests itself in the scanty development of the blossom sprays. At first only 
a few of the lowest blossoms of the sprays develop and only after these 
have withered do the upper bells open. For this reason, forced lilies of 
the valley often become unsalable as market plants. For such cases the 
process used by Garden Inspector Weber^ of Spindlersfeld can be recom- 
mended. He watered the pips with water at 44 degrees C. before planting. 
At any rate, the dissolving of the reserve substances was hastened by this. 

It is evident from these examples that the dormant plant parts must 
have reached a definite condition of maturity for success in forcing, which 
condition is characterized by a sufficient supply of starch dissolving enzymes. 

Seed Which Has Suffered From Self Heating. 

Without going into the much mooted question whether the self-heating 
of unripe seed, or of seed stored in a moist condition, takes place from the 
effects of oxydases, or from micro-organisms, as in hay-, or from both 



1 "Gartenflora," Berlin, 1907, Part 2, p. 26. 

2 Miehe, H., tjber die Selbsterhitzung des Heues. Arb. d. Deutsch. Landw. Ges. 
Part 111, 1905, p. 76. 



6S3 

processes, we will consider here only the utilitarian value of the heated seed. 
We will mention, as example, an observation made by Bolley\ who found 
in overheated wheat, stack-burned as well as bin-burned, that the embryo 
was browned, or entirely killed. If the grains develop at all, the tips of the 
leaves usually die and the roots have no hair covering. The injured grains 
have lost their clear color and appear pale or browned. The testa is pale 
and wrinkled; the flavor of the grain, as a rule, is sweetish and the germin- 
ating power, even in grain which looks good, is weakened. 

The injury to the germinating power takes place so much the more 
rapidly the less ripened the seed was when stored or the less draughty the 
place of storage, since wind can dissipate the water vapor. According to 
Jodin's experiments- the use of a drying substance (slacked lime) has 
proved to be advantageous. 



1 Bolley, H. L., Conditions affecting- tlie value of wheat for seed. Agric. Exp. 
Sta. Nortii Dakota; cit. Zeitsclir. f. Pflanzenkrankh. 1894, p. 22. 

- Jodin, v., Sur la resistance des ^aines aux temperatures elevees. Compt. 
rend, 1899; cit. Bot. Jahresber. 1900. 11, p. 420. 



CHAPTER XIII. 



LACK OF LIGHT. 



Etiolation. 



The disease, which is produced by deficient illumination, or entire lack 
of light, is called etiolation (etiolement). The different stem members in 
the majority of green plants become uncommonly long and weak. Accord- 
ing to the variety to which they belong, the leaves, as well as the internodes 
of the stem, either become very long, slender and limp (the majority of 
monocotyledons), or develop only very slightly and remain, for their whole 
hfe, in a condition similar to that in the bud (most dicotyledons). 

A bleaching of the green parts of the plants, i. e., an arrested develop- 
ment, or decay of the existing chloroplasts, is connected with this change 
in form. We find exceptions only in the gymnosperms, of which the major- 
ity are unusually little susceptible to the removal of light. At any rate, 
according to Burgerstein^ the absorption of the endosperm becomes slower, 
the epinastic spread of the cotyledons less energetic and incomplete than in 
the light, but — with the exception of Gingko biloba and Ephedra — the seed- 
lings did turn green. Cycas and Zamia, on the other hand, cannot form 
any chlorophyll in complete darkness, even with a favorable temperature. 
Among conifers, the larches need the light most since they become only 
slightly green when it is excluded, while the Cupressineae become com- 
pletely green. 

The difference in the formation of the leaves of etiolated plants is 
explained by the fact that the leaf, for the most part, must nourish itself 
and that the cellulose material, which it needs for the new formation and 
maturing of the leaf cells, can be formed only by the action of the light on 
the very spot. If the nutriment is suppressed, the leaf cells, already formed 
in the bud, elongate with the absorption of water, on which account the 
leaf itself will become somewhat larger, but all further growth, depending 
on cell increase, will be impossible. The more the leaf, in its later enlarge- 
ment in the light, depends on cell increase, the smaller it remains when tlie 



1 Burg-erstein, A., tJber das Verhalten der Gymnospprmen-Keimlinge im Lichte 
und im Dunkeln. Just's bot. Jahresb. 1900, II, p. 250. 



655 

light is shut away. Further, it will develop so much the less, the fewer the 
cells originally formed as leaf primordia at the tip of the stem; a clasping 
leaf, on this account, will develop further than a whirl leaf can, because, 
in the primordia of the former, the whole circumference of the stem is 
active, while in those of the latter, the cells at the same height on the stem 
must be divided among as many leaves as the whirl numbers. A further 
point, which must be of influence on the development of the leaf in the 
dark, is the distance of the leaf primordia from the source of the reserve 
substances. Those produced first, and lying nearest a reserve substance 
store, remove more material from the supply and, on this account, become 
larger than those produced later and higher up on the etiolated stem. Thus 
the development of the etiolated leaf is dependent on the individual 
primordia and on the amount of nutrition to be found in its immediate 
proximity. 

The primordia of the monocotyledon leaves, in the majority of cases, 
are formed like a roll, surrounding the stem, below the vegetative cone and 
in the immediate proximity to reserve substance stores, when these are 
present, from w^hich the dissolved constructive material has to pass only a 
short distance through the shortened axis (grasses). 

Having discussed the etiolation phenomena of the leaf, the unusual 
elongation of the etiolated stem members remains to be explained. We will 
follow in this the statement made by Kraus\ As a rule, etiolated stems are 
thinner than normal ones, caused by a lesser number of cells, and this 
deficient activity in the cambium of the stem is explained by the assumption 
that some of the nutritive substances, worked up by the leaf, which pass 
over into the stem through the petiole, pass further in a radial direction and 
help to nourish the cambium of the internode of the stem. If this source of 
nutrition fails, i. e., the leaf, which in the dark remains in the form of a 
scale, is not in a position to obtain material for cell increase, the stem mem- 
ber remains as it is without any actually new cell formation. The thicken- 
ing of the cell walls is also suppressed. In normal stems the parenchyma 
cells of the bark and the prosenchyma cells of the wood become thickened 
during their growth in length. The pith cells, however, begin to grow 
thicker only when elongation is approximately at an end, i. e., at the latest 
moment, since they are only reached by the cellulose micella, wandering in 
a radial direction from the leaf into the interior of the stem, when it is no 
longer used to thicken the wood or bark cells. In etiolated stems, because 
of the lack of nutrition, the thickening of the cell is only indicated, so that 
it is almost lost in those which lie between the different vascular bundles 
and, in the normal condition, develop into wood cells. On this account, 
frequently no closed wood ring is found in the etiolated plants. The loss 
in thickness suffered by these cells is compensated for by their greater 
length, which exceeds that of the normal cell from two to four times. 



1 Kraus, C, tJber die Ursachen d. Formveranderung-en etiolierender Pflanzen. 
Pringsheim's Jahi-b. f. wiss. Bot., Vol. \"II, Part 1, 2, p. 209 ft. 



656 

This excessive length is explained by the modified tension conditions in the 
stem members. 

The bark, if loosened from the growing part of the stem, contracts ; 
the isolated pith body, on the other hand, becomes considerably longer. It 
is evident from this that, in the stem, the pith is really the elongating factor, 
while the rest of the tissue represents the restraining factor. Only when 
the stem is still very young can the pith satisfy the impulse for elongation 
because the surrounding tissues are still thin-walled and very easily 
stretched. They can, therefore, most easily follow passively the strain 
which the pith exercises. Gradually, however, the elasticity of the outer 
tissue Is entirely lost and the longer pith is now restrained by the thick- 
walled bark and wood elements. In the latter developmental stage, shortly 
before the stem member ceases growing, the differences in the tissue are 
equahzed, for now the pith cells grow broader rather than longer, as a result 
of the restraining influence of the bark layers and, in this form, become 
stable since the porous thickening layers are now formed in the cell wall. 

Therefore, the longer the bark elements remain elastic, so much the 
longer can the pith follow its impulse to elongate and draw the other tissues 
out with it. 

The etiolating plants often resemble juvenile organs and the condition 
of etiolation, up to a certain degree, can be designated as a permanent juven- 
ile form. 

After discussing the morphological changes, we have still to consider 
some metabolistic processes. First of all we will mention the investiga- 
tions of E. Schulze and N. Castoro^ on Lupinus albus. In etiolated seed- 
lings, the protein content decreases constantly, while asparagin increases ; 
tyrosin and leucin decrease. At any rate, seedlings grown in the light 
retain for a long time a high amount of asparagin but contain very little 
amino acid. 

Palladin's^ experiments make it evident that the decreased current of 
transpiration in etiolated plants causes a too slight absorption of mineral 
elements, especially calcium. A lack of calcium salts, however, even in 
leaves rich in proteins, prevents all further development. 

Wiesner^ has shown by numerous experiments that plants grown in 
the dark are less resistant to atmospheric influences. He found, for 
example, that seedlings, grown in the light, are much more resistant to the 
action of rain and water in any form, than seedlings developed in the dark. 

Observations made by Maige'* on Ampelopsis and Glechoma show how 
the material differences come to expression in growth. Diffused light 

1 Schulze, E.. u. Castoro, N., Beitrage zur Kenntnis der Zusammensetzung- und 
des Stoffwechels der Keimpflanzen. Zeitschr. f. phys. Chemie, Vol. XXXVIII. Cit. 
Botan. Centralbl. 1904, No. 47, p. 540. 

2 Palladin, W., Eiweissgehalt der griinen und etiolierten Blatter. Ber. d. 
Deutsch. Bot. Ges. Vol. IX, p. 194. — Ergrunen und "Wachstum der etiolierten 
Blatter. Ibid. p. 229, 

3 Wiesner J. Der Lichtgenuss der Pflanzen. Leipzig 1907, W. Engelmann. 
p. 260. ' ' '#i<Wr 

4 Maige, Influence de la lumiere, etc. Compt. rend. 1898, p. 420. Cit. Bot. 
Jahresber. 1898. I, p. 587. 



657 

furthers the formation of the leaf shoots and can, in fact, cause the trans- 
formation of an inflorescence bud into a cHmbing branch. Direct sunshine 
has an exactly opposite effect. 

Green's experiments^ are very important for pathology and especially 
for the point of view which we would represent, that a whole series of 
diseases is caused by a change in enzymatic functions. He confirms the 
observations of Brown and Morris that the supply of diastase in the foliage 
is diminished after a period of bright illumination. The ultra violet and 
adjoining visible rays are especially important in producing such an enzy- 
matic decrease. Such an enzymatic destruction by light may be compared 
with the well-known killing of bacteria by light. 

Shading. 

In agriculture, the injuries produced by direct etiolation are much less 
frequent and, on this account, less significant than the lower grade of occur- 
rences which arise from an insufficient supply of light; i. e., too strong 
shading, and make themselves felt in the decreased production of useful 
substances. Stebler and Volkart- have made measurements of the removal 
of light caused by different trees. With a clouded sky, they found a 
decrease of light from the pine of 50 per cent. ; from the birch, 56 per cent. ; 
from the cherry, 78 per cent. ; from the oak, pear and apple, 82 per cent. ; 
and from the beech, 95 per cent. 

Since each plant has its, definite need of light, cases also occur in which 
cultivation gives an excess of light, while the natural habitat would furnish 
the plant with only a subdued amount. This is found in many of our hop 
fields and in strawberry culture''. In such cases, shade causes an increased 
production but, in the majority, reduces the amount of dry substance and 
weakens the color of the foliage and blossoms. The question of shading 
may be of especial importance for our colonial plants. In Java, as well as 
in our East Africa colonies, coffee plantations suffer very frequently and 
Zimmerman* ascribes this to a lack of shade trees which would prevent 
over-production by the coffee trees; for example, in Usambara, this has 
already caused great injury. It is probable that the consequent lessened 
strength of illumination, besides the protection from the wind and decrease 
of temperature, especially favors the thriving of coffee. 

The decreased harvest from plants which need light, due to the influ- 
ence of the shade of trees, arises not only from the limited amount of light 
but also from the lesser warming of the soil. E. v. Oven's experiments^ 

1 Green, J. Reynolds. On the action of light on diastase. Phil. Trans, of the 
R. Soc. of T.ondon. Ser. B. Vol. 188; cit. Bot. Jahresber. 1897. I, p. 89. 

~ Stebler, F. G., u. Volkart, A., Der Einfluss der Beschattung- auf den Rasen. 
Landwirtseh. Jahrbiicher. d. Schweiz. Bern 1904; cit. Bot. Centralbl. 1908, Vol. 
101, p. 60. 

3 Taylor, O. M., and Clark, V. A.. An experiment in shading- strawberries. New 
York Agric. Exp. Sta. Geneva Bull. 246. 1904. 

4 Zimmerman, A., Einige Bemerkungen zu dem Aufsatze von Fr. Wohltmann, 
usw. Berichte liber Land- u. Forstwirtschaft In Deutsch-Ostafrika. Vol. I, Part 5, 
1903. 

5 V. Oven, iJber den Einfluss des Baumschattens auf den Ertrag" der Kartoffel- 
pflanze. Naturw. Zeitschr. f. Land- u Forstwirtschaft. 1904, p. 469. 



658 

show how great the differences can be. He found an average temperature of 
22.26 degrees C. at 9 A. M. on ten days in August, in soil on which the sun 
shone, but, under a cherry tree, a temperature of 19.06 degrees C. In 1884, 
Wollny^ had already measured the influence of soil shading due to weeds 
in a potato field and found, at a depth of 10 cm. in the soil, that the temper- 
ature averaged 2.6 degrees C. less than on a field cleared of weeds. 

Besides the temperature, the amount of water in the soil is of impor- 
tance. Gain's measurements^ show how much the soil moisture influences 
the size of the leaf. He reckoned the length of the organs set in a dry 
habitat at 100, the dimensions on damp soil for barley were 240 ; for poppies 
550; for potatoes 150. 

If the plants continue to have too little water, their maturing is natu- 
rally delayed ; their productivity is also considerably reduced. In this 
connection Bimer's experiments^ should be mentioned. He found that the 
ripening of potato plants was delayed 8 days in a soil with a 40 to 30 per 
cent, saturation capacity ; 18 days in a 30 to 10 per cent, saturation capacity 
in contrast to plants with an abundant soil moisture (80 per cent, saturation 
capacity). With the same high moisture content of the soil, WoUny har- 
vested 80 g. of tubers from pot plants, while he obtained only 39 g. with 
half the water content of the soil and only 19.5 g. with 20 per cent, satura- 
tion capacity. 

In growing herbaceous plants with shallow spreading roots, the yield is 
markedly decreased by the deeper lying tree roots. In v. Oven's investiga- 
tions, the water content under a cherry tree amounted to 20.24 per cent., in 
the unshaded vicinity, however, it amounted to 21.78 per cent. According 
to Wollny, 2.86 per cent, more water was withdrawn from a potato field by 
the weeds than by the potatoes alone. 

V, Oven describes the influence of shade on the plant itself, according 
to his own observations and those of other scientists. The stem members 
become longer; the leaves more slender and the ripening is retarded. The 
epidermis, the sheath of the vascular bundles, the walls of the ring ducts 
and medullary parenchyma are not so thick and the lignification is less. 

The cause of the lengthened period of growth of plants in the shade 
must be looked for in the lesser intensity of metabolism, which manifests 
itself in the weaker respiration, since, according to our experiments, the 
amount of assimilatory activity, under otherwise equal conditions, deter- 
mines the degree of transpiration, and this also explains the essentially lesser 
evaporation, and, on this account, the higher water content in shaded plants. 

Of the numerous experiments, which determine a reduction of the 
harvest due to shade and which v. Oven cites, in addition to his own, one 
by Wieske on a wheat field is of interest. The plants, which were shaded 
for the greater part of the day by fruit trees, gave a grain yield decreased 

1 Wollny, Forschungen auf dem Gebiete der Agrikulturphysik, Vol. VII, p. 349. 

2 Bot. Centralbl., Beihefte. Vol. IV, p. 418. 

3 Bimer in Biedermann's Centralbl. 1881, p. 154. 



659 

about 30 per cent., and a straw yield about 32 per cent, less than the un- 
shaded plants in the same fields. 

The results which Pagnoul^ obtained are especially noteworthy. In 
experiments with sugar beets, he found a strong falling off in sugar content 
with an increase of the leaf substance per gram of root body and, for pota- 
toes, a decreased tuber yield with a significant falling off of dry substance. 
Besides this, however, he proved that the nitrate content for beets and 
potatoes, grown under blackened glass, was more 'than ten times as great in 
the leaves and roots as in plants grown in the sunshine. Therefore, the 
physiological activity was changed in the shade since the nitrates were not 
sufficiently used up. 

Some of v. Oven's experiments took up the measurement of the inten- 
sity of the light which remained after the sun's rays had passed through a 
tree crown. It was shown by the Bunsen-Roscoe method, that the propor- 
tion of full daylight to the amount of light under fruit trees was about i to 
0.3. The shade of apple trees reduces the intensity of the light, on an 
average, from i to 0.234; the shade of pear trees from i to 0.233; that of 
cherry trees from i to 0.345. 

For practical purposes, the lesson may be drawn from existing obser- 
vations that the cultivation of fruit trees between field plantations, so widely 
recommended, is unprofitable for northern regions. For southern countries, 
in which an excess of light and heat may at times injure the plants, the 
method will be advantageous. We find this theory confirmed by the fact 
that in Italy the fields are divided by rows of mulberry and olive trees, as 
well as by grapevines. According to Linsbauer- the cultivation of grapes 
in Italy (on pergolas) and in Austria (on low stakes) has been determined 
by adaptation to the light conditions. In southern regions, thedonger dura- 
tion of the sunshine permits the shading method of growth on arbors, while, 
in northern countries, the shorter period of sunshine must be fully used. 

Like Frank-Schwarz, we reproduce illustrations of beech leaves from 
Stahl's well-known studies on the structure of shade leaves. In Fig. 152 
may be seen a beech leaf grown in the sun, in Fig. 153, one grown in half 
shade; and in Fig. 154, another matured in strong shadow. We see from 
these how the leaf decreases in size with deficient illumination. The pali- 
sade cells (pp) are formed in a less characteristic way, the spongy paren- 
chyma (schp) becomes especially reduced and the vascular bundle cords 
weaker ; a more feeble bud development is coordinated with the lesser leaf 
development. 

The formation of the tissue, especially the differentiation in the paren- 
chyma tissue^, depends upon the light intensity in the spring. Hesselman"* 



1 Annales agronomiques. Vol. "VII, 1891; cit. v. Oven. 

2 Wiesner, Lichtgenuss der Pflanzen. 1907. 

3 MacDougal, D. F., The Influence of Light and Darkness, etc.; cit. Bot. 
Centralbl. 1903. Vol. XCII, p. 296. 

4 Hesselmann, H., Zur Kenntnis des Pflanzenlebens schwedischer Laubwiesen. 
Beih. Bot. Centralbl. Vol. 17, 1904, p. 311. 



66o 



found that the plants, completing their development in a constantly reduced, 
but not especially small amount of light, show a much scantier formation of 
the assimilatory tissue than those specimens which have a good deal of light 
in the spring but are strongly shaded in summer. With an equal amount 
of leaf surface, plants grown in the sun, with their matured palisade paren- 
chyma, transpire considerably more strongly than those grown in the shade\ 
According to Ricome"-, the palisade cells are said to be taller but narrower, 
the vascular bundles more abundant in the petioles. The same difference is 
found between specimens grown out of doors and in conservatories^. 

Investigations made by Count zu Leiningen* give us a satisfactory in- 
sight into the amount of work performed by light and shade leaves. He 




Fig. 152. Cross-section through a beech 

leaf matured in the sun. (After 

Stahl.) 



Fig. 153. Cross-section through 

a beech leaf from a half shaded 

position. (After Stahl.) 




Fig 154. Cross-section through a beech leaf from a very shady place. 

(After Stahl.) 

fip palisade parenchyma, sc/i spongy parenchyma. 



found in the beech, reckoned on the same amount of leaf surface, a con- 
siderably smaller content in pure ash (with the exception of silicic acid) in 
sun leaves than in shade leaves; the nitrogen content was corresponding. 
We explain this condition of affairs as follows : — the root system provides 
the leaves with equal amounts of mineral substances ; it now depends upon 



1 Bergen, J., Transpiration of sun leaves and shade leaves of Olea europaea 
and other Orval-leaved evergreens. Bot. Gaz. Vol. 38, 1904, p. 285. 

2 Ricome, R., Action de la lumiere sur des plantes etiolees. Rev. gen. de Bot. 
1902, t. XIV, p. 26. ^ „ . ^ ^, 

3 Ktister Review of "Bedelian, Influence de la culture en serre, etc., m JrLoil- 
rung's Jahresber. iiber Leistungen auf d. Geb. der Pflanzenkrank. Vol. VII, 1905, 
p. 7. (Further notes on Sun and Shade Leaves, cf. Kiister, E., Pathologische Pflan- 
zenanatomie 1903, p. 24, etc.) , „ , -x. x 

4 Leiningen, Wilhelm, Graf zu, Licht. und Schattenblatter der Buche. ISaturM, 
Zeitschr. f. Land- u. Forstwirtsch, 1905, III Year, Part 5. 



66i 

how these are made use of. The more vigorously a plant grows, the more 
organic substances it produces per gram ash. Therefore, a lesser assimil- 
atory activity must be concluded each time, if the analysis proves a high 
ash content in proportion to the dry substances. In the present case, the 
scanty amount of light is the factor reducing production. 

Sensitiveness to shade is, at any rate, connected with a definite limit of 
value for each plant variety, but, as in all factors of growth, these values 
can shift individually to a certain degree, so that, in the same species, there 
may be races very sensitive to shade in which, in Nordhausen's^ opinion, 
certain reduction phenomena become herditary. 

Each leaf in the plant has its special sensitiveness to shade, according 
to the light conditions under which it was produced, and its position on the 
axis. The shade produced by leaves higher up is the most important. The 
amount of assimilation and respiration, as well as of transpiration, is deter- 
mined by this. In Griffon's experiments^, for example, it was found that 
a leaf, as thick as that of Primus Laurocerasus isnot able, in direct sunlight, 
to completely prevent the carbon dioxid decomposition in the leaf of 
Ligustrum ovalifolium. Under two such leaves, however, the development 
of carbon dioxid took place. Under such conditions, therefore, assimilation 
was so reduced that respiration exceeded it. 

It naturall}^ depends also upon what color the shaded plant parts are, 
i. e., which light colors can still pass through them. 

According to Teodoresco^ the leaf tissues develop most poorly in green 
light ; they are found to be better in red light ; the best development, how- 
ever, is found in blue light, and, therefore, the greatest enlargement. The 
chlorophyll grains are also smaller in green light, less numerous and not so 
regularly distributed as in red and blue light. 

The product of the activity of the chloroplasts, corresponding to their 
development, is proved especially favorable in the most strongly refrangible 
rays. Palladin'' exposed etiolated cotyledons of Vicia in sugar solutions to 
white and colored light and found that the assimilation of the sugar, as well 
as the formation of active proteids, took place most vigorously in the more 
strongly refrangible light rays and, therefore, respiration was more intensive. 

If the leaf, because of a scanty light supply, cannot work any longer, 
it falls off, just as under the action of all other factors which suppress its 
assimilatory activity^. This explains the regular "summer leaf fall," which, 
naturally, is dift'erent from leaf fall due to heat. Wiesner*^ explains the 



1 Noixlhausen, M., tJber Sonnen und Schattenblatter. Ber. d Deutsch Bot 
Ges. Vol. XXI, 1903, p. 30. 

2 Griffon, Ed., L'assimilation chlorophyllienne dans la lumiere solaire qui a 
traverse des feuilles. Compt. rend. CXXIX, Paris 1899, p. 1276. 

3 Teodoresco, E., Influence des differentes radiations, etc.; cit. Bot. Jahresber. 
27. Jahrg-. 1901. Part It, p. 133. 

•1 Palladin, W., Influence de la lumiere, etc.; cit. Bot. Jahresber. Jahrg. 1899, 
II, p. 134. 

5 Vochting-, H., tJber die Abhangigkeit des Laubfalls von seiner Assimilations- 
tatigkeit. Bot. Zeit. 1891, Nos. 8 and 9. 

6 Wiesner, Jul., tJber Laubfall infolge Sinkens des absoluten Lichtgenusses 
(Sommerlaubfall). Ber. d. Deutsch. Bot. Ges. Jahrg. XII, Part 1, 1904, p. 64. 



662 

"summer leaf fall" in that the lowering of the daily light intensity, follow- 
ing the beginning of summer, brings about a lowering of the (absolute) 
amount of light, for the plant concerned, below the minimum, whereby an 
immediate loosening of the leaves is caused. 

The amount of bloom for each plant depends, of course, upon the 
abundance of the carbon assimilation, hence shaded specimens bloom less. 
Exclusively diffuse light delays the time of blooming and can prevent the 
complete ripening of the fruit, so that the seed will atrophy \ 

There are cases where plants, with a previously abundant assimilation, 
are placed in the shade before their blossoms develop. In the dark, the 
blossoms appear later, as a rule. Their color is paler and at times white; 
their size and amount of substance less and the peduncles not infrequently 
longer-. If however, the leaves are left in the light and only the branches, 
bearing the blossom buds, are darkened, then, according to Kraus^ the 
flowers, with a few exceptions, develop completely. 

We have considered in the previous section the thin-walled condition of 
the cell elements in etiolated plants. 

The Lodging of Grain. 

The lodging of the stalks for a long period effects a loss in quantity 
and quality of the harvest. It is the more dangerous the more the bending 
of the stalk approaches actual breaking over. Investigators were inclined 
earlier to assume one single cause for this lodging until later observations 
determined that very different factors can come into effect and that, accord- 
ing to the causes, the breaking over of the stalk takes place sometimes at 
the base in the soil, sometimes close above this point, or higher on the stalk. 

Thus we know now that frost injuries often produce weakening of the 
stalks which without, or (usually) with the later co-operation of some fun- 
gus, initiates their falling over. Further, eating by insects, breaking from 
the wind, hail, long continued rainfall, not infrequently cause a direct falling 
of the stalks. 

While, however, the majority of the factors named cause a lodging of 
the grain in spots so that stalks remain standing upright between these 
places, the actual lodging most feared by the agriculturalist is the one 
occurring in continuous areas, due to weak development of the bases of 
the stalks. 

L. Koch*, who has definitely shown by experiments that this results 
from a lack of light, produced artificially the phenomena of lodging by 
shading the stalks. The experiments made earlier by Gronemeyer^ were 



1 Passerini, N., Sopra vegetazione di alcune piante alia luce solare diretta e 
diffusa, cf. Just's Jahresber. 1902, II, p. 628. 

2 Beulayg-ue, Einfluss der Dunkelheit auf die Entwicklung der Bliiten. Bieder- 
mann's Centralbl. 1902, p. 102. 

3 Kraus, tjber die Ursachen der Formveranderungen etiolierender Pflanzen. 
Pringsheim's Jahrb. f. wiss. Bot., Vol. VII, p. 209. 

4 Koch, Ludwig, Abnorme Anderungen wachsender Pflanzenorgane durch 
Beschattung. 

5 Gronemeyer in Agronom. Zeit. 1867, No. 34. 



663 

thus confirmed. The weakness of the stalks, which conditions the falHng 
over in lodging is found actually in the lower stem members and the second 
intemode (reckoned from the base of the stalk) is the one usually bent over. 

To be sure, the first, lowest stem member is also weak, but, as a rule, it 
is too short to bend over ; on the other hand, the second is the most elongated 
and the least thickened. The cells of this internode in lodged grain show a 
considerable over-elongation and scanty thickening in proportion to the 
corresponding cells of the normal stem. This deficient thickening is espe- 
cially noticeable in those cells which, in the blade, fill the space between the 
outer membrane and the vascular bundle sheath, and actually conditions the 
firmness of the stalk. 

Lodging of grain, therefore, is produced when the lower internodes of 
closely planted grain are insufficiently lighted. Too great shading also acts 
disadvantageoiisly in the very early developmental stages of the plant by the 
over-elongation of the cells and the scanty thickening of the walls, which, 
as said above, takes place usually in the second internode from the bottom. 
This bad condition will occur more strongly in the places in the internodes 
where the leaf sheath surrounds the stalk most closely. This takes place 
near the base of the stem and the phenomena of etiolation are found most 
clearly and intensively here. 

Formerly a lack of silicic acid was assumed as one reason for the 
lodging of grain. This may now be explained as erroneous, since it has 
been shown by water cultures of grain plants, that minimal amounts of 
siHcic acid are sufficient to produce a normal plant and since analyses of 
lodged grain, compared with grain which had not lodged, have shown but 
little difference in silicic acid content. In normal plants also, as Pierre has 
shown for wheat and Arendt for oats, the lowest internodes of the stalk 
are the poorest in silicic acid, of which the greatest quantity in any case is 
found in the leaves. These can be 7 to 18 times as rich in silicic acid as 
the lower stem members. 

Connected with the lack of light is the second point, given as a cause 
for lodging, namely, that the disease may be traced to an excessive supply 
of nitrogen in the soil. At any rate, this is one cause inasmuch as a too 
luxuriant development of the leaf apparatus is thus produced, essentiallv 
increasing the shading. Such a cause is given, however, by every circum- 
stance which conditions a too thick stand from the seed, i. e., for example, 
too abundant seeding, too abundant water supply, etc. 

Experiments made by Ritthausen and Pott^ show the change in the 
maturing of fruit due to different nitrogen fertilizers and the tendency of 
the plant to lodge. While the grains of summer wheat are well matured with 
an abundant supply of nitrogen but remain small and glassy like the seed, the 
grains from plots not fertilized with nitrogen, lodge after less heavy rain- 
storms. Kreusler and Kern confirmed the above statements". We may 



1 Landwirtsch. Versuchsstationen 1873, p. 384. 

2 Centralbl. f. Agrikulturchemie 1876, I, p. 401. 



664 

have in pure phosphoric acid fertiUzation a means of decreasing the dangers 
of a too large supply of nitrogen. At least, the results obtained by the 
above-named authors v^uth wheat and barley showed that a fertilization with 
phosphoric acid alone (Baker guano with 18.97 per cent, soluble Pg O..; 
resulted in a reduction of the nitrogen content of the grain. 

But, aside from the composition of the grain, which is changed by an 
increased nitrogen supply, the whole amount of the harvest must be taken 
into consideration, which had suffered not a little from a too luxuriant and, 
therefore, too thick and dark a growth of the plant. Experiments based 
mostly on the conditions occurring in practice, since they show the influence 
of shading from the sides, have been cited by Fittbogen\ Under otherwise 
perfectly similar nutritive conditions, he shaded barley plants by means of 
a cylinder of rye stalks, fastened side by side and placed around the barley 
plants, and raised it in proportion to the growth in height of the experi- 
mental pl^nt, which was constantly illuminated at the tip. The plants, 
therefore, had light for production but still in insufficient amounts. On 
this account, they produced only about two-thirds as much dry substance as 
plants illuminated on all sides, in spite of the 4 to 6 weeks longer growth 
which were needed for complete ripening. The dry substance, however, 
was also distributed much less favorably in the different harvest products. 
While, with a normal illumination, 47 per cent, of the dry substance in 
summer barley, as a whole, was found in the grain, and 53 per cent, in the 
straw and chaff, from shaded plants, only 39 per cent, of grain was har- 
vested for 61 per cent, of straw and chaff', and the kernels were also poorer 
in quality. In regard to the water used, it was found that plants shaded on 
the sides, in spite of the at least 6 weeks longer growing time, had used only 
one-tenth more water in the hottest months (July and August). Therefore, 
in the same unit of time they absolutely transpired considerably less than 
the normally illuminated specimens, corresponding to the lesser production 
of dry substances. On the other hand, the plant will have evaporated rela- 
tively a great deal of water for we find, in shaded plants, that more than 
500 g. of water were used per gram of dry substance, while normally lighted 
specimens have respired only something over 300 g. for the same amount of 
dry substance. Therefore, we find, in this vegetative factor, the same effect 
on transpiration as in others (soil solutions, carbon dioxid content in the 
air, etc.) A supply of one vegetative factor kept beloiv the optimum, in- 
creases the relative use of water per gram dry substance produced. 

The loss due to lodging will be decreased in many cases by the fact 
that grain possesses the ability to right itself. The process of righting 
consists in the ability of the nodes to show phenomena of growth at a time 
when the internodes have already lignified. According to de Vries' expla- 
nation'-, a new formation of osmotically effective substances takes place in 



1 Vortrag aus clem Klub der Landwirte am 14. Dez. 1875. 

2 De Vries, tJber die Aufrichtung des gelag-erten Getreides. Landwirtschaftl. 
Jahrbucher von Thiel. IX, 1880, Part 3. 



665 

the parenchyma cells of the under half of the node, which carries out the 
bending, under the force of gravity, because the stalk with its node, is bent 
toward the horizontal. These parenchyma cells attract water. 

However, supported by the investigations of G. Kraus^, we would like 
to assume that no considerable formation of osmotically effective substances 
(acids) takes place, but rather a longer retention of such substances on the 
convex side, as a result of a decreased oxidation of the organic acids. At 
least Kraus proves that as much acid is present on the convex as on the 
concave side in the occurrence of geotrophic and heliotrophic bending. 

The only actually successful precaution lies in thinner seeding, the 
quantity of which must be modified according to the consistency of the soil. 
On sandy soils the seeding must be thicker than on loamy soils, and thicker 
with a poorer fertilization than with an abundant supply of nitrogen. 
Planting with the drill is found to be the most useful because the best dis- 
tributed stand of plants is obtained thereby. 

If, however, the seeding has already taken place and a close stand, 
luxurious development, and moist weather give rise to a fear of a subsequent 
lodging, the attempt should be made to remove a part of the leaf apparatus 
by strong harrowing, rolling, or prudent mowing and uprooting, in order to 
provide a sufficient access of light. 

In regard to cultural regulations, we must refer to the recently pub- 
lished, very thorough work of C. Kraus", based on, experimental studies, 
because the precautionary regulations, according to the different causes of 
lodging here mentioned, must also dift'er greatly. On general principles, it 
is not only a question of growing strong plants as resistant as possible to 
disturbances in equilibrium, but also to take pains that the plants, me- 
chanically well developed above and below the soil, find the indispensable 
support within the soil of a properly developed root system. The task of 
breeding now follows these two directions. Even the weather at the time 
of seeding acts determinatively for the position of nodes, regulating essen- 
tially the anchorage of the plant in the soil. According to Schellenberg^, 
the node lies higher if the seed develops in cloudy weather. It is, therefore, 
more advantageous (even for winter grain) when the seeds sprout in clear 
weather. 

In weak stemmed plants, inclined to lodge, there occurs also at tiroes 
a decay of the parts entirely removed from the light, which causes consid- 
erable loss in the lodging of fodder peas. The sowing of some horsetooth 
maise with these is recommended as a precaution. The peas can climb up 
the stems of the maiSe and its leaves also furnish good fodder. 

The sowing of gold of pleasure (Camelina sativa) possibly 6 liters per 
hectare, is also recommended to prevent the lodging of peas, sweet peas, 
etc. This plant, which is perfectly hardy, ripens about the same time as 



1 Sitzungber. d. naturf. Ges. zu Halle 1880; cit. Bot. Centralbl. 1882, I, p. 107. 

2 Kraus, C, Die Lagerung- der Getreide. Stuttgart 1908, Eugen Ulmer. 

3 Schellenberg, H. C, Untersuchungen iiber die Lage des Bestockungsknotens 
beim Getreide. Forsch. auf d. Gebiete d. Landwirtsch. Frauenfeld 1902. 



666 

peas and the kernels may be easily separated from the peas by sifting, while 
the grain, generally grown with peas (summer rye and oats), is sifted out 
with much more trouble and exhausts the soil more for the following winter 
crop. ' 

Here also, as in grain, breeders are now directing their attention to 
resistance to lodging. The Bulletins^ published by the German Agricul- 
tural Society have proved to be most advantageous in this direction. They 
contain the latest results of cultural experiments with the different varieties 
of our cultivated plants. 

Lack of Light as Predisposition to Disease. 

When it comes to the attacks of parasites, the mechanical resistance of 
the membranes of etiolated plants will be less. However, the atmospheric 
influences become weaker and their fluctuations, reaching directly the cyto- 
plasmatic cell body, can disturb its functions even if the etiolated plant 
should work in the same way and with the same energy as one which has 
sufficient light. 

The last is, however, by no means the case. 

The first indication of a change in function is found in the moving of 
the chlorophyll grains toward the side walls, in the dark. At the same time 
another significant change begins, viz., the closing of the stomata. Accord- 
ing to Schwendener^ this phenomenon, already observed in complete dark- 
ness, also sets in with a sudden decrease in the intensity of illumination. It 
is possibly not a result of the lowering of the temperature connected with 
the decrease of fight, for an increase in temperature within the usual fluc- 
tuations causes no opening of this apparatus. Connected with this also is 
the fact that a longer suppression, or reduction of the exchange of gases, 
can bring about changes in the cell contents, due to a lack of oxygen, that is, 
for example, a tendency to the formation of alcohol. These disturbances 
will occur so much the more easily, the more intense the capacity for growth 
and the greater the need for ventilation. Therefore, very young organs will 
feel this, while old leaves, grown for many years, with a lesser need of light, 
endure longer limitation in the exchange of gases. Nature indicates this 
also by the wall thickening of the guard cells, increased with advancing age, 
which, according to Schwendener, is so strong at times that no further 
opening of the stomata can be possible. 

In regard to lessened transpiration, I found in young seedlings of 
Phaseolus, dependent upon their cotyledons, such a difl^erence between 
etiolated and normal plants that the former, on an average, transpired in 
the same period of time, 0.21 g. per sq. cm. leaf surface; the latter, 0.29 g.^ 
The production of dry substance in a plant, under otherwise equal condi- 



1 Mittel. der Saatzuchtstelle iiber wichtige Sortenversuche 1905-1907 usw. 

2 Schwendener, tjber Bau und Mechanik der Spaltoffnungen. Monatsber. d. Kg-I. 
Akad. d. Wiss. zu Berlin, July, 1881; cit. Bot. Zeit. 1882, p. 234. 

3 Sorauer, Studien iiber Verdunstung. Aus WoUny's "Forschung-en auf dem 
Gebiete der Agrikulturphysik." Vol. I, Part 4-5, p. 116. 



667 

tions, parallels the transpiration. Investigation showed that not only the 
absolute production of the young plants was essentially more energetic in 
the light, but that also a square centimeter of leaf surface developed a 
greater amount of substances. A weakening of the light, by means of col- 
ored media, through which the rays must pass, acts similarly to the removal 
of light by placing it in the dark. In yellow light, assimilation and transpi- 
ration are more energetic than in blue light; at least the majority of experi- 
ments favor this^. 

The energy of production of plants and also the mode change with the 
decrease of light and this change is expressed, not only in the metamorphic, 
but also in the metabolic structure. 

The well-known experiment of covering leaves in the light with a 
stencil pattern, which leaves free some rather larger surface figures, remov- 
ing the green from these leaves after som.e days by means of alcohol, and 
then wetting them with iodine solution, is a simple illustration of the action 
of light. All parts of the leaf, which have been exposed to the light, look 
blue because of the action on the starch which had been formed in the light. 
This experiment is of interest inasmuch as it shows how locally limited the 
action of light is. Only the part which had been illuminated formed starch 
and no starch passed over into the darkened, adjacent part. The most 
important thing, according to this, is that the green parts of the plant must 
themselves work over their constructive materials if they should continue 
to hve. 

It has been mentioned already that the mobilized reserve substances 
pass into the young, entirely darkened shoots a certain distance from the 
tubers and seeds. If the distance is too great, however, the shoots finally 
die from starvation. They breathe up more respiratory material than thev 
receive in the form of sugar, etc. Some of Miiller-Thurgau's- experiments 
show, for example, that the starch, when dissolved, passes over into sugar, 
which is used up partly for construction and partly in respiration. Grape 
leaves, which contain 2 per cent, sugar and as much starch, were cut off and 
their petioles put in water. The contairier was set in a room at zero de- 
grees. Nine days later all trace of the starch had disappeared. Since the 
respiration of the grapevine, however, at zero degrees is very slight, the 
sugar, produced by the solution of the starch m the dark, cannot have been 
used up in respiration and must, accordingly, have accumulated in the leaf. 
As a fact, investigation shows 4 per cent, sugar in the leaves. 

Thus, placing in the dark wdll promote the formation of sugar in the 
organs as against the formation of starch. If, as is frequently the case in 
growing plants out of doors, an actual temperature decrease takes place 
with the decrease in light, it means a blocking of sugar in the assimilator}' 
tissues. 



1 Compare Hellriegel, Beitrag-e, p. 378. Nobbe, Versuchsstationen XXVI, p. 354. 
Flahault, Bot. Centralbl. 1880, p. 932. Deherain, Bot. Zeit. 1873, p. 494^ 

2 Miiller-Thurgau, tJber den Einfluss der Belaubung auf das Reifen der Trau- 
ben. Weinbaukongress zu Dilrkheim a. d. H. 1882. 



66S 

Anyone who has cultivated fungi in nutrient solutions knows, however, 
how favorably a supply of sugar acts on the development of many parasitic 
fungi. 

Cloudy, cool days, therefore, not only weaken the assimilation in the 
green parts of the plants but, at the same time, by reducing the respiratory 
processes, bring about an accumulation of sugar in the leaf cells and, there- 
fore, make possible the production of a more favorable substratum for 
parasites. 

The acid content of the various plant parts is also very different in 
the dark from that found when the organ is favorably illuminated. 

The observation, that many plants (Crassulaceae) taste sour at night^ 
but not noticeably so during the day- is very odd. In etiolated plants, Wies- 
ner could recognize an abundance of organic acids^ in the leaves of many 
monocotyledons, and later De Vries observed* that the stems of etiolated 
dicotyledons are strongly acid. When illuminated, the rich sugar content 
disappears. This has been, at least, especially proved for the Crassulaceae, 
in which, in the night, De Vries could determine a rich acid formation only 
when the plants had been abundantly lighted during the day, but, if the 
supply of light was limited to a few hours, the acid content in the night was 
correspondingly less. 

An increase of warmth increases also the decomposition of the acids in 
the dark. Cooler nights lead to the storage of acid. 

De Vries has proved this directly by experiments^. It is evident, how- 
ever, from the fact that the loss of acid becomes less with each successive 
day of shading, that the disappearance of the acids is connected with the 
supply of material for the formation of acid which has been worked over 
in the light. 

Plants, therefore, constantly produce acids and the more energetically 
the stronger growing the organs are. With light, the acids are oxidized as 
fast as they are produced ; in the dark, they are stored up. On this account, 
etiolated plants are relatively rich in acids. The suppression of the inflor- 
escences increases the content of free acids in the leaf. The acid content 
in the roots is also subjected to great fluctuations and, according to Chara- 
bof^, in plants cultivated in the shade it is, in fact, larger than in the leaves. 
In general, this acid content is greater in etiolated plants. 

This accumulation of acids in and of itself can offer those fungi, which 
decompose acids, the possibility of colonization and luxuriant development ; 

1 Heyne und Link in Jahrbuch der Gewachskunde von Sprengel, Schrader und 
Link, 1819, p. 70-73. 

2 Ad. Mayer, tJber Sauerstoffausscheidung usw. Verhandl. d. Heidelberger 
naturf. Gesellsch. 4-8, 1875. Landwirtsch. Versuchsstat. 1875, Vol. XVIII, p. 410, 
Vol. XXI, p. 277. 

3 Wiesner, Sitzungsber. d. K. K. Akad. d. "Wissensch. I, April, 1874, Vol. 69; 
cit. Bot. Zeit. 1874, p. 116. 

4 De Vries, tJber die Bedeutung der Pflanzensauren fiir den Turgor der Zellen. 
Bot. Zeit. 1878, p. 852. tJber die periodische Saurebildung der Fettpflanzen. Bot. 
Zeit. 1884, Nos. 22 and 23. 

5 Bot. Zeit. 1884, p. 340. 

6 Charabot, E., et Herbert, A., Recherches sur I'acidite vegetale. Compt. rend. 
1904, CXXXVIII, p. 1714. 



669 

however, an excessive increase of turgidity in the tissue can be ascribed to 
this since, according tolDe Vries, it is especially the plant acids which condi- 
tion the turgidity of the cells. 

The experiments of Viala and Pacottet^ on hlack rot (Guignardia 
Bidzvellii) show how very determinative this acid content can often be. 
Infection experiments in young berries are successful only so long as the 
acid content exceeds the sugar content. Not only the content in organic 
acids is increased but also the indifferent ash material is changed by the 
changed absorption of nutrition. This is shown by Andre's experiments- 
He tried to excite etiolated plants to unusual activity 'by increasing the tem- 
perature (30 degrees), but found only an unusual increase in the absorption 
of silicic acid, wuth an exclusion of other mineral elements. 

The decomposition and counter building of the proteins in the plant 
celP also stand in the closest connection with the above described processes 
of the formation and oxidation of the carbohydrates. 

In the germination and sprouting of buds on branches, roots and tubers, 
we find products of the decomposition of proteins which are similar to those 
of artificial protein decomposition, i. e., asparagin, glutamin, leucin, tyrosin, 
occur in very large amounts. According to Borodin's investigations* these 
amido compounds occur more abundantly, the fewer the elements present 
which are free from nitrogen (especially the grape sugar) and which can 
be used for the breaking down of the proteins. 

Since in etiolated plants, as well as in others grown in the light but in 
air free from carbon dioxid, the new production of carbohydrates is sup- 
pressed and since these are used up by day in respiration, an accumulation 
of asparagin will take place. Among the more recent observers, we will 
mention Zaleski (cf. next page) v/ho found an increase of asparagin in 
seedlings of Allium Cepa. The above mentioned work by Schulze and 
Castoro'^ should be especially considered, from which it is seen that, for 
example, in etiolated seedlings of Lupinus Albus the content in protein 
substances decreases ; that in aspargin constantly increases. Tyrosin and 
leucin decrease. 

As a matter of fact, E. Schulze found more than half of the whole 
nitrogen content in 20 day old etiolated lupin seedlings in the form of 
asparagin". If now the nitrogen free part of the protein molecule is used 
up in respiration and no new elements, lacking nitrogen, are present to 
reconstruct normal protein in the protoplasm, the cell will undergo the most 



1 Viala, p., et Pacottet, P., Sur le developpement du Black Rot. Compt. rend. 
1904. CXXXIX, p. 152. 

2 Andre, G., Wirkung: der Temperatur auf die Absorption der Mineralstoffe bei 
etiolierten Pflanzen. Compt. rend. 1902; cit. Biedermann's Centralbl, f. Agrikul- 
turchemie 1903, Part 2. 

3 Pfeffer in Jahrb. f. wissensch. Bot. 1872, Vol. 8, p. 548. Tag-ebl. d. Naturf. 
Vers. z. "Wiesbaden. 

4 Bot. Zeit. 1878, p. 802 ff. 

5 Schulze, E., und Castoro, N., Beitrage zur Kenntnis der Zusammensetzung u. 
des StofTwechsels der Keimpflanzen; cit. Bot. Centralbl. 1904, Vol. XCVI, p. 540. 

6 Schulze, E., tjber den Eiweissumsatz im Pflanzenorganismus. Landwirtsch. 
Jahrbucher. 1880, p. 1-60. 



670 

extensive disturbances. It Is probable that a further decomposition will 
introduce phenomena of decay which produce the best nutrient substrata for 
parasites and saphrophytes. The asparagin is worked up well by the fungi 
in the presence of sugar. VogeP found in the germination of moistened 
cress seed that hydrogen sulfid was produced in the dark, while, in check 
experiments, in lighted places, the lead paper showed practically no change. 

A diflferent process may prevail in the leaf parenchyma from that in 
the leaf veins. In young Dahlia plants Borodin- proved the presence of 
saltpetre in the veins and in the petioles, but large amounts of tyrosin and 
no saltpetre in the leaf parenchyma. Here the tyrosin may well be no 
analytic product *but rather a synthetic one; for if the young shoots of 
dahlias become etiolated, no tyrosin is formed, but asparagin, which does 
not appear when the plants are grown in the light. 

At times, at any rate, an increase in proteins is found in the dark but it 
is then caused by the verv^ abundant carbohydrates at the plant's disposal in 
the stores of reserve substances, as Iwanoff^ has shown, for example, for 
Allium Cepa. If carbohydrates are present, the leaves, even in the dark, 
can change the nitrate nitrogen into protein nitrogen, as Zaleski* found in 
the leaves of Helianthus, which had been placed in a nutrient solution con- 
taining nitrates and sugar; 

We have stated here simply a series of facts which show the natural 
changes in the plant body due to a lack of light. These explain sufficiently 
the decreased power of resistance of the shaded plant parts through atmos- 
pheric influence, as well as parasitic attacks. 



1 Vogel, Ein auffalliger Unterschied zwischen Keimen am Tagreslicht und im 
Dunkeln; cit. Bot. Jahresber. 1877, p. 675. 

2 Sitszungsber. d. Bot. Sekt Petersburg. Naturf. Ges. 1881; cit. Botan. Zeit. 
1882; p. 589. 

3 Iwanoff, M., Versuche iiber die Frage, ob in den Pflanzen bei Lichtabschluss 
Eiweissstoffe sich bilden. Landw. Versuchsstationen 1901, p. 78. 

4 Zaleski, W., Die Bedingungen der Eiweissbildung in den Pflanzen. Charkow 
1900 (Russian) ; cit. Bot. Centralbl. 1901, Vol. 87, p. 277. 



CHAPTER XIV. 



EXCESS OF LIGHT. 



According- to the discoveries, already made in great numbers, on the 
influence of heat on the different vegetable processes, it must be supposed, 
from the outset, that not only does a minimal limit exist for the action of 
light, but that also a special degree of illumination exists in each plant for 
each process and for each combination of the vegetative factors, which can 
be termed the optimum. The exceeding of this degree introduces a retro- 
gression in production. In fact, the observation has already been made for 
a number of plants that, if the light is increased above a certain amount, 
the assimilation, perceptible in the elimination of oxygen, does not increase, 
but remains stationary^, or indeed may decrease-. A normal carbon dioxid 
content in the air is presupposed in this, for even when the air contains too 
large an amount of this element, the elimination of oxygen retrogresses, as 
has been proved already by Boussingault and, later, by Pfeffer^. An 
optimum illumination may be seen in the appearance of the plant since this 
loses its deeper green color, with a considerable increase in the intensity of 
light above the optimum ; then it assumes a yellowish color. 

That the dark green leaves of camellias show a yellowed condition, 
when moved from the conservatory into sunny places out of doors, is well 
known. The camellia is a Japanese plant which grov/s under trees. It is 
content with small quantities of light and, with the strong rays of our 
summer sun, soon loses more chlorophyll through oxidation than can be 
formed by the process of reduction. The breaking down of the chlorophyll 
by the taking up of oxygen (taking place also in the dark in the presence of 
bodies which easily take oxygen from the air and form ozone. Turpentine 
oil) is known to be connected with different groups of rays. According to 
Wiesner, the yellow rays, and the green and orange ones on both sides of 
them, show the greatest energy in the breaking down of the chlorophyll in 
the light. 

Another example of yellow leaves with a high intensity of light is 
offered by some varieties of coleus with yellow variegated leaves. These 

1 Reinke, K, Untersuchung-en iiber die Einwirkung-en des Lichtes auf die Sauer- 
stoffausscheidung der Pflanzen. Bot. Zeit. 1883, No. 42 ff. 

2 Famintzin, EfCet de I'intensite de la lumidre, etc.; cit. Bot. Centralbl. 1880, 
p. 1460. 

3 Pfeffer, Arbeiten d. Bot. Institut.s zu Wiirzburg-, ed. by Sachs, Part 1. 



6^2 

produce leaves which at first unfold as green leaves and later, when they 
become old, become light yellow in places. In the same way, many yellow 
garden varieties of woody plants only become a bright yellow with strong 
insolation ; in the shade they remain green. 

Ewart^ observed in tropical plants a complete bleaching of the chloro- 
phyll grains as a result of an excess of Hght. If thellight stimulus increases 
above the specific optimum, the optimal and maximal development of gases 
at first continues for a short time, but then follows a condition of exhaus- 
tion^. If this excessive stimulation does not last too long, the plant can 
recover its normal activity. This over-stimulation can also occur imder 
our normal light conditions, if the plant, by nature, belongs among shade 
plants. Weiss^ cites a fine example of this in Polypodium vulgarc, a de- 
cided shade plant, as contrasted with Oenothera biennis which is distinctly 
a sun plant. With a favorable temperature, the latter produced about 
three times as much carbon dioxid in direct sunlight as in diffuse light ; 
while the former assimilated more energetically in diffuse light. Diffuse 
daylight can, in fact, act to arrest the growth of roots which are accustomed 
to the dark, as Kny found in lupines, cow beans, and water cress*. In this, 
he observed in lupines usually a decrease of growth in thickness and a 
retarding of the development of the central cylinder, if the growth in length 
increased. 

The works of Dixon, Dixon and Wigham, Joseph and Prowazek, Max 
Koernicke and Hans Molisch^ prove a very decided arrestment of growth 
from the use of Rontgen and radium rays. 

An abnormal thickening and a wrinkled surface were observed in pea 
roots, which could be traced, apparently, to differences in internal tension. 
Contractions are produced by the increase in the radial diameter of the cells 
of the inner bark parenchyma, together with a shortening of the longi- 
tudinal diameter. It was found in other experiments with vetches and horse 
beans that the roots turned brown and their growth was arrested. But 
after 8 to lo days they grew further, after having thrown off the outermost 
tips in the form of brown caps, and formed new root tips directly behind 
these. Normal lateral roots were produced immediately. The arrest of 
growth 'is less in organs containing chlorophyll. In seedlings a cessation in 
the growth in length has been observed but no dying back. The leaves 
became somewhat smaller than in normal specimens. Dixon** could not 



1 Ewart, A. J., The effects of tropical insolation; cit. Just's Jahresber. 1899, 
I, p. 87. 

2 Pantanelli, Enrico, Abhang-ig-keit der Sauerstoffausscheidung- belichteter 
Pflanzen von ausseren Faktoren. Jahrb. f. wiss. Bot. 1903, Vol. XXXIV, p. 167. 

3 "Weiss, Fr., Sur le rapport entre I'intensite lumineuse et I'energie assimilatrice 
Chez les plantes appartenant k des types biologriques differents. Compt. rend. Paris 
CXXXVII, 1903, p. 801. 

-I Knv, Lr., tiber den Einfluss des Lichtes auf das Wachstum der Bodenwurzeln. 
Jahrb. f. wiss. Bot. 1902, Vol. 28, p. 421. 

5 Seckt, Hans, Die Wirkung- der Rontgen- und Radiumstrahlen auf die Pflanze. 
Sammelreferat. Naturwiss. "Wochenschrift, 1906, No. 24. 

Dixon, Henry, Radium and plants. Nature, London LXIX; cit. Just's Bot. 
Jahresber. 1903, II. p. 567. 



^7Z 

find heliotropic curvature in young cress seedlings at a distance of one cen- 
timeter from a glass tube containing 5 g. of radium bromid. 

In bright sunlight, we find that parts of the plant often not only become 
yellow but even turn brown and die^. That this dying is a specific light 
action and not a result of too great an increase in temperature is proved by 
the fact that the chlorophyll remains unchanged" in temperatures varying 
from 30 degrees below zero to 100 degrees above zero and, on the other 
hand, that the destruction takes place with rays of shorter wave length 
which influences most of all the processes of growth and protoplasmic 
movement. 

The rays of a concentrated sun image, which have passed through 
ammoniacal copper oxid often cause death after a few minutes, while the 
same amount of light, after passing through a solution of iodine in carbon 
disulphid (which lets only the outermost red rays pass through) scarcely 
causes any destruction, or only a ver\^ tardy one''. In this red light, how- 
ever, an extensive warming takes place, but not in the blue light. 

Among the phenomena arising from an excess of light belongs also the 
production of shadow pictures, i. e., intensive green pictures of overshad- 
owing organs on a strongly lighted leaf surface. No destruction of the 
chlorophyll apparatus necessarily takes place here, only a change in the 
position of the chloroplasts is produced. 

Observations, made by Bohm, Famintzin, Borodin, Stahl and Frank, 
proved that, in sunlight too high for the special need of the plants, the 
chlorophyll grains begin to move from the cell walls, parallel to the upper 
surface of the leaf, towards the walls at right angles to them. The chloro- 
plasts pass from the epistrophe to the apostrophe and thereby bring about 
the lighter color of the too strongly lighted part. 

A further observation which can be made easily is the appearance of a 
red color with too strong lighting in the green leaves of plants which turn 
red in the autumn, as, for example, when the under sides of sweet cherry 
leaves are turned uppermost. In the same way, a decided brownish red 
color may be found in many plants, especially in those with fleshy leaves, 
when brought in spring from the shaded conservatories into an open, sunny 
place. Molisch* has investigated such cases. He proved in Aloe and 
Selaginella that anthocyanin is not formed in the cells but that the chloro- 
plasts themselves turn red and become green again when put in the dark. 
In some varieties of Selaginella, red or brownish red chloroplasts were 
observed, colored by carotin, especially above a place where the stem had 
broken. 

The process most important agriculturally and most significant 
hygienically, however, consists in the destructive action of the sunlight on 



1 Bohm, Versuchsstationen 1877, p. 463. 

2 TViesner, Die naturlichen Einrichtungen zum Schutze des Chlorophylls. 
Festschrift; cit. Bot. .Jahresber. 1876, p. 728. 

3 Pring-sheim. Jahrb. f. wiss. Bot. 1879, Vol. 12, p. 336. 

4 Molisch, H., Uber voriiberg-ehende Rotfarbung der Chlorophyllkorner in 
Laubblattern. B. der Deutsch. Bot. Ges. 1902, XX, p. 442. 



674 

pathogenic fungi and especially on bacteria. Pfeffer^ says, "It seems that 
all pathogenic bacteria are killed by a sufficient exposure to sunlight." 

That artificial light acts in the same way as sunlight is proved, for 
example, by the experiments made by Dixon and Wigham- with radium 
rays. Cultures made with Bacillus pyocyaneus, B. typhosus, B. prodigi- 
osus and B. anthracis showed that the /5 rays of radium bromid called forth 
a perceptible arrest of growth. After 5 mg. of radium bromid had acted 4 
days on the bacteria, at a distance of 4.5 mm., their growth, at least, was 
stopped, if they were not all killed. 



1 Pflanzenphysiologie, 2d ed., Part II, p. 319. 

.2 Dixon, Henry H., and Wig-ham, J., Action of Radium on Bacteria. Nature, 
London LXIX; cit. Just's Jahresber. 1903, II, p. 567. 



SECTION HI. 



ENZYMATIC DISEASES. 



CHAPTER XV. 



DISPLACEMENT OF ENZYMATIC FUNCTIONS. 



General Discussion. 

Present investigations tend to the theory of perceiving, in the majority 
of metaboHc processes, the action of enzymes. We would Hke to divide 
these enzymes into two groups, according to their activity, which may be 
called constructive and destructive. In the process of formation of the 
vegetative organism, we obsen^e in germination, i. e., in the preparation for 
the vegetative development, a prevalence of the destructive activity since 
the reserve substances are dissolved and carried over into usually instable 
groups of substances, capable of being transported. The activity of the 
vegetative apparatus leads gradually to the precipitation of reserve sub- 
stances and we term this activity constructive. Its final goal may be recog- 
nized in the maturation of the seed. 

From this may be perceived an antagonism in the occurrence of the 
most important material groups, which antagonism may be determined by 
the fact that, in abundant deposition of starch, the sugar content, as well 
as the amount of tannin and of organic acids, decreases. If, on the other 
hand, sugar, tannin and acids are abundantly present, the precipitation of 
starch remains small. If the amovmt of starch is large, the formation of 
the proteids in the cell from asparagin or other nitrogenous compounds is 
abundant. In the preponderance of sugar and acids, the nitrogenous com- 
pounds remain in an instable form. I would like to contrast this condition 
of the plant parts as "immature/' with the "mature" condition which is 
distinguished by an abundance of reserve materials. 

The dififerent factors of growth that influence constantly the plant 
body sometimes let one group of enzymes prevail, sometimes another. It is 
not necessary that the enzymes be destroyed. Their action need only be 



6/6 

temporarily arrested. Pozzi-Escot^ furnishes an example of this when dis- 
cussing the Philothion. "Reductases," he thinks, which are identical with 
Loew's catalase, "are distributed everywhere like oxydases, and act antag- 
onistically" . . . De Rey-Pailhade has proved that reductases are 
quickly destroyed by an oxydase in the presence of free oxygen, and, con- 
versely, Pozzi-Escot proves that, under certain circumstances, the action of 
an oxydase can be "paralyzed," when the reductase is present in great ex- 
cess. Thus, in temporary fluctuations in the cell contents, a reductase can, 
for the moment, make the oxydase inefifective, and conversely. Pozzi- 
Escot perceives the most important role of the reductases to be their action 
on H^ Oo in the processes of respiration as well as in photo-synthesis. 

Antiferments occur in other cases, as Czapek-, for example, has dem- 
onstrated. He found an arrestment in the further oxidation of the homo- 
gentisin acid, originating from tyrosin, in organs stimulated geotropically 
or heliotropically by the presence of an anti ferment. 

In general, we perceive from the results of cultivation and some experi- 
mental investigations, that light and heat favor catabolism, i. e., disposition 
of groups of solid reserve material, while darkness and cold either maintain, 
or cause an increase in the amount of colloidal food materials. 

Under normal climatic conditions, the time at which prevailing condi- 
tions in the cell contents exhibit the conditions characteristic of the 
destructive activity, lies actually in the colder seasons of the year. We 
find processes of germination especially in autumn and spring, but, on the 
other hand, constructive activity, i. e., the deposition of reser^^e materials, 
•in the summer. 

The necessary regular succession of these periods depends, however, 
not only on the weather but also on all the nutritive factors, as, for example, 
the supply of water, the amount and constitution of the nutrients, and, 
besides this, on dififerences in cultivation, viz., pruning, etc. A number of 
diseases oflfer examples for the last point, i. e., when the organism is com- 
pelled, by the sudden removal of considerable amounts of the plant body 
(branches and leaves), to mobilize again the stored material at a time when 
the period of storing should prevail and, thereby, to return to the vegetative 
period for the formation of new shoots. In regard to the supply of food 
we find, for example, that excessive amounts of nitrogen postpone the 
period of storing up reserve materials since growth is continued beyond 
the normal size. 

Thus, the enzymatic work is postponed ; the mobilizing enzymes now 
prevail and the plant, with organs in active growth, enters upon a period 
of weather which, in the normal course of events, demands mature plant 
parts, rich in reser\'e materials. It becomes, therefore, susceptible to para- 
sitic and non-parasitic attacks. 



1 Pozzi-Escot, E., The Reduciner Enzymes. American Chem. Journ., Vol. XXIX, 
1903, p. 517; cit. Bot. Centralbl. 1904, No. 49. 

2 Czapek, F., Antifermente im Pflanzenorg-anismus. Ber. d. Deutsch. Bot. Ges. 
1903, Vol. XXI, p. 229. 



^77 

It is, however, not only the momentary displacement of the enzymatic 
functions which can act disadvantageously on the organism, but the number 
of subsequent phenomena must necessarily be connected with it, which will 
manifest themselves only in the next generation. If, for example, we keep 
in view the lengthening of the period of growth, induced, as experience 
shows, by an excess of nitrogen, the immediate result is that the production 
of seed, which normally occurs at the period of the greatest amount of heat 
and light, is carried over into a cooler time when the light is poor. The 
seed thus produced, therefore, does not have sufficient time and proper 
climatic conditions to carry on all the processes necessary for the formation 
of reserve materials. The seed is harvested in a condition in which the 
mobilizing enzymes are still considerably, active and it, therefore, is suscep- 
tible to attacks by parasites affecting the fully matured seed. It has been 
proved experimentally that immature seed is destroyed more quickly by 
moulds. Even if the immature seed is not destroyed, and develops the 
following season, the plant thus produced will necessarily be influenced in 
its first growth by the greater amount of water content in the seed and the 
lesser amount of resen^e materials. In this connection the following gen- 
eration is the product of the preceding one, and, therefore, will reproduce 
by inheritance conditions of weakness. 

Everything that is true of the seed, must also hold good for all other 
permanent organs. The bud and the maturation of the branch are, in the 
same way, the product of the preceding period of growth and the manner 
of their further development depends primarily on the degree of maturity 
to which they attained in the previous year. 

Displacements of the enzymatic functions, therefore, are continued 
from one period of growth to another and the diseases, subsequently 
described, are examples of the inheritance of physiological disturbances. 

Albinism (Variegation). 

The phenomenon, sought by gardeners and propagated by grafting 
(which may, in fact, be carried over to the stock), manifests itself in the 
whitish appearance of places which sometimes have a circular form in the 
diachyma (mesophyll), sometimes appear as wedge-shaped stripes between 
the ribs, and sometimes as connected zones along the edge of the leaf. The 
intensity of the white coloration varies. The most diverse transitions from 
the purest white to quince yellow are found, which in many plants give still 
further color shades because of the occurrence of reddish tones. In this 
way is produced the phenomenon called variegation. 

A very weU-known example of this white spotted condition is found 
in the ribbon grass of our gardens (Phalaris arundinacea L., Phalaris picta 
L.), in which the white parts occur alternately as stripes between the veins. 
A toy species of the ash leafed maple (Acer Negundo L.) is still more 
striking. At times this shows perfectly white foliage. The family of the 
Aroideae might be named as examples of the occurrence of variegation as 



678 

well as of white coloring. Among these, the calla, frequently cultivated in 
the house (Zantedeschia aethiopica), shows leaves which often are as pure 
white as the funnel-shaped blossom sheath. The bright colored calladia, 
greenhouse favorites, are related to the Zantedeschia. Among them a few 
are only specked with white, others have white and red spots, and many 
finally only red spots. 

The white spotted condition of the flowers and the more rare albinism 
of fruit are difficult to distinguish. Of the latter, Dufour^ has described 
interesting cases in grapes. 

There prevails, especially in practical circles, an earnest hesitation in 
accepting the theory which ascribes the white variegated leaves to the 
phenomena of disease. Yet, we believe that this opinion must be defended. 
If we investigate a considerable number of plants with variegated leaves, 
we find all gradations in the cells from the normal chloroplasts to the entire 
disappearance of the chloroplastids. The parts of the plants which appear 
yellowish often have chloroplasts which appear as yellow, sponge-like balls 
or discs in the cells ; the purer white the plants are, the fewer are the even 
colorless chlorophyll bodies; and the m.ore the cytoplasm assumes the ap- 
pearance of a soft, uniform wall lining. The intercellular spaces contain 
more air and at times are larger. 

The assimilation of carbon dioxid also ceases with the disappearance 
of the chloroplasts. Cloez' and later Engelmann^ found that the leaves 
assimilate carbon dioxid only in proportion to their chlorophyll content. 
The different gradations in the yellow variegation arise from lesser quanti- 
ties of the same chlorophylline and zanthophyll, than occur in the normal 
green leaves* and their assimilator)^ activity is in accordance with this. 

In pure white leaves the chlorophyll does not form and the chloroplasts 
are poorly developed. In the yellow forms, chloroplasts are found at least 
in the bud and often later but the degree of degeneration of the chloroplasts 
depends on their proximity to the pure white zone. The analyses given by 
Church^ serve as a good confirmation of this. He used white variegated 
forms of maple (Acer Negundo), Ivy (Hedera Helix) and Holly (Ilex 
aquifolium) : 

Acer 

They contained white green 

leaved leaved 
per cent, per cent. 

Water 82.83 72.70 

Organic substances 15.15 24.22 
Ash 2.02 3.08 



Ilex 


Hedera 


white green 
leaved leaved 


white green 
leaved leaved 


per cent, per cent. 


per cent, per cent, 


74.14 62.83 

23.66 35.41 

2.20 2.47 


78.88 66.13 

18.74 31.63 

2.38 2.24 



1 Defour, J., Panachierte Trauben. Extr. Chronique agric. du canton de Vaud; 
cit. Zeitschr. f. Pflanzenkrankh. 1904, p. 286. 

2 Compt. rend. LVII, p. 834. 

3 Engelmann, Farbe und Assimilation, Bot. Zeit. 1883, Nos. 1 and 2. 

4 Kranzlin, G., Anatomisclie und farbstoffanalytisclie Untersucliungen an 
panachierten Pflanzen. Inaug.-Diss. Berlin 1908. 

5 Church, Variegated leaves. Gardeners' Chronicle 1877, II, p. 586. 



679 

The green leaves show, therefore, in contrast to the white spotted ones, 
considerably greater amounts of dry substances, while in the latter the ash 
constituents (as found universally where disturbances in nutrition make 
themselves felt) form a greater percentage of dry substance. The nitrogen 
content in the white leaves of the ivy and the holly was greater in propor- 
tion to the dry substance. This result is also explicable ; for, if the chloro- 
phyll apparatus, without doubt necessary for the production of starch 
grains and other carbohydrates, is only scantily present, the amount of dry 
substances is reduced and the absolutely smaller amount of substances con- 
taining nitrogen appears relatively increased. The fact that the substances 
soluble in alcohol and ether in the white leaves of ivy and holly amount to 
about half that in the green leaves likewise may not be considered surprising. 

The percentages in the composition of the ash are very important. 
They are as follows : — 

Acer Ilex Hedera 

white green white green white green 

per cent, per cent, per cent, per cent, per cent, per cent. 

Potash 4S-05 12.61 35-30 16.22 47-20 17.91 

Lime 10.89 39-93 21.50 34.43 12.92 48.55 

Magnesia 3.95 4.75 3.23 2.43 i.ii 1.04 

Phosphoric acid... 14.57 8.80 9.51 7.29 10.68 3.87 

Iron oxide ? ? 3. 11 3. 11 2.62 2.31 

It is evident from these figures that organs without pigmentation 
approximate the condition of young green leaves and have, therefore, failed 
to develop in a normal manner. Griffon^ has come to the conclusion that 
plants without pigmentation behave in general like etiolated ones, which we 
have also compared to arrested development. In the yellow transitional 
stages the results of variegation are very different. In Abutilon Thomp- 
soni I found the cell content in many leaves still arranged as in perfectly 
green parts, i. e., provided with chloroplasts, their edges roundish angular, 
which were normally arranged against the walls but were a pale yellow, or 
colorless, and had a strongly granulated content. In other cells the sub- 
stance of the chloroplasts was united into irregular Agranular balls which 
took on a blue color with iodine, glycerine, and in part also with sulfuric acid 
and which might be called carotin. KohP also found carotin (etiolin), in 
the investigation of golden yellow leaves, besides /9-zanthophyll and 
phyllofuscin. 

The difference in the thickness of the leaf, i. e., the noticeably lesser 
thickness of the pure white parts in contrast to the pure green parts, 
decreases the more the color tone varies from the pure white ; i. e., the more 
yellow the places in the leaf become. Timpe^ also calls attention to this 

1 Griffon, Ed., L'assimilation chlorophyllienne et la coloration des plantes. 
Annal. sc. nat. VIII, 1899; cit. Bot. .Tahresber. 1899, I, p. 151. 

2 Kohl, P. G., Untersuchung-en iiber das Carotin und seine physiologische 
Bedeutung in der Pflanze. Leipzig, Borntrager, 1902, IX. 

3 Timpe, H., Beitrage zur Kenntnis der Panachierung. Dissertat., Gottingen, 
1900. 



68o 

circumstance and lays emphasis on the fact that the slime cells are fewer 
in the non-pigmented parts of plants which bear the mucilage cells (Ulmus, 
Crataegus). On the other hand, the content of tannin in the white parts is 
usually proved to be greater. Starch is found rarely but, according to 
Timpe, in a sugar solution is often formed more abundantly by the non- 
pigmented places than by the green ones. Monocotyledons store up no 
starch in a sugar solution. 

It is stated by other authors that the pure white places contain no starch 
since assimilation does not take place there. These apparent contradictions 
are explained by the transitional stages to a golden yellow color which, 
indeed, contain no chlorophyll but have zanthophyll and carotin and elim- 
inate oxygen in the light (like etiolated leaves)*. 

An interesting fact is that in many plants a lack of pigmentation may 
be communicated to the stock by grafting. Meyer^ reported experiments 
of this kind with positive results as early as 1 700-1 710 with Jasminum 
officinale. "If a branch of Jasminum with variegated leaves is grafted on 
the healthy trunk of the same Jasminum, the other branches above and 
below the scion likewise bear variegated leaves." Later Lindemuth- and 
recently Baur^ have studied the question especially. Baur has advanced the 
theory that the yellow forms may be considered to be sport varieties, or 
mutations, which in part persist in the seed. The pure white, however, 
should be distinguished from these as examples diseased by infection. At 
any rate, the infecting body may be no living creature, but an unknown 
material something, a virus which can increase in amount within the dis- 
eased plant. This virus can be a metabolic product of the diseased plant 
which is able to infect the young chloroplasts in such a way that they cannot 
develop tc normal organs, but to malformations in which then the same 
virus is formed anew. However, it may be a metabolic product of the 
diseased plant which, in a certain sense, has the capacity for growth, i. e., 
can split off substances from other compounds identical with it, or can 
synthetically construct new substances of this kind**. 

This line of thought has already been expressed in a more precise form 
by Pantanelli^ and later supplemented. He says*', "the albinism is not an 
infectious disease, but a constitutional one, the first sign of which occurs as 
an abnormal accumulation of destructive and primarily oxidizing enzymes." 
"The substances, causing the destruction, spread through the leptome 



* Kohl, loc. cit. 

1 Meyen, F. J. F., Pflanzenpathologie, Berlin, 1841, p. 288. 

2 Lindemuth Vegetative Bastardei'zeug-ung durch Impfung". Landwirtschaftl. 
Jahrbiicher 1878, Part 6. Gartenflora 1901, 1902, 1904. 

3 Baur, Envin, Zur Aetiolog-ie der infektiosen Panachierung'. Ber. d. Deutsch. 
Bot. Ges. 1904, Vol. XII, p. 453. Further statements on the infectious chlorosis of 
the Malvaceae and other similai phenomena in Ligustrum and Laburnum. Ber. d. 
Deutsch. Bot. Ges. 1906, Part 8, p. 416. 

4 Baur, E., tJber die infektiose Chlorose der Malvaceen. Sitzungsber. d. Kgl. 
Preuss. Akad. d. Wiss. January 11th, 1906. 

5 Pantanelli. E., Studii su I'albinismo nel regno vegetale. Malpighia. Vol. 
XV-XIX (1902-5). 

6 Pantanelli, E., tJber Albinismus in Pflanzenreich. Zeitschr. f. Pflanzenkrank- 
heiten 1905, p. 1. 



68i 

bundles, either because of an energetic influence due to adjacent and com- 
municating protoplasts, or of a material transportation by means of sieve 
tubes and analogous elements throughout the entire body ; they reach at last 
the developing petioles and then the main ribs of the leaves. Here they 
influence all the parenchyma cells with which they are connected clearly 
more energetically or because of a poor nutritive provision and removal." 
The transference of the phenomena from the scion to the stock, therefore, 
comes about if, in grafting, the leptome connection in the tw^o component 
parts has been established. 

This theory is based on experimental studies. It has been proved by 
chemical investigation that "the protoplasm and plastids are gradually 
attacked by abnormal formations of strongly destructive enzymes and 
digested by them." In some intensive cases of albinism no accumulations., 
how'ever, of inorganic, or organic substances, or sugar, may be proved. 

A determination made by Pantanelli on Ulraus leaves throws light on 
the behavior of the nitrogen compounds. He pulverized green and non- 
pigmented leaves with the necessary precaution and let the pulp stand 8 
days in a cylinder. The original amount of water in the green leaves 
averaged 60.67 P^^ cent., that in the non-pigmented leaves of the same tree, 
at the same time, 73.8 per cent. 

The green leaves contained (in percentages of the dry weight). 

In the beginning ' After 8 days 

Nitrogen as a whole 3-355 per cent. 33250 per cent. 

Proteid nitrogen 3-324 " 0.9212 '' 

Non-proteid nitrogen 0.031 " 2.4050 " 

Non-pigmented leaves contained (in percentages of the dry weight) : 

In the beginning After 8 days 

Nitrogen as a whole 2.681 per cent. 2.576 per cent. 

Proteid nitrogen 2.274 " 0.604 " 

Non-proteid nitrogen 0.407 " 1-972 " 

Autolysis in the sap of the variegated leaves is, therefore, compara- 
tively more extensive than in the green ones. The amount of nitrogen in 
non-pigmented organs is considerably less, but the percentage of non-proteid 
nitrogen compounds is greater. The richly abundant phosphoric acid must 
be present in some other combination since lecithin cannot be formed nor 
the chloroplast be developed. Also, according to Pantanelli's investigations, 
an enzyme which breaks up the starch seems to be present more abun- 
dantly in the variegated leaves than in the green ones, at least when they are 
young. 

In the second edition of this manual (p. 195), I have already referred 
to the nitrogen poverty of the non-pigmented parts and there expressed 
the following opinion : — in the normally nourished leaf cell so much cyto- 
plasm is present that not only material can be furnished for the develop- 
ment of the cell wall, but the chloroplasts can also be produced abundantly. 



682 

If the supply to the young cells is cut off too soon, because the material, 
increasing the amount of protoplasm, is supplied too scantily, and the cell 
wall becomes old prematurely, the cell can have performed only the first 
part of its task, the formation of the wall, and has nothing left over for the 
formation of the apparatus which produces reduction and increases the dry 
substances, nor for its maintenance. This same poverty must occur in the 
normal cell if it gets into conditions of growth which cause an accumulation 
of destructive, i. e., amylolytic enzymes, whereby it is again carried back 
toward the young stage. If the plant is brought under conditions which 
favor normal vegetative activity (shade, moisture and heat) the non-pig- 
mented parts of the axis tend to produce green leaves. A discovery of 
Lindemuth's confirms this observation. He proved that intense Hght actu- 
ally favors albinism. Ernst^ mentions that in Caracas Solanus aligerum 
Schlecht., common to that region, is found not infrequently with variegated 
leaves. This occurs, however, only on poor soil. Specimens with strongly 
variegated leaves, transplanted to better soil, become green. With Urtica 
dioica, Beijerinck-, even in one year, succeeded in bringing back the green 
form from the variegated form by means of cuttings. 

Tissues, with a less concentrated cell sap are, however, less resistant. 
Actually, the white leaved parts of the plants are more sensitive to heat, 
frost, and drought, and die sooner. We find more abundant examples in 
the white leaved Acer Negundo, in which even the bark of the branches 
becomes variegated. Almost every year, summer sunburn and winter frosts 
kill the most exposed branches. Such cases also occur in conifers^. In 
the same way seedlings with white cotyledons and plumules are very easily 
destroyed. Not infrequently I have found pure white seedlings, or white 
ones with a reddish tinge, in larger sowings of various kinds of fruits. 
These were always treated with special attention but died after some time, 
in case they did not begin to produce green leaves. Similar observations 
have been made also by others, for example, on Phormium tenax (de Smet), 
Passiflora quadrangularis as well as on Dahlia variabilis, Dianthus Caryo- 
phyllus, and the Liliacea (Lindemuth). A scarcity of reserve substances 
in non-pigmented branches explains also the further observation that their 
cuttings grow with greater difficulty than those from the green parts of the 
same individual. Consider, for example, hydrangeas with pure white 
leaves and geraniums from the group "Miss Pollack." 

Lindemuth observed in Abutilon that the non-pigmented leaves are 
usually smaller and have a shorter life period. We would recall in this 
connection the phenomenon, occurring not infrequently, in our wild plants, 
that when one-half of the leaf is white, the other half green, the former 
remains shorter and the latter, on this account, curves about the white half 
in the form of a sickle. (Cichorium, Beta.) In marbled leaves, the white 



1 Botanische Miscellaneen. Bot. Zcit. 1876, p. 37. 

2 Beijerinck, M. W., Chlorella variegator, ein bunter Mikrobe; cit. Bot. Cen- 
trabl. G. Fischer, 1907, p. 333. 

3 Zeitsch. f. Pnanzenkrankh. 1896, p. 361. 



683 

fields of a leaf often appear distended, the green ones wrinkled, or blistered. 
The stems also at times, in the non-pigmented part, show some shortening, 
as is proved by the variegated Kerria japonic a, of which green shoots on 
the same stem and of the same age are at times half a meter taller than 
those bearing white leaves. Sambucus, Weigelia and others, behave in 
this way. 

in my opinion, albinism is a form of arrested development which occurs 
more rarely in wild plants but to an increasing degree in cultivated ones 
and manifests itself in the poorer nourishment of the dififeretit tissvie ele- 
ments. The result of this is that, either the chlorophyll apparatus does not 
mature at all, or soon falls victim to destructive enzymes. The lack of any 
accumulation of reserve materials, or, at most, a scanty one, is connected 
with this and explains the increased collapsibility of the tissues. 

Of the causes producing albinism, the pressure conditions in the bud 
should come first under consideration which arrest the development of the 
conducting system and thereby hinder the sufficient filling of the cells with 
plastic material even in the embryonic condition. This would explain the 
phenomenon of the sudden development of a non-pigmented shoot from the 
bud of a plant which had been green up to that time. In regard to cultural 
influences, experience shows that a relative excess of light acts favorably, 
for we see that often a condition of pure white leaves occurs ver)^ inten- 
sively with direct, strong insolation and is retained longest, but decreases, 
when shade and a sufficient supply of water and nitrogen give the leaf time 
to develop more slowly and let its vegetative functions act longer, i. e., 
preventing a premature end of life. 

Timpe^ cites in his latest work a phenomenon which has been repeat- 
edly tested experimentlly. He repeated the experiments first described by 
Molisch- with the white and green variegated species of Brassica oleracea 
acephala and obtained the same result, viz., that the brilliant white color of 
the leaf surfaces, which reaches its greatest development in winter in a 
cold frame (up to February), decreases almost at once and finally disappears 
if the plants are brought into a warm place. Molisch transferred white 
variegated plants from the cold frame at 4 degrees to 7 degrees C. into a 
hot bed at 12 to 15 degrees C. All the leaves already formed turned green 
in from 8 to 14 days ; those newly formed appeared green at once. Returned 
to the cold frame, the specimens again formed leaves variegated with white. 
Here belongs also Weidlich's statement^ that Selaginella Watsoniana must 
be cultivated in a temperature of 10 degrees C if it is to form white tips. 
In these cases, therefore, the increase in the vegetative functions, producing 
the loss of albinism, is conditioned by the increase of heat; while in other 
cases, according to the nature of the plant and other local nutritive condi- 
tions, the variegated leaves can be brought back to the optimum of their 



1 Tempe, Heinrich, Panachieruns: und Transplantation. Jahrbuch d. Hamburgr 
wiss. Anstalten XXIV, 1906, Beiheft 3. 

2 Ber. d. Deutsch. Bot. Ges. XIX, 1, p. 32. 

3 Gartenflora 1904, p. 585. 



684 

functions and to the normal formation of chlorophyll by decrease of light 
and heat; or by the increase of the nitrogen or potassium supply, thus pro- 
longing the period of growth. 

A scanty supply of material frequently manifested in the increase of 
tannin and the absence of starch, the small size of the cell and the increase 
of the intercellular spaces, is also emphasized by Timpe in his carefully 
worked out experiments. He describes a phenomenon for Ulmus which 
seems strange to him but is exactly the best proof of our theory. In this 
the luxuriant spring growth of shoots variegated with white developed per- 
fectly green foliage after the tree had been set out; but the midsummer 
growth, with a lack of water and excess of light and heat, again showed 
the variegation*. 

If, however, albinism consists in the premature ending of life, i. e., in 
the suppression, or arrestment, of the work of the chlorophyll apparatus, the 
destructive enzymes, even if not increased in absolute amount, still obtain 
a preponderance in the cell because those which cause the formation of the 
reserve materials, have been too little developed due to the lack of chloro- 
phyll activity. The equilibrium otherwise formed in the cells containing 
chlorophyll is destroyed. 

We, therefore, do not need to assume the formation of a "virus" : — • 
a group of materials acting poisonously, which must be produced and 
increased in the plant, — in order to explain albinism and the phenomena of 
disease related to it (the mosaic disease, shrivelling disease, etc.). It is 
simply a change in the functions, i. e., a different direction of the mole- 
cular motion to which we must trace back, however, all metabolic processes. 
If this changed formation of substances is a movement, it can continue until 
some other form of molecular motion causes its arrestment. The non- 
pigmented part of the plant is, therefore, the carrier of an abnormal motion 
in its substances and on this account it would not seem strange if this motion 
is continued as soon as the paths, i. e., the vascular bundles (according to 
PantaneUi, the leptome parts), of two separated individuals are united, as 
is the case in grafting. 

If we consider albinism not as a phenomenon coming from the ranks 
of the other phenomena of variegation but only as the most extreme case of 
a process representing a decrease in the amount of chlorophyll, it can no 
longer seem strange that plants, variegated with yellow and, therefore, less 
irritated, can still be brought to the production of seeds in which the same 
direction of the metabolic motion is continued, i. e., that the seeds furnish 
plants with yellow variegation. 

The Mosaic Disease of Tobacco. 

The most recent authors, who have written on albinism, have already 
mentioned the relation of this phenomenon to the mosaic disease of 
tobacco. 



* LiOC. cit., p. 68. 



685 

This name originated with Adolph Mayer, who in ]u\y, 1879, when the 
disease had occurred to an alarming extent in Holland, received some dis- 
eased plants from the Society of Agriculture (Department Wijk bij 
Duurstede) for investigation. He published the results of his experiments 
in 1885, in a Dutch periodical and in the following year in the "Landwirt- 
schafthchen Versuchsstationen"^ According to F. W. T. Hunger- Van 
Swieten in 1857 had first called attention to the mosaic character of the 
variegated leaves of tobacco in the Dutch plantations but in his later studies 
on the cultivation of tobacco in Cuba, did not mention the disease which then 
was called "Rost." At present the disease may exist in any country grow- 
ing tobacco and, accordingly, has received any number of names. Thus 
Hunger mentions that in Holland it is not only called "Rost" but in places 
"Bunt" or "Faule." In Germany the name "Mosaikkrankheiten" holds 
good. In places it passes as "Mauche ;" in France it is called "La Mosaique" 
or "Nielle" or "Rouille blanche;" in Hungary it is called "Mosaikbetegsege" 
and the Tartars in southern Russia call it "Bosuch." In Italy it is described 
under the name "Mai de Mosaico, or "Mai delta holla." In America, in 
the northern states, it is called "Calico" or "the Frenching disease;" in the 
southern states, on the other hand, "Brindle" or "Mongrel disease" The 
plantations in Java, Borneo and Sumatra also suffer heavily. The Javan- 
ese call the disease "Poetih" while it is known in Deli by the Chinese name 
"Peh-sem"^. , 

The mosaic disease may at present be considered the most dangerous 
disease of the tobacco plant. This explains why it has been thoroughly 
studied recently from several points of view but the results are often con- 
tradictory. While some investigators, retaining the old theory with great 
tenacity, wish to find microbes and think they have found them, others 
defend the theory that an infection disease is present here, the cause of 
which must be sought in inexpedient enzymatic activity. 

The diversity of opinion is explained partially by the fact that different 
phenomena have been included under the mosaic disease which do not 
belong together. On the other hand, however, the disease can actually 
appear under different forms. 

We follow Delacroix* in describing its symptoms. He distinguishes 
two stages: — i, loss of color; 2, changes in the form of the diseased leaves. 
In the first groupvof symptoms, the edge of the leaf shows sharply outlined, 
various colored spots of a faded green, which shades off into a whitish color 
but not into a yellow green as in chlorosis; the pale green parts have spots 
of dark green color, which is even darker than that of the normal leaf. 
The dift'erences in color become more apparent when the leaf is held 

1 Mayer, Adolf, Die Mosaikkrankheit des Tabaks. Landw. Versuchsstat. 18S6, 
Vol. XXXII, p. 450, Part III. 

2 Hunger, F. W., Untersuchung-en und Betrachtungen iiber die Mosaikkrank- 
heit der Tabakspflanzen. Zeitsch. f. Pflanzenkrankh. 1905, p. 257. 

3 Hung-er, loc. cit. 

4 Delacroix, Georges, Recherches sur quelques maladies du Tabac en France. 
Paris 1906, p. 18. Extrait des Annales de I'lnstitut national agronomique, 2 ser., 
Vol. V. 



686 

against the light, and, by feeHng the leaf, it is noticeable that the dark green 
places are somewhat thicker than the pale ones. Before Delacroix, Iwan- 
owski^ had already emphasized the fact that the lateral shoots, developing 
from the axes of diseased leaves, have the mosaic disease. This circum- 
stance is very important and characteristic of the disease in which the loss 
of color occurs in the young leaves; as a rule, mature leaves do not be- 
come diseased. Often the dark green places become somewhat convex so 
that the surface of the leaves is somewhat wrinkled; in other, and rarer 
cases, a reduction of the leaf surface sets in which can increase to such an 
extent that, on the whole plant, only the mid ribs are present but no blades. 
This latter characteristic has been mentioned by HeintzeP and Iwanowski. 
but, according to Hunger' it is not typical of the disease, for he had also 
observed it in Deli in healthy plants on open ground. 

Therefore, in the mosaic disease, we find the same characteristics as in 
albinism; a sharp delimitation of the spots, a greater thickness of the green 
places, and. at times, a reduction of the leaf surfaces, which, in the varie- 
gated parts, remain small. This can also be transmitted artificially and 
probably follows the same paths, i. e., the leptome. The only difference is 
that the mosaic disease can be transmitted considerably more easily. Ever}' 
particle of sap which falls from a diseased plant into an injury in a healthy 
one is enough, under certain circumstances, to cause infection. We will 
cite, as example, the description of an infection experiment made by 
Koning*. On the 5th of July he cut the stem o£ a perfectly healthy plant 
as far as the vascular bundles and inserted in the cut a small piece of the 
spotted leaf from a diseased plant. On the 20th of July a dark fleck could 
be seen near the edge of a young leaf, between the veins. In the course of 
the next few days, specks appeared also on the other young leaves while 
the leaf itself took on "an uneven, irregular appearance due to the increase 
of the palisade tissue." The edge of the leaf appeared in places to be 
strangulated, or slightly lobed. Later these spots dried up, after having 
assumed a reddish brown color. Koning perceived concentric zones in the 
larger spots, of which the outermost zones were the darkest. Not infre- 
quently he found that whole pieces had fallen out of the leaf. The latter 
characteristics are not mentioned by other observers, which fact supports 
our theory that the disease can present different aspects in diff'erent places 
and in different varieties of tobacco. 

Koning gives only scanty notes on the anatomy of the diseased leaves. 
In the very youngest stage of the spots, where no differentiation of palisade 
and spong}^ parenchyma has set in, dark stripes appear between the cells 
which represent strikingly large, air-filled intercellular spaces. These are 

1 Iwanowski, D., tJber die Mosaikkrankheit der Tabakspflanzen. Zeitschr. f. 
Pflanzenkrankh. 1901, p. 1 ff. 

2 Heintzel, Kurt, Kontagiose Pflanzenkrankheiten ohne Mikroben mit beson- 
derer Beriicksichtigung- der Mosaikl^rankheit der Tabaksblatter. Inaug -Dissert. 
Erlangen 1900. 

3 T.oc. cit. D. 274. 

4 Koning, C. J., Die Flecken- oder Mosaikkrankheit . des hollandischen Tabaks 
Zeitschr. f. Pflanzenkrankh. 1899, p. 65. 



68; 

retained in the advancing development of the tissue. No change can be 
observed at first in the epidermis. It shrivels later, becomes brown and 
dry when the chlorophyll has disorganized in the underlying tissue and the 
cells dr}^ up. 

In extensive plantations the infection of the plants usually takes place 
through contact with the hands of laborers who produce wounds when 
thinning out the plants and otherwise working among them. The touching 
of such places with fingers covered with sap from diseased plants is enough 
to inoculate the majority of the healthy plants. The process has often been 
tested experimentally. In an experiment made especially for this purpose 
in Holland, Koning determined 80 per cent, of disease. 

The disease, moreover, is not restricted to tobacco, for Woods' had 
already reported that he could call forth similar phenomena when pruning 
tomato plants. Hunger^ showed as an example that, in the same plant 
species, difi^erent varieties behaved differently according to their origin. 
He found in direct experiments with the heads of plants in Ruitenzorg that 
all the shoots (lateral shoots) of 50 examples raised from American seeds 
had the mosaic disease. Of 25 plants grown at the same time from German 
seed 9 were diseased. On the other hand, the shoots of the 25 specimens 
raised from Indian seed showed no change. 

In speaking of the cause of this disease, we have already mentioned 
that part of the observers assume the presence of micro-organisms without 
having seen them. Iwanowski, in fact, describes a specific bacterium, but 
Hunger found, in subsequent investigations, that the alleged organism dis- 
appeared from the cell with the use of the chloral hydrate phenol mixture. 
We can, therefore, say that no parasitic organism is known, as yet, for the 
typical mosaic disease, or, rather, the majority of exact observations lead 
to the theory that a physiological disease is concerned here, the transmission 
of which takes place by means of carriers which, advancing in the infected 
organism, cause, in the existing normal group of substances, the same 
changes in the arrangement which produce the disease and in this way the 
spread of the disease. The different degrees of susceptibility of the differ- 
ent varieties — those with thick leaves being much more resistant than those 
with thin leaves — prove that some predisposition must exist. The highly 
prized Deli tobaccos (those with the tenderest leaves) suffer most. The 
influence of cultivation is shown by the fact that virgin soils give decidedly 
smaller percentages of sick plants than those already used repeatedly for 
the cultivation of tobacco (cf. Hunger's field experiments) ^ 

Two points of view are now held by the investigators who do not rec- 
ognize microbes as the cause of the mosaic disease. One group beUeves 
that the plant produces a poison, a virus, which is capable of producing the 
same poisonous substances in the cell content of an inoculated plant, thereby 



1 Woods, A. F., Observations on the Mosaic disease of Tobacco. U. S. Dept. of 
Agriculture, Bull. No. 18, May, 1902. 

2 Loc. cit., p. 287. 

3 Zeitschr. f. Pflanzenkrankh. 1905, p. 289. 



688 

causing the disease. Beijerinck^ appeared first among those who hold this 
opinion. In 1898 he described a "contagium vivum fluidum" as the cause. 

Hunger says further-, "I consider the virus of the mosaic disease to 
be a toxin which is always produced in the tobacco plant during the metabo- 
lism of the cells but, in normal cases, exercises no effect, while it accumu- 
lates when the metabolism is too strongly increased and then causes disturb- 
ances such as the mosaic form of variegated leaves." I assume that the 
toxin of the mosaic disease, which is produced primarily by external stimuli, 
is capable, when penetrating into normal cells, of exercising a physiological 
contact effect with the result that the same toxin is formed there secondar- 
ily. In other words the toxin of the mosaic disease possesses the peculiarity 
of acting as a physiologico-autocatalytic agent. In this way the virus can be 
make its way independently throughout the tobacco plant and, reaching the 
paths leading to the meristem, can exert its influence there on the young 
structures. This explains the capacity of the diseased substance for in- 
crease. "This capacity does not depend on the active reproductivity of the 
virus itself but simplv arises from the passive reproductive power of the 
living cell substances." 

In contrast to the theory of poison we represent a second theory and 
call attention to the experiments of Pantanelli and others who have proved 
a change in the amount and action of the enzymes. HeintzeP says (1899, 
p. 45), "The enzyme which causes the mosaic disease may, therefore, be 
considered an oxydase." Accordingly, the cause of the mosaic disease 
would be present also in a healthy plant and would have an abnormal action 
only under special circumstances. Woods* expresses exactly the same 
theory since he thinks only certain conditions are concerned under which 
the oxidizing enzymes become effective — "cither become more active, or are 
produced in abnormally large quantities." The condition of matters at 
present is still uncertain and forbids a closer examination of the relations. 
For the theory which we advance and have described in the first section of 
this chapter, the question is less important, whether an increase of the 
oxydases actually takes place, or w^hether a decrease of the reducing sub- 
stances, always accompanying the oxydases, whereby the same amount of 
oxydase has an increased activity. Hunger has actually proved that the 
leaf with the mosaic disease contains less reducing and tannic substances 
than do healthy tobacco leaves^. A scantier sugar content has been proved 
in the diseased leaf, corresponding to a lack of chlorophyll; besides this. 



1 Beijerinck, M. W., Over een contagium vivum fluidum als oorzaak van de 
Vlekziekte der tabaksbladen. Koninkl. Akad. van "Wetenschappen te Amsterdam. 
Nov. 1898. Tiber ein Contagium vivum fluidum als Ursache der Fleckenkrankheit 
der Tabaksblatter. Centralbl. f. Bakeriologic 1899, Part II, No. 2, p. 27. 

2 Loc. cit., p. 296. 

3 Heintzel, Kurt, Kontag-iose Pflanzenkrankheit oline Mikroben, mit beson- 
derer Beriiclvsichtig-ung- der Mosailckranl-cheit der Tabaksblatter. Inaug-. -Dissert. 
Erlangen 1900; cit. bv Hunger, loc. cit., p. 269. 

4 Woods, A. F., The destruction of chlorophyll by oxidizing enzymes. Centralbl. 
f. Bakt. 1899. Part II, Vol. V, No. 22, p. 745. 

5 Hunger, P. W. T.. Bemerkungen zur Wood'schen Theorie iiber die Mosaik- 
krankheit des Tabaks. Bull. d. I'lnst. Bot. de Buitenzorg 1903, No. XVII. 



689 

less free organic acids are found^. Accordingly, the parts suffering with 
the mosaic disease lack the ability to form sufficient reserve substances; 
and thus the mosaic disease, which, according to Hunger-, may also be 
transmitted without the existence of any injury, simply by contact with the 
hand, or, in grafting, be transmitted to the stock, belongs under albinism. 

While we still have no reason for restricting the last named phenom- 
enon, because the white variegated plants, in spite of their greater sensitive- 
ness, form desirable specimens for our gardens, yet, the need of earnest 
regulations for combatting the mosaic disease, is most imperative and these 
have often been tried. According to Koning liming the soil has proved to 
be the best method. Hunger also proved good results by fertilizing with 
bone meal and gives warning primarily against an excessive chemical ferti- 
lization. In my opinion the disease is a result of inbreeding, which can be 
overcome successfully by decreasing the supply of nitrogen and by increas- 
ing the lime. 

Wood says^, "Overfeeding with nitrogen favors the development of 
the disease and there is some evidence that excess of nitrates in the cells 
may cause the excessive development of the ferments causing the disease." 

The choice of seed also deserves especial attention as is evident from 
the statements of Bouygeres and Perreau*. These investigators took seed 
from plants, in the midst of a diseased field, which up to the time of har- 
vesting had remained free from the mosaic disease. They obtained 98 per 
cent, of healthy plants. These were, at any rate, capable of being infected 
in wounds brought in contact with parts having the disease. Special con- 
sideration should be given primarily to the soil. In earth, on which tobacco 
had been grown for some time, healthy seed very easily became diseased". 

Pox OF Tobacco. 

A\'e have mentioned already, in discussing the mosaic disease, that other 
phenomena of discoloration have often given rise to much confusion. An 
example of the latter is furnished by the pox disease. Iwanowski and 
Poloftzoft'" have called attention to the difference between this and the 
mosaic disease. For three years they studied this disease in Bessarabia, 
having been commissioned by the Russian Department of Agriculture- 
According to Hunger", the disease manifests itself in the appearance of 



1 Hunger, De Mozaik-Ziekte bij Deli-Tabak. Deel I. Mededeelingen uit S'Lands 
Plantentuin LXIII, Batavia 1902. 

2 Hunger, On the spreading- of the Mosaik-disease (Calico) on a tobacco field. 
Extr. Bull. d. I'Institut Bot. de Buitenzorg 1903, No. XVII. 

3 Observations on the mosaic disease of tobacco, Washing'ton 1902, p. 24. 

4 Bouygeres et Perreau, Contributions a I'etude de la nielle des feuilles du 
tobac. Compt. rend. 1904, CXXXIX, p. 309. 

5 Behrens, J., Weitere Beitrage zur Kenntnis der Tabakspflanze. Landwirtsch. 
Versuchsstat. 1899, p. 214 ff and 482 ff. 

<5 Iwanowski und Poloftzoff, Die Pockenkrankheit der Tabakspflanzen. Mem 
de I'Acad. Imp. de St. Petersbourg 1890, ser. VII v. XXXVII. 

7 Hunger, Zeitschr. f. Pflanzenkrankh. 1905, p. 297. Here also pertinent 
bibliography. 



690 

numerous small white specks at times of great drought, while in Deli the 
mosaic disease is observable immediately after sharp rainstorms. The 
cause is looked for in conditions similar to those in the mosaic disease. 

White Rust of Tobacco. 
A further phenomenon has been confused with the mosaic disease 
which is called "White Rust." Delacroix^ has called attention to the fact 
that, in this the mature leaves, and not the young ones, become sick first. 
The spots are more numerous but are smaller and stand out in sharp relief. 
Ultimately they are bounded by a cork layer. The cause is said to be 
a micro-organism, Bacillus macidicola. 

The Disease of the Peanut in German-East Africa. 
According to Karosek- Arachis hypogaea, one of the most important 
cultivated plants of the East African colony, is in general but little attacked 
by disease. In the neighborhood of Tanga and Lindi, however, a phenom- 
enon has now appeared to a considerable extent which recalls the mosaic 
disease. The leaves, blossoms and fruit remain small, the yield is scanty; 
whitish, irregular spots appear on the lea^'es, deforming them somewhat. 
The leaves finally become brown and die. Fungi have been found and any 
lack of nutrition is out of the question. 

The Shrivelling Disease of the Mulberry. 

This disease, at present widely distributed through Japan, which surely 
will be found later in Europe, has only been observed more exactly for 
possibly the last twenty or thirty )^ears and has been studied earnestly only 
during the last ten years. According to Suzuki^ whose description of the 
disease we follow, it is called Jshikubyo or Shikicyobyo in Japan. Like the 
mosaic disease, this shrivelling disease also occurs most extensively in the 
tender leaved and quick growing varieties. Within the same cultural 
varieties the individuals suffer most strongly which receive too much liquid 
fertilizer, while trees planted in poor soil, or in mountainous regions, are 
almost free from it. 

The fact that the disease became noticeable at about the time when 
the so-called "pruning method" was universally introduced into Japan is of 
especial importance. This method consists in the cutting down of the 
trunks, or branches, at the time of the most luxuriant leaf development 
(May to June), close to the soil when the plant is three years old. The 
stock at once produces new, luxuriant shoots which by September have 
become 5 io 6 feet tall. These branches, in the following summer, are cut 
back again, either close to the soil or several feet above the surface. Speci- 
mens, which have been cut back for a long time, suffer less from the disease 

1 Delacroix, G., La rouille blanche du tabac et la nielle, eta Compt. rend. 
1905, CXL, p. 675. 

2 Karosak, A., Eine neue Krankheit der Erdniisse in Deutsch-Ostafrika. 
Gartenflora 1904, p. 611. 

3 Suzuki, U., Chemische und physiologrische Studien iiber die Schrumpfkrank- 
heit des Maulbeerbaumes, eine in Japan sehr welt verbreitete Krankheit. Zeitschr. 
f. Pflanzenkrankh. 1902, p. 203. 



691 

and it is absolutely unknown in regions where the plants, under the old 
cultural method, have not been cut at all. Consequently, we may maintain 
with certainty that a phenomenon resulting from intensive cultivation is 
concerned here. The fact that the plants remain healthy, which were cut 
back in autumn or the early spring before the opening of the leaves, favors 
the theor}' that this cutting during the time of making growth is the cause 
of the shrivelling disease. Diseased plants can be cured if left unpruned 
for several years. 

The first indication of the disease appears generally when the young 
branches, breaking out from the stump of the trunk, have reached a height 
of one foot. First of all, the uppermost surfaces shrivel or show other 
phenomena of weakness. This change advances gradually do\\'nvvard, 
while the leaves turn yellowish or dark green, or even can retain their 
normal color. This usually sets in slowly since, in the first year, only the 
upper leaves of some shoots become diseased. In the course of time, the 
condition so spreads that the tree dies. There are, however, also acute 
cases in which all the leaves shrivel at the same time in one year. The 
branches of the diseased plants are usually very thin and develop very 
numerous side branches and leaves ; they droop at times and lose their stiff- 
ness. The roots begin to decay. 

Naturally, parasites have often been held responsible for this disease 
and the phenomenon has been declared to be the result of a parasitic decay 
of the roots but the roots are demonstrably healthy in the first stages of the 
disease of the aerial parts ; besides this, it seems very remarkable that a 
parasite always seeks only the trees treated with the pruning method. 

With due consideration of the preceding facts, one is forced to the con- 
clusion that a continued disturbance of equilibrium in the nutritive processes 
must be the cause here. This is confirmed b)^ Suzuki's numerous analyses. 
He found, for example, in the average from ten, experiments that in leaves 
of plants suffering from the shrivelling disease, when the content of the 
healthy leaves is set at 100, the water content is 94.7 per cent. ; the dry 
substance 116 per cent. In 100 parts dry substance the content is : — 

(normally valued at 100) 

Protein 81.8 per cent. 

Fat 86 

Raw fibre 81.4 " 

Extractive substances free from nitrogen 120 " 

Pure ash 91 " 

Total nitrogen 81.8 " 

Albuminoid nitrogen 86.8 " 

Non-albuminoid nitrogen 66.6 

In 100 parts ash content. 

(normally valued at 100) 

Si O, I t3-i per cent. Kg O 92.3 per cent. 

SO," 97.2 " CaO 105.5 " 

Po O, 101.6 " MgO 120.6 •' 



692 

Therefore, a greater abundance of ash in proportion to the organic 
substances produced, as has been emphasized already as typical for all 
defective plants. 

The characteristic of the shrivelling disease of the mulberry is a con- 
gestion of starch in the diseased leaves and a very scanty development of 
the wood body, especially of the conducting elements, the sieve tubes. Be- 
cause of the scanty number and small breadth of the lumina of these 
elements, only a very slow transportation of the assimilated material (here 
especially sugar) can take place. Consequently the continued dissolution 
of the starch is prevented\ Besides these anatomical conditions, chemistry 
now proves the presence of an abnormally large quantity of oxydases and 
peroxydases. According to Woods, it is very probable that the oxydases 
not only destroy all the chlorophyll but also prevent diastatic and proteo- 
lytic action. On this account, they might be the cause of the delay in the 
transportation of the starch and nitrogen compounds. At any rate, Shibata- 
maintains, as a result of his experiments, that the diastase action is not pre- 
vented by the oxydase and that a further production of the enzymes would 
be caused by the entire elimination of the elaborated materials. Later 
experiments must make clear which of these theories is correct. The fact 
is sufficient for us here that the whole amount of the reserve substances is 
exhausted in the sick plants^. This is shown also in the scanty filling with 
starch of the bark on the branches and roots and of the dormant buds, and 
manifests itself also in the decrease of root pressure and the transpiratory 
intensity (Miyoshi). It is now clear that if a plant is continually forced to 
use its reserve material by the removal of its foliage, it does not have time 
enough to mature the new growth, i. e., to deposit sufficient starch, albumen 
and cellulose in these organs. 

The curing of this disease will lie in a return to the normal fall pruning. 
As soon as branches of diseased plants have developed their own roots by 
layering, they develop normally as Suzuki has shown experimentally. 

■ Besides this, very similar phenomena of disease also occur in the tea 
plant as soon as the picking of the leaves is carried on irrationally. 

The Sereh Disease of the Sugar Cane. 

At present the Sereh disease, which appeared in Java in the 8o's of the 
last century and is advancing from the West to the East, is, indeed, the 
most greatly dreaded disease of the sugar cane. It has now been observed 
also in Reunion, Sumatra, Borneo, Malakka, the Mascarrean Islands, and 
in Australia*. According to Kruger^, whom we follow first of all, the name 

1 Miyoshi, M., Untersuchung-en iiber Schrumpfkrankheit ("Ishikubyo") des 
Maulbeerbaumes. II. Journ. Coll. Sc. Tokio 1901, Vol. XV. 

2 Shibata, K., Die Enzymbildung in schrumpkranken Maulbeerbaumen The 
Botanical Magazine XVII, 1903. 

3 Suzuki, loc. cit., p. 277. 

4 Cit. Zeitschr. f. Pflanzenkrankh. 1901, p. 297. 

5 Kriiger, W., tjber Krankheiten u. Peinde des Zuckerrohrs. Ber. d. Versuchs- 
station f. Zuckerrohr in West -Java, Kag-ok-Tegal. Dresden, Schonf eld's Verlag 
1890, p. 126. 



PART IX. 



MANUAL 



OF 



Plant Diseases 



BY 



PROF. DR. PAUL SORAUER 



Third Edition— Prof. Dr. Sorauer 

In Collaboration with 

Prof. Dr. G. Lindau And Dr. L. Reh 

Private Docent at the University Aasistant in the Museum of Natural History 

of Berlin in Hamburg 



TRANSLATED BY FRANCES DORRANGE 



Volume I 
NON-PARASITIC DISEASES 

BY 

PROF. DR. PAUL SORAUER 

BERLIN 



WITH 208 ILLUSTRATIONS IN THE TEXT 



S'&l? 






Copyrighted, 1920 

By 

FRANCES DORRANCE 



©CU570990 

THE RECORD PRESS 
Wilkes-Barrg, Pa. 



m -6 ^9^^ 



693 

originates from the Javanese name for Andropoijon Schociiantliits (Jav. 
Sereh), grown extensively in gardens there. This grass forms unusually 
greatly branched bushes. In its most highly developed form the disease of 
the sugar cane also appears in an excessive formation of short lateral shoots 
which make the plant look bushy. The root system is poorly developed and 
only slender roots spread out in the soil; the majority remain short and 
bushy, for their tips die and those formed anew fall \ictim to the same fate. 
Many parasites are found in the dead tissue ; among these, Tylenchus Sac- 
chari Soltw. is the most common in Java. The internodes of the stem 
remain short; the eyes of the leaf axils swell ui) round, while, in the normal 
cane (with the exception of a few varieties) they lie flat like a shell in the 
small depressions on the stem. The growth of the main shoot is sup- 
pressed and, on this account, the lower eyes, especially those below ground, 
develop c]uickly. In the new shoots, however, the same process of sup- 
pression of the apical growth is repeated immediately as well as that of the 
breaking of the secondary axes. In this way the whole plant gets an obnor- 
mally bushy formation. The Javanese material, which I ordered for inves- 
tigation, at times showed such a ramification of the lateral axes on the 
upper, higher parts of the stem that groups, resembling witches' brooms, 
were formed. All possiltle transitions between this bushy dwarfing and the 
slender normal condition are found in the different stages of the disease. 

As a result of the great shortening of the internodes, the leaves stand 
close to one another like fans. The leaf sheaths seem to enclose each other. 
In many cases, their death does not take place as it does normally by 
advancing from the edge towards the mid-rib, but conversely, and the result 
is that they remain for a long time on the stem and form nests for micro- 
organisms. Their color is usually darker than that of the normally dead 
leaves and while the latter are tough, the abnormal ones are more brittle 
and disintegrate easily. The intensive red colored vascular bundles are at 
once conspicuous in a cross-section through a node of the diseased cane. 
This coloring matter may be withdrawn with alcohol. The cell walls are 
frequently swollen out of shape and partially destroyed. 

This red coloring of the bundles occurs in cuttings and in older plants 
in the first stages, of the disease, so that it was thought that they should be 
emphasized as a characteristic especially deserving of consideration. 

We liave observed this red coloring of the cell walls in many non- 
parasitic diseases of monocotyledons, and Busse^ has been able to produce 
it artificially in the sorghum millet in German East Africa by painting the 
leaf blades with vaseline or paraffme oil. The color spread still further in 
the xylem parts of the vascular bundles and was traced by Busse to a dis- 
turbance in the respiratory process. We consider the red color to be a 
phenomenon of oxidation which indicates a functional disturbance in the con- 



1 Busse, Walter, Unler-suchungen liljer die Krankheilen der Sorghum -Hirse. 
Arb. d. Biol. .\bt. f. Land- u. Forstw. am Kaiserl. Gesundheitsamte 1904, Vol. IV, 
Part 4, p. 319. 



694 

ductive system due to very different causes but especially frequent in root 
diseases. It appears also very clearly in the pineapple disease, in a parasitic 
disease of the sugar cane produced by Thielaviopsis ethoceticus which can 
be transmitted by cuttings. The greater the amount of sugar in the stem — 
this increases constantly from the base up to about the middle of the stem — 
the more easily the cuttings become diseased by the fungi ^ The red color 
appears in the Sereh disease at times isolated in some nodes, while the fibro- 
vascular cords of the underlying internodes are still uncolored. It may be 
concluded from this that the disease represents a general ailment, a constitu- 
tional disease, which shows its first visible symptoms in especially weakened 
places. 

The cause of the disease has been sought in all kinds of influences ; 
exhaustion of the soil, degeneration due to continual asexual propagation, 
abnormal atmospheric conditions, unsuitable fertilization, especially with 
peanut meal (Bungkil), too deep planting, or too high covering with earth, 
too early, or too late planting, and finally parasites. Among the latter, 
nematodes, fungi and bacteria come under consideration. 

The conclusions of one scientist contradict those of another. Thus, 
for example, Kruger states that he has found bacteria in the ducts as a 
constant accompaniment of the disease, while Tschirch- considers it impos- 
sible that bacteria can be the cause of the disease and sees the initial stages 
in an injury to the roots. Benecke^ sides with Kriiger, Mobius* opposes the 
assertion of any existing degeneration and also seeks the cause in parasitic 
organisms. OhP perceives the cause of the Sereh disease and the disease 
of the coflFee tree in Java, in which the leaves fall, to be the deforestration of 
the mountains and subsequent drought. Janse*, in the same way, traces the 
disease to a lack of water, since he thinks that the gummy obstruction of 
the ducts prevents conductivity. He connects the formation of the gummy 
substance with bacteria (Bacillus Sacchari). Went'' considers the Sereh 
directly as a gummosis which arises from the co-operation of a parasitic 
root and leaf sheath disease and which may be propagated by cuttings. 

Wakker^ considers the disease as a non-parasitic gummosis, associated 
with the excess of water which cuttings, developing during the dry monsoon, 
suffer in the following rainy period. 



1 Cobb, N. A.; Fung-US Maladies of the Sugar Cane. Rep. Exp. Stat, of the 
Hawaiian Sugar Planters' Association. Bull. 5, Honolulu, 1906, Part 1, p. 218. 

2 Tschirch, A., Uber Sereh, die wichtigste aller Krankheiten des Zuckerrohres 
in Java. Schweiz. Wochenschrift f. Pfarmazie 1891. 

3 Benecke, Franz, Proefnemingen ter Bestrijding der "Sereh." Samarang 1890. 
For further treatises by this author cf. Zeitschr. f. Pflanzenkr. 1891, p. 354, 361. 

4 Mobius, M., Over de gevolgen van voortdurende vermenlgvuldiging der 
Phanerogamen langs geslachteloosen weg. Mededeelingen van het Proefstation 
"Midden Java" te Samarang. 1890. 

s Ohl, A. E., Eene Waterstudie. Batavia 1891; cit. Zeitschr. f. Pflanzenkrankh. 
Vol. I, p. 365. 

6 Cit. Zeitschr. f. Pflanzenkrankh. 1893, p. 238. 

7 Went, F. A., Die Serehkrankheit; cit. Zeitschr. f. Pflanzenkrankh. 1894, p. 
235 and 1901, p. 297. 

8 Wakker, J. H., De Sereh-Ziekte S. A. Archief voor de Java-Suikerindustric. 
1897, Afl. 3. 



695 

Thus the difiference of opinion extends to the most recent times^ with- 
out having led to any positive reconciUation. The reason probably lies in 
the fact that the characteristics given for the Sereli disease also occur in 
other diseases, as will be shown, for example, in the following section, and 
thus different investigators may have considered different forms of the 
disease. 

We will emphasize a few facts from positive results, i. e. that healthy 
cane can remain healthy in plantations suffering from the Sereh disease, and 
that diseased cane remains diseased in healthy fields. It should be added 
further that often wide bands along the edges of the fields appear diseased 
first, or only the edges themselves, and that the Cheribon cane, which tends 
to disease when planted in mountainous regions, has given healthy cuttings. 
Some cuttings are practically immune, while others are susceptible. Even 
the cuttings of the same variety from regions free from the Sereh disease 
at first remain healthy, even in infected regions. It is evident from this that 
the disease can scarcely be parasitic but falls under the group of the gum- 
moses. It can, therefore, not be contested that the bacterial gummosis 
conditions exist in the Sereh disease, just as in the rot of our sugar beets, but 
these forms also depend upon certain conditions of weakness of the plant 
body which we call displacement of the enzymatic functions. 

We consider the causes of the insufficient ripening of the cane, i. e. 
non-deposit of reserve substances, cane sugar in this case, to be the inconsid- 
erate cultivation of sugar cane with an increased supply of fertilizer and 
water on heavy soil in enclosed positions, etc. Actually, the loss in the 
sugar content is uncommonly great in the Sereh disease. 

We are not in a position to determine the process which causes the lack 
of reserve substance. It is, however, a matter of indifference in judging of 
the disease, whether an excess of destructive enzymes is present or a para- 
lyzation of the constructive ones. The metabolic processes, leading to this 
lack of cane sugar, are naturally present in the whole plant no matter where 
they make themselves felt symptomatically. Therefore, each smallest part 
of the diseased cane, even if it shows no symptoms of the Sereh disease, is 
actually predisposecl to it and even contains the carriers of the disease. 
Consequently each Bibit (cutting) from the plant having the Sereh disease 
is condemned to death as soon as it comes under conditions favoring the 
disease. It heals itself, however, and returns to the normal enzymatic 
activity on tracts of land where the Sereh does not break out. 

From this the best method is clearly the choice of varieties immune to 
Sereh or, at least, the cultivation of Bibits in open, mountainous positions 
and other localities which do not permit the disease to occur. Probably a 
change in cultivation takes place in such a way that only weak fertilizing 
and more porous soils, as well as open positions, are used in the cultivation 



1 Hein, A. S. A., Hypothesen en Ervaring- omtrent de Sereh ziekte. De 
Indische Mercuur. Amsterdam 1905; cit. .Tahresber. f. Pflanzenkrankh. v. Hollrung-, 
Vol. VIII. 1906, p. 245. 



696 

of cane; these also cause a standstill in the Sereh disease in distinct centres 
of the disease. 

We believe also that the diseases termed the rusts of sugar cane belong 
here. Of these, we refer here to the Powdery Disease described by Spegaz- 
zini\ which occurs also with red spots and a gummy secretion but becomes 
noticeable because of its unpleasant smell. The base of the stem suffers 
especially. A bacillus (Bacillus sacchari) may be isolated from the gummy 
slime which requires an acid nutrient substratum and produces a protein 
decay which gives rise to the offensive smell of the diseased cane. This 
disease also occurs with Andropogon nutans. Tn regard to the production 
of the red color in the vascular bundles and of the gum in the sugar cane 
by micro-organisms, Grieg Smith's- work is of especial importance. He 
found reddened vascular bundles in otherwise healthy cane as well as in the 
stems which had become gummy because of Bacillus vascularum Cobb. The 
red color was produced by the tilling of the large ducts with a red gum just 
as in the Sereh and other sugar cane diseases. He found further a fungus, 
which produced a shiny, very scarlet color on nutritive media with dextrose 
but no gum, and gum bacteria in the diseased ducts, especially Bacillus 
Pseudarabinus n. sp. Bad. Sacchari ("this variety normally lives in the 
sugar cane") and besides this Bacillus vascularum. On sheets of nutrient 
agar with laevulose, the fungus produces no coloring matter, but in combi- 
nation with Bacillus pseudarabinus a bright scarlet is produced and in com- 
bination with Bad. SaccJiari, a rusty brown. 

It will be seen from these examples how the constitution of the sub- 
stratum is able to modify the parasitic activity and in what way, therefore, 
different aspects of disease are produced. A preliminary condition neces- 
sary for the production of the disease is, however, a deviation from the 
normal metabolic processes in cane, healthy up to that time, which favors 
an increase of bacteria (probably always present) and which appears sooner 
or later in the different susce[)tible varieties of cane but remains suppressed 
in the immune varieties. 

Cobb's Disease oe the Sugar Cane. 

According to Erwin Smith'\, the Sereh disease resembles in many ways 
the disease of the sugar cane occurring in Australia (and especially in 
Maurilis, Java and Brazil), which Cobb describes. This latter disease is 
characterized l)y diminutive growth, shortening of the internodes, albinism, 
premature sj)routing of the buds, and propagation by infected cuttings. It 
differs essentially, however, from the Sereh, since the heart of the cane stalk 
becomes lignilied and masses of 3'ellow slime (gum) occur constantly in the 

1 Spegazzini, La gangrona luimida o polvillo de la canna do zucchero. Rivista 
azucarera 1S95. 

2 Smith 11. Grieg, Sidney. Rakteriolog. Laboratorium der Linnean Soc. of New 
South Wales. Centialbl. 1'. Bakt. usw. 1906. Vol. XV, No 25, p. 733. 

3 Smith, Erwin, Ursache der Cobb'schen Krankheit des Zuckerrohres. Central- 
blatt f. Bakteriologie usw. 1904. Vol. XIII. Part 22, 23. 



697 

blood red bundles of the trunk. It has been proved by careful inoculation 
experiments that the cause of the disease is Pseudomonas {Bacillus Cobb) 
vascularum. 

Smith considers the red coloration of the branches (corresponding to 
the brown coloration of bacterial gummoses) as a reaction of the plant. 
According to Prinsen Geerlings, a neutral uncolored substance, dissolving 
with difficulty, exists in the cellulose of the normal sugar cane, which turns 
yellow with the action of an alkali (like tannin), but becomes red, when 
aerated, and later brown. 

The interesting result is the definite proof that certain varieties of cane 
(common green cane) in inoculation experiments show extraordinarily great 
susceptibility, while other varieties (for example, common purple cane) 
become only slightly diseased. The sap of the latter canes showed approxi- 
mately a doubled acid content and Smith surmises that the high suscepti- 
bility to parasites depends "only on the weak acidity or the minimal occur- 
rence of a specific arresting acid." Cobb reports that where such resistant 
varieties are grown the disease has disappeared. 

To the same group of diseases belongs also the disease of the sugar 
beet which I first described as "bacterial gunimosis" and later as "beet tail 
rot."* So far as can be determined experimentally, the bacteria have an 
epidemic distribution only if continued heat and drought with abundant 
nitrogen fertilization weaken the growth of the beets. If wet weather 
sets in with the same excessive fertilization, the yield in sugar becomes 
considerably less, but the bacterial gummosis is lacking'. 

Peach Yellows. 

Since 1887 a disease of the peaches in the United States of North 
America has been studied very earnestly. It has caused uncommonly great 
injury to extensive orchards. A yellow disease (chlorosis) is concerned 
here which is transmissible by grafting-. This condition of yellow foliage 
differs in this from the similar phenomena caused by a lack of nutrition, 
frosts, etc. In this disease, which has constantly increased in the last 20 
years and has made the cultivation of the peach unprofitable in many places 
(in the Delaware and Chesapeake regions), a peculiar red mottled condition 
and a premature ripening of the fruit are very characteristic. To this 
should be added the premature development of the winter buds and the 
extensive development of latent and adventitious buds ; therefore, a diseased 
branch as in the Sereh disease. Although the fruit, which at times has red 
stripes extending into the flesh, attains a normal size in the first year, it 
becomes smaller in the following years of the disease, and tasteless, or even 
bitter. The phenomenon is restricted at first to a few branches and then 



* See V. 2 of the Manual, p. 42. 

1 Zeitschr. f. Pflanzenkrankh. 1892, p. 2S0. 1896, p. 296, and 1897, p. 66. Blatter 
f. Zuckerrtibenl^au 1894, p. 1. 

~ Smith, E. F., in Report of the chief of the Section of Veg-etable Pathology. 
Washing-ton, 1890. Smith, Erwin F. Additional evidence on the communicability 
of peach yellows and peach rosette. Washington 1891, Bull. 1. 



698 

extends gradually over the whole tree. At the same time the foliage begins 
to turn yellowish green in places and weakly pale shoots break out from the 
bark. The foliage developed in the following spring appears yellow, or a 
reddish green, the new shoots are stunted and their leaves roll and curl. At 
times the tips of all the healthy, slender shoots suddenly show a continually 
repeated formation of lateral axes which become weaker and weaker and 
whole nests of sprouts are produced (usually in the autumn). Death occurs 
sooner or later. In budding with healthy eyes from diseased trees, a large 
percentage of the budded trees seems to be sick and, in fact, not only the 
shoot developed from the eye itself, but also the stock, similar to the varie- 
gation in albinism. 

The rosette, which occurs* also in plums, was considered at first a 
variety of the peach disease here described, but later Smith held it to be a 
specific disease. Its course is uncommonly rapid, so that death occurs in 
the same year, or, at the latest, in the following year. Here, too, the leaf 
rosettes are produced by a strikingly abundant development of latent eyes 
and the development of lateral shoots, which attain, however, scarcely one- 
sixth the length of normal shoots. These may develop other side shoots, 
which again branch. Such nests of branches often contain from 200 to 400 
small leaflets and malformed stipules. At the bases of the shoots the leaves 
are larger and better developed but peculiarly rolled in at the edges and 
strikingly stiff, because of a certain rigidity of the mid-rib. These leaves 
turn yellow in the early summer and drop. In the course of the summer 
the rosettes dry up; the blossoms of the diseased shoots, however, do not 
develop earlier than those of the healthy shoots, but rather somewhat later. 
On the other hand, all the fruits which become gummy fall when still green 
and never show the red specking as in peach yellows. In both diseases the 
fine, lateral roots are found to be shrivelled and dead and the rosette disease 
is often accompanied by abundant gum centres. This rosette disease may 
also be carried to the stock in budding. Only, as a rule, very many more 
normal lateral eyes in a shoot develop into rosettes and, thereby, the bushy 
formation becomes denser than in the peach yellows. 

Opinions as to the cause of this disease are divided, yet the bacterial 
theory has become less prominent since it has been recognized that in many 
cases mycelium and bacteria have not been found. For this reason the 
theory has become much more universal that a constitutional disease is 
concerned here, in which substances due to an abnormal metabolism may 
be transmitted by grafting as in albinism and the mosaic disease. In fact, 
here, the transmission probably takes place through the pollen, for Morse^ 
has observed that out of three varieties of peaches, two became diseased, 
while the third, the white Magdalene, remained healthy. This variety could 
not be crossed with others. 



1 Morse, E. W. On the power of some peach trees to resist the disease called 
"yellows." Bull. Bussey Institution, Cambridge, 1901; cit. Zeitschr. f. Pflanzenkr. 
1902, p. r.8. 



699 

Of the unusually numerous practical experiments made especially by 
Smith^, it can be only stated as a result, that no one has succeeded, as yet, 
in obtaining any indication of the cause. In ordinary years, a lack of nutri- 
tion, or its excess, can not be considered as a reason for the disease. Still it 
may be observed that rainy, cool summers show a decrease of the disease 
and dry periods, an increase. Grafting on the Marianna plum was found 
to be apparently a protection against the rosette disease, since the eyes from 
the diseased peach developed to healthy shoots. Infection experiments with 
about twenty different kinds of bacteria and yeasts, taken from the tissue of 
diseased peaches, gave no other result than a swelling in a few cases at the 
point of infection or an exudation of gum-. 

The almond suffers from both of these diseases and apricots and Japa- 
nese plums from the yellows^. 

In my opinion, injuries are concerned here which are produced by 
intensive cultivation and lack of consideration of the soil requirements of 
the peach. In the long run, all heavy soils, rich in fertilizers, become 
dangerous for the peach. In combatting this disease, it might be well to 
consider primarily cultivation on light soils and in open places. 

GUMMOSIS OF THE ChERRY. 

The exudation of gum is well known as a widespread phenomenon 
especially among the stone fruits and can be produced by very different 
kinds of causes. 

With us, the cherry and the peach suft'er most frequently from gum 
exudations. We sometimes find light yellow, transparent masses, at other 
times browm, cloudy solid ones, extending over a part of the bark of a 
branch or the trunk. These masses are soluble in boiling water; insoluble 
in alcohol and cannot be crystalized. When boiled with dilute sulfuric acid, 
the jam contains a' sugar which can ferment and yields mucic acid when 
treated with nitric acid. They belong, therefore, to that group which 
organic chemistry terms Gums. Different varieties of gums have been dis- 
tinguished, according to their capacity for swelling in water. Gum per- 
fectly soluble in cold water is called Arabin, which has all the characteristics 
of an acid*. The gum tragacanth which swells up in water to a sticky jelly 
is a representative of the Bassorin group, and the modification of Bassorin 
is called Cerasin, which is soluble in boiling water. Cherry and plum gums 
are a mixture of Arabin and Cerasin. We may assume that the gum formed 
in gummosis changes its constitution according to the time of its production 
and the character of the tissues from which it is produced. It may have 
some relationship with pectin substances. Gum arable has the character of 
an organic calcium salt. 



1 Smith, E. F. Experiments with fertilizers, etc.; cit. Zeitschr. f. Pflanzenlvr. 
1S94, p. 177. 

2 Smitli, E. P. Additional notes on peach rosetie. The .Tonrnal of Mycology, 
Vol VII, No. 3, 1893. 

3 Cit. Zeitschr. f. Pflanzenkrankh. 1896, p. 156. 

4 (Jzapek, Fr. Biochemie d. I'flanzen. Jjnipzig, 1905, Vol. I, p. 554. 



We get the best insight into the nature of the disease by considering 
the. young gummed lateral cherry branch ilkistrated in Fig. 155, i and 2. 
Isolated ducts are shown, first of all, in the middle of the normal wood, 
which are entirely filled with gum (Fig. 155 2a). This gum has been 
formed in part from the secondary membranes of the ducts. When treated 
with hydrochloric acid, which colors the walls of the wood cells and ducts a 
brilliant carmine, as well as the bast fibre cells, the breaking down of the still 
red wall of the duct into yellow gum, found here in drops, may be easily 
recognized. This phenomenon is frequently only a forerunner, or accom- 
paniment of a much more extensive formation of gum, whereby large gum 
centres are produced in the wood and in the bark. 

Even in one year old branches, it is possible to discover the first traces 
of the gummy exudation by examining closely cross-sections of young 
branches in which gummosis is recognizable to the naked eye only in the 
occurrence of extremely small black points. Lighter colored places appear 
at times in the wood body which, with more thorough investigation, are 
found to be composed of parenchymatous instead of prosenchymatous cells. 
This abnormal wood parenchyma (Fig. 155 2 p.) is usually enclosed by 
normal wood, which separates it also from the cambium (2c). As a rule, 
these lighter colored places, which are usually deposited side by side, parallel 
to the periphery, and usually separated by thin radial stripes of normal 
wood, are . found in difi'erent developmental stages. Some are perfectly 
unimpaired ; others show cells near the centre which have already changed 
to gum. In the same cases, all the abnormal parenchyma and, in the same 
way, the normal wood, are entirely changed to gum (Fig. 155 2d). In this, 
the intercellular substances are dissolved first of all ; then follow the pri- 
mary, and finally the secondary membranes of the ducts and the wood cells. 
In such large gum holes, a peculiar process of growth of some cells sets in, 
together with the simultaneous dissolution of the remainder. While the 
wood cells and ducts especially undergo gummosis, some medullary ray cells 
at first grow longer. The starch which they contain is dissolved ; in a few, 
two new cells may be observed, which elongate in different directions. The 
medullary ray cells, lying more toward the centre and somewhat removed 
from the gum centre, round off and sometimes elongate. In this w^ay arise 
many celled filaments, which remind one of certain algae (Trentepohlia) 
(Fig. 155 m) and which grow freely into the gummy mass. They are 
also dissolyed, beginning at the outside, but this does not take place in any 
definite order. Often the cells at the tip of the filament are found dissolved, 
with the exception of a thin remnant of the walls. In other cases the cells 
at the base are dissolved and then the piece of the filament, which has become 
free, lies isolated in the gummy mass. 

Very similar processes are found in the bark, the thin walled bast cells 
of which (Fig. 155 b) very easily succumb to gummosis. The gum centres 
are met with much more frequently in the bark than in the wood. In rare 







Fig-. 155. Veai-i)l(] twig- of .sweet cherry with mature gum cavity and parenchy- 
matous ti.ssue aggregations in the healthy wood. 



702 

cases I have found the initial stages only in the cambium itself and, in fact, 
more frequently in the peach than in the cherry. 

However, where the initial stages can be found, the evil is always 
dangerous because it spreads further. Gummosis produced in the wood soon 
spreads to the cambium and the bark, when it becomes very extensive in the 
bark, and thus may furnish the greatest part of the gum on the exterior of 
the trunk; the cambium also does not escape later. The assertion that 
gummosis always begins in the cambium is correct only if by cambium is 
meant the primordia of imperfectly developed cells which later fall victim 
to liquefication. The profess of liquefication itself can begin at any place in 
the branch and long after the formation of these tissues has taken place. 
On this account, we find gum holes in the middle of the wood body. 

The ultimate result is essentially the same. At some point in the cir- 
cumference of the trunk, the cambium is finally destroyed and the already 
matured wood becomes more or less diseased. A wound thus appears 
which spreads further and further. This, however, is not always recog- 
nizable externally, for the diseased place is not indicated by gum which has 
exuded to the outside. The gum comes to the surface rarely, or only very 
late, if the cambium is first attacked by gummosis. Then the solid, already 
matured wood dies slowly and, in fact, gradually more toward the centre of 
the trunk, i. e. toward the pith (Fig. 155 2k) than toward the circumfer- 
ence. This arises from efforts at localization, which occur simultaneously 
with the disease. A case illustrated in the drawing (Fig. 155 i g) and 
occurring not infrequently, consists in the drying up of the bark above the 
affected wood, with the exception of a few bast bundles, and not its dissolu- 
tion. At that place, the part marked W in the figure is bridged over by 
bark elements (Fig. 2 r). The formation of gum is not very extensive but 
the attempt of the tree to heal the wound becomes more noticeable. This is 
perceptible in one-year-old branches. Figure 155 /, illustrating a gnm 
pocket a year old, shows at u the attempt of the tree to overgrow the place 
(during several years) : a indicates a branch. 

A more abundant formation of wood and bark on the healthy part of 
the trunk, lying next to the wound (Fig. 155 2 h) makes the trunk thicker 
on the wounded side than on the healthy side (1') and above and below the 
wound. If the bark is retained above the wound the edges of the over- 
growth (Fig. 155 u) have raised the dry bark from the dead wood and in 
this way a cavity forms of which the back wall is formed from the wood 
and pith partially attacked by gummosis and the front wall by the dry bark 
(not drawn in the figure) and the sides of the freshly formed callus {u u). 
The cavity thus produced is a lodging place for insects and fungi. 

The newly formed callus, however, rarely remains intact. In the 
majority of cases, small gum centres (Fig. 155 2d') are found in the lux- 
uriantly developed new tissues. To be sure, the living bark attempts to 
enclose tlie diseased places l)y layers of cork, but I have never been able to 



703 

find a case of healing. The difficulty in closing the wound is explained by 
the presence of new gum centres in the callus. 

We have the following points to emphasize from the consideration of 
the cherry branch afifected by gummosis here illustrated, i. The pro- 
duction of parenchymatous tissue groups between the prosenchymatous 
elements of the wood. 2. The position of the groups between two medul- 
lary rays which can curve about the parenchyma aggregations, and, more 
rarely, are able to participate in their formation. 3. The production of 
these groups independently of wounds. 4. The liquefaction of these tissue 
aggregations into gum pockets into which the resistant medullary ray cells 
grow like threads. The last circumstance is explained by the fact that in the 
same cambial ring zone of the branch, or trunk, the medullary cells develop 
more rapidly than the tissue lying between them, and, therefore, are elon- 
gated further radially into the bark body where they function as parenchy- 
matous tissue. At the time when the process of liquefaction begins, the 
medullary ray cells, therefore, are tougher and more resistant and the first 
gummy centres appear as holes between two medullary rays when the 
gummosis is not caused by wounds. 

The more recent experiments attempting to explain the production of 
gum exudation^ begin with the phenomena of injury. Beijerinck and Rant- 
assert in their very thorough work that the gummy exudation depends "on 
the abnormal development of the embryonic wood tissue caused by the 
wound stimulus." 

Beijerinck presents the subject thus: the normal plant forms cytolytic 
substances w^hich take part in the formation of ducts and tracheids. The 
physiological gum, thus produced, is in fact usually entirely re-absorbed, yet, 
under certain circumstances, it remains demonstrable as such even in the 
cavities of the mature ducts. The "gummy exudation, therefore, depends 
upon an abnormal increase of the action of those cytolytic substances under 
the influence of dying cells, perhaps because an especially large number of 
these are produced in necrobiosis. By necrobiosis is meant the cell activity 
after the death of the protoplasm, while the enzyme bodies remain active." 

Ruhland^ opposes this theory. He calls attention first of all to the fact 
that gummosis can take place in seeds, fruits^, leaves and also in the 
phellogen, on which last point he lays especial stress. He found considerable 
masses of gum in the youngest phellogen of Primus Cerasus and thinks that 



1 Compare the second edition of this manual for older points of view. 

- Beijerinck, M. W., and Rant, A. Wundreiz, Parasitimus and Gummifluss bet 
den Amygdalaccen. Centralbl. f. Bakteriol. iisw. 1905, XV, No. 12. Rant. A. Die 
Gummosis der Amygdalaceen. Dissertation, Amsterdam, 1906. 

3 Ruhland, W. Zur Physiologie der Gummibildung- bei den Amygdalaceen. Ber. 
d. Deutsch. Bot. Ges. 1907, Vol. XXV, p. 302. 

* The g-um exudation appears especially frequently in Plums in wet years. As a 
rule, it forms in little drops of gum as clear as water which come from wounds in the 
fruit flesh made by insects. Often no insect injury can be recognized, and then the 
places bearing the drops are usually harder and somewhat flattened. A considerable 
accumulation of gum is found in the fruit itself beneath these flattened places. I 
also found gummification of the pits of plums along the line of union of the halves, 
so that under slight pressure the two fell apart. 



704 

"a universal peculiarity of embryonic cells is concerned in this gummy disso- 
lution which, however, does not extend so far as dissolution in normal life, 
but only when caused by some further impetus." Ruhland investigated the 
abnormal tissue groups, which may be observed in the production of the gum 
canal and found cells enlarged to vesicles with two fully developed nuclei 
but without the formation of any cell wall between them. The process is 
explained by the adjacent Fig. 156, 

Therefore, the cell filaments, which extend into the gum centre, are 
produced by the "repeated divisions of a cell which, not diseased, lies at the 
base of the filament, while the daughter cells, thus produced, only increase in 
size without division." The normal process of wall formation is arrested 
in the embryonic cell and the carbo-hydrates, designed for the formation of 
cross walls, are transformed into gum substances. The reason for the 
change may be sought in the fact that, because of some injury, the embryonic 




Fig. 156. Section.s through gum -forming- tissue (fixed with chrom-acetate, stained 
with safranin-gentian- violet orange. (After Ruliland.) 

A a cell filament. B a young gum center : at a and /} cells with two nuclei. 

tissues are made accessible to the oxygen of the air; the carbo-hydrates, 
really destined for cross-wall formation, will then pass over into the gum 
which is richer in oxygen. Griiss^ explains the oxidation by means of 
oxygen carriers which are formed in the tissue during growth. Wiesner- 
had earlier assumed a ferment which, like diastase, turns the guaiac emul- 
sion blue and is destroyed by boiling. When treated with Orcin or hydro- 
chloric acid, a red or violet color appears after a short boiling, and a blue 
precipitate forms. In the initial stage of gummosis, only the contents of the 
parenchyma cells are found to discolor in this way, from which it may be 
concluded that the^ ferment has its seat in the protoplasm. The ferment has 
been proved in the gums of seed and of stone fruit trees, in gum arable and 
other kinds of gum. Ruhland's experiments with the removal of oxygen. 



1 Gruss, tjtaer Losung- u. Bildung d. aus Hemicellulose bestehenden Zellwande 
und ihre Beziehung zur Gummosis. Bibl. hot Heft 39, Stuttgart 1896, Erwin Naegele. 

2 Wiesner, tjber ein I-'orment, welches in der Pflanze die Umwandlung der 
Cellulose in Gummi und Schlcim bewirkt. Bot. Zeit. 1SS5, No. 37. 



705 

in which production of the gum centres was suppressed, sliow that a supply 
of oxygen seems to be an absohite necessity. 

In our opinion, the necrobiosis theory of Beijerinck and Rant is unten- 
able, since gummosis may be found without any previous presence of dead 
cells in very young branches and one-year-old seedlings in places which 
represent still intact cell centres such as in Fig. 155 2 p. Therefore, the 
wound stimulus does not enter into the (juestion here. W'e believe rather 
that all embryonic and mature cells are capable of forming gum as soon as 
certain processes of cell wall formation, or maturation, are suppressed. This, 
prevention of the normal maturing of the cell wall can be caused very well 
by an increased supply of oxygen. This oxygen, however, can be directly 
atmospheric oxygen only in case of' injury, but probably is only rarely 
actually such, being furnished rather by substances which carry oxygen as 
Griiss explains. Substances of this kind are present in the normal (jruwth 
of trees. In an exudation of gum only an abnormal increase in the amount, 
or the length of action of these substances is involved\ This increase can 
take place because of wound stimulus. It can also be produced by different 
[)arasites and, finally, developed l)y inorganic poisons. In the latter connec- 
tion, I would mention my experiments in introducing a weak oxalic acid 
solution under the bark of perfectly healthy cherry trees. In the course of 
the summer profuse streams of gum were produced which gradually ceased 
l)ecause of the dying out of the oxalic acid action and they did not continue, 
for example, in wounds which had received only distilled water instead of 
the oxalic acid. 

In regard to the manner in which gum exudations can develop we will 
take as a basis the theories formulated by Griiss'-. 

In his investigations, this scientist has come to the conclusion that the 
hemi-celluloses, Mannan, Galactan and Araban are deposited directly, or 
indirectly, as reserve substances. This takes place directly in the form of 
thickened cell walls in the endosperm of the seed (Phoenix, Phytelephas), 
or in the form of secondary thickening layers in libriform or wood paren- 
chyma cells (different varieties of Astragalus, Prunus, Acacia, etc). They 
can be considered as indirect reserve substances if they compose the cell 
walls of cells containing starch, such as those in the endosperm of the 
Gramineae. The hemi-celluloses, Galactan and Araban, are changed l)y 
enzymes into the gums Galactin and Arabin and can migrate in the tissue 
even before they have been transformed into the sugars galactose and 
arabinose. 



1 These substances arc found in varying amounts in tlie tree accordinK' to tlie 
individual, the place of growth, the time of year, etc. This explains also the different 
results when the sum exudation is produced by injuries. Thus, for example, the 
youngest tips of the branches are not the ones most endangered in this, but- the 
region in wliich the tissue elongates most, i. e. the region beneath the apex. In 
vpgard to the influence of the different sides of the tree and the seasons, I found in 
incisions made monthly that the late spring and the southern to western sides of the 
tree are most favorable for the development of g-imimosis. 

- Loc. cit. 



7o6 

The oxygen carriers, which form gums, are now actually denionslrable 
as enzymes which are produced in the sprouting of the buds and, in fact, are 
present even before the diastase. The latter will then dissolve the hemi- 
cellulose, or other gums, as Griiss has proved for tragacanth. 

If such enzymes are produced in excess or their anti-bodies develop in 
too small amounts, they hinder the normal development of the cell wall in 
embryonic cells, or begin the process of liquefaction in the complete cell of 
the mature wood, so that pathological gum centres are produced. 

It is not at all improbable that an excess of oxalic acid, like the hydro- 
lyzing sulfuric acid and other mineral acids, acts like the naturally formed 
ferments and produces thereby an exudation of gum. Such an increase of 
oxalic acid action can either be brought about by its more abundant forma- 
tion, or through its lesser combination with calcium. Thus, for example, 
Mikosch^ calls attention to the fact that almost no calcium oxalate crystals 
are found in the tissues involved in this transformation. It is evident from 
Benecke's works" that the content of these crystals depends upon the nutri- 
tion. He found in his cultures that the addition of nitrates favors the 
formation of calcium oxalate; that feeding with ammonia decreases this 
formation. 

Among the parasites producing an exudation of gum, Clasterosporiiim 
carpophilum (Lev.) Aderh. (C oryneum Beijerinckii Oud.) should be named 
first of all. Nevertheless, a certain predisposition of the organ is necessary 
if the fungus should become effective. Aderhold^ found in his inoculation 
experiments with leaves that red fungous spots occur without the formation 
of gums as, conversely, wounds with an abundant formation of gum could be 
found in the midribs of the leaves and in the cambium of branches in which 
the fungus was absent. The other parasites behave similarly ; Cytospora leu- 
costoma; Monilia fructigena and M. cinerea, Botrytis cinerea and many 
kinds of bacteria*. 

It is very possible that, in some of the parasites here named, oxalic acid 
is the poison produced by them which causes gummosis. 

Before we take up the question of overcoming exudations of gum, it is 
necessary to turn our attention to the conditions under which the disease 
appears. Duhamel's theory is found most frequently confirmed in pomo- 
logical literature. He thinks that cherry trees, which are planted in too 
strong soil, are most subject to the disease. We find this proved especially 
with the peach and cherry if clayey soil is understood by the term "strong 
soil." Exudations of gum are found less frequently on warm, porous soils 
which can be very rich. Further, we find exudations of gum abounding in 



1 Mikosch, K. Untersuchungren iiber die Entstehung- des Kirschgummi. Sitz- 
ungsber. d. Akad. d. Wiss. Wien; cit. Bot. Centralbl. 1907, XXVIII, No. 27. 

- Benecke, W. tJber Oxalsaurebildung- in griinen Pflanzen. Bot. Zeit. 1903, Vol. 
J^X'l. cit. Bot. Centralbl. (Lotsy) 1903, No. 27, p. 16. 

3 Aderhold, R. tJber Clasterosporium carpophilum (Lev.) Aderh. und die 
Beziehungen desselben zum Gummifluss des Steinobstes. Arb. d. Biol. Abt. d. Kais. 
Gesundheitsamtes 1902, Vol. II, Part 5. 

4 Ruhland, W. tJber Arabinbildung durch Bakterien und deren Beziehung zum 
Gummi der Amygdalaceen. Ber. d. Deutsch. Bot. Ges. 1906, Part 7. 



70/ 

larger, unclosed wounds on the branches. In the same way, we find them 
occurring in specially young peach branches, of which the bark has been 
greatly injured by bruising or rubbing. 

In my experiments, in which all the eyes were removed in the spring 
from a considerable number of cherry trees, an exudation of gum occurred 
with very few exceptions. In other experiments, in which the trunks had 
been peeled for a considerable distance, gummosis appeared in the bark near 
the upper girdling cuts, in which no new structures in the forms of callus 
had been formed. Finally, it is well known that great injury to the roots, 
or crown, in transplanting, as well as poor grafting, can give rise to the 
formation of gum. 

All these injuries, in my opinion, do not act through necrobiosis but 
because of a simple wound stimulus which causes an excessive current of 
constructive materials to a spot where they cannot find normal utilization. 
There sets in at the same time, a hastened, new formation of cells, which 
becomes evident in the formation of the primordia of parenchymatous ele- 
ments instead of prosenchymatous cells, as in all other processes of wound 
healing. Therefore, the activity of the new cell formation becomes excess- 
ively favored at a time when the constructive enzymes already prevail and 
wall-thickening as well as a deposition of reserve substances should begin. 
This prevalence of the enzymes of the youthful condition leads to the lique- 
faction of the diversely formed tissue groups. Such a displacement of the 
enzyme activity may be considered, in its effect, to be like a wave which 
continues to advance in the tree until it is stopped by some other constructive 
force. According to practical experience, such a halt is called by all those 
factors which condition a normal ripening of the wood and a precipitation, 
at the right time, of abundant quantities of reserve substances; porous soils, 
sunny open places, and a supply of calcium, avoidance of over-abundant 
nitrogen fertilization. 

In treating wounds v/hich are exuding gum, the use of vincijar made 
frum wine is warmly recommended on all sides. I have had no personal 
experience with it. 

Exudation of Gum in Other Plants. 

Exudation of Gum in the Acacia. 

Moller^ maintains that the formation of Acacia gum depends upon 
changes similar to those of the cherry gum. He says very generally that the 
gum of the Acacia is always produced by a transformation of the cell wall, 
advancing from the outside inward. The walls of the parenchyma cells and 
the sieve tubes are the first ones to fall victim to the dissolution. (The 
collapsed sieve tubes form Wigand's Horn prosenchyma.) Moller observed 
the gum also as a product of the bark and found that it differs according to 
the zone in which it is produced. Gum arable is produced by the dissolving 



1 Moller, tjbcr die Entstehung- des Acacien-Gummi. Sitzungsber. d. Akad. d. 
Wissenschaften. Wein. 1875, June issue. 



7o8 

of the inner bark while a less soluble form, similar to the cherry gum, occurs 
in the middle bark. This may well depend on the age of the affected tissue^. 

As one of the causes which give rise to the exudation of Senegal gum 
from Acacia Verek, Martins" mentions the action of dry desert winds which 
blow in the autumn and winter and cause the rupturing of the outer bark of 
the Acacia, which has become more furrowed because of the August and 
September winds. Other wounds, which result in the exudation of gum, 
are caused by a parasite which Martins calls Loranthus scnegalensis. 
Cryptogamic parasites are also able to cause the wounds to remain open 
permanently and they thus exercise a stimulus for gum formation. 
Coryneum gummiparum Oud., which Oudemans observed as bud form of 
Pleospora gummipara Oud., acts just as Coryneum Bcijerinckii does with 
the Amygdalaceae. 

Gummy Exudation of the Bitter Orange^. 

Italian plantations of bitter oranges (Citrus vulgaris), lemons (Citrus 
limonum) , and sweet orange trees (Citrus Aurantium) have suffered for 
many years from a disease which is constantly spreading, the "Mai della 
gomma" of the Italians, which causes such injuries that, according to 
Novellis'^, the Italian Department of Agriculture and Commerce has offered 
for years a premium of 25,000 lires for a proved means of curing it. 

The disease begins with the appearance of black specks in the bark of 
the trunk and branches, especially near the points of bifurcation. These 
spots increase rapidly in size, until, after a little time, they become black 
places in the bark and split open A yellowish white liquid exudes from the 
surface, which gradually becomes denser in consistency and stickier, and 
finally hardens into yellow beads, or glaze-like coatings. The wood under 
the opening in the bark is brown and in a process of gummosis. If the 
gum is washed by rain on to other parts of the tree, new centres of disease 
are said to be produced. We find similar conditions also in regard to the 
acacia gum and it is not at all impossible that such cases exist. Like the 
mosaic disease of the tobacco, this may be explained as follows : The 
enzymatic bodies causing the formation of gum give the impetus for similar 
changes in predisposed healthy specimens and spread further like a wave. 



1 For the different relations of cellulose and gums to each other in different 
mucilaginous exudations, compaie Tollens and Kirchner, Untersuchungen iiher den 
Pflanzenschleim; cit. Biedermann's Centralbl. 1S75, II, p. 28. In regard to the forma- 
tion of the sugar known as Galactose, frorn mucilaginous gums, soluble in water, 
when treated with dilute acid, see Gireaud, Etude comparative des gommes et des 
mucilages. Compt. rend. LXXX, p. 477. Peter Claessen, tjber Arabinose; cit. 
Jahresber. f. Agrikulturchemie, 1881, p. 88. 

2 Martins, Sur un mode particulier d' excretion de la g-omme arabique produite 
par r Acacia Verek du Senegal. Compt. rend. 1875, I, p. 607. Killani, tjtaer arabisches 
Gummi. Berl. chem. Ges. cit. Jahresber. f. Agrikulturchemie 1882, p. 88. 

3 Savastano, L. Note di patologia arborea. Napoli 1907. The work contains 
various contributions on g-ummosis which we unfortunately cannot make use of at 
present and can only mention as in the last proof sheets. 

4 Novellis, Ettore de, II male della g'omma deg-li agrumi; cit. Bot. Centralblatt 
1S80, p. 469. 



709 

The gummosis becomes fatal for the tree when the gum centres make 
up a greater part of the trunk circumference. According to Fliihler^ lemons 
suffer most and sour oranges least. Cuttings seem to retain the germs of 
the disease, and in the same way, grafted specimens seem to give a higher 
percentage of disease than seedlings which- have remained ungrafted. Rich 
fertilization, heavy watering, clayey soils, increase the evil, which is said to 
increase also if cover crops, like pumpkins, beans, tomatoes, etc., are grown, 
which require heavy fertilization. 

Judging by the material to which I have had access thus far, I consider 
the disease of Citrus fruits to be exactly the same phenomenon as the exu- 
dation of gum in the Amgydalaceae. I consider the excessive addition of 
fertilizers rich in nitrogen, to be one of the momentarily most frequent 
causes, which play a brief role also in Germany for the pitted fruits in 
nurseries. 

Among the Italian authors, Peglion- shares the theory explained here. 
He calls attention to the fact that the cultivation of cover plants needing 
rich fertilization is injurious. Stable manure is not very suitable for Citrus. 
The fruit, to be sure, becomes large but remains thick-skinned and sour. 

Blackleg of the Edible Che.stnut. 

According to Gibclli'' this disease is characterized by the appearance of 
wilted yellow leaves and small fruit, poor in sugar. In young trees the base 
of the trunk dries up, the bark turns brown, and its tissues contain concre- 
tions of tannin as large as the head of a pin. Analyses show all the charac- 
teristics of plants growing poorly, i. e. a large ash content in proportion to the 
dry substance. In the ash is found a scarcity of potassium and phosphoric 
acid and a considerable increase of ferric oxid. 

Because of the ball-lik^ concretions, giving the tannin reaction, the 
disease seems to me to be related to the disease "Mai Nero" of the grape- 
vine (see page 219). Comes^ describes this form as gummosis. According 
to Cugini^ this disease, because of which bud development is entirely 
retarded in the spring, or destroyed, is characterized by the appearance of 
black stripes and spots on the branches, petioles and ribs, tendrils, and stems 
of the clusters. The spots extend into the organs and, in fact, the trunk 
even to the heartwood. Besides this, the disease is characterized by the 
subsequent appearance of yellowish brown granules in the parenchymatous 



1 Fliihler. Die Krankheit der Agiumen in Sicilien. Bicdeimann's Centralblatt 
1874, p. 368. 

2 Peg-lion, V. La concimazione e le malattie nella coltura deg-li agrumi. BolL 
di EntomoL agrar., etc. 1901, in Bot. .Jahrestaer. 1901. T, p. 479. 

3 Gibelli, La Malattia del Castagno: cit. Bot. .Jahresber. 1879, II, p. 37.5. Gihelli 
ed G. Antonielli, Sopra una nuova malattia del Castag-ni, ibid. Cug'ini, Sopra una 
n'.alattia che devasta i castag^neti italiani, ibid. 

4 Conies, II Mai nero della vite. Portici 1882. Primi risultati deg^li esperimonti 
tatti per la cura della Gommosi o Mai nero della vite. Portici 1882. Sul preteso 
tannino scoperto nelle viti affette da Mai nero. Bot. .lahre-sber. 1882. 

■> Cug-ini, Ricerche sul Mai nero della Vite. Bot. Centralbl. 1881, Vol. VIII, p. 
147. Nuova indag-ini sul Mai nero della Vite. Bologna 1882. II Mai nero della Vite. 
Firenze 1883. 



;io 

elements of the trunk and branches. These granules often fill up the entire 
lumina of the cells and consist either of cellulose or of substances containing 
proteins. Cugini, who, morever, considers the phenomenon to be parasitic, 
also confirms the turning green of the blossoms and connects it with the 
disease. Differences of opinion prevail already among pathologists who 
have found parasites. Prillieux^ considers Rocsleria hypogaca as the cause, 
while Hartig" declares that this fungus is an accompanying phenomenon and 
that another, Dematophora necatrix is the real parasite. 

Later investigations, especially those made by Pirotta"', show that the 
above mentioned granules in the cells give the tannin reaction and arise 
directly from the starch grains. He found Rhizomorpha very frequently 
in the diseased roots, but not always ; nevertheless, he does not consider this 
fact important enough to place the disease among fungus diseases. Comes 
showed that the granules in question do not represent accumulations of 
tannin but consist of a different ground substance (gum) which is only 
saturated with tannin. 

GUMMOSIS OF THE FiG TrEE. 

The disease of the fig tree {Marciume del Fico" of the Italians), which 
has been well known since the time of Theophrates, has been thoroughly 
studied by Savastano*, who recognized it as gummosis. 

This disease, to which old plants are more exposed than young ones, is 
found most markedly in the months of July, August and September when 
the leaves become yellow and fall, as does the fruit also. Although numer- 
ous fungi and even insects are found on the wilted and dead leaves {Fumago 
salicina, Tul, Uredo Ficus, Cast, Phyllosticta Sycophila Thiim., Sporodes- 
mium, Coccus caricae Fab.), these parasites should not be considered causes 
of the disease. Usually there is no change in the trunk and branches, but a 
change does occur in the root, where the chief seat of the disease should be 
sought. In a highly advanced stage the roots seem blackish up to the 
crown. They sometimes split open, but oftener decay. 

It is found in plants, raised from sprouts, that the seat of the disease 
may lie in the roots of the mother plant, from whence the further distribu- 
tion takes place in all directions, but especially upward. The outermost layer 
is the most diseased ; only at times is the innermost layer destroyed to any 
great extent. When the destruction reaches the crown, the plant dies 
absolutely. 

When the disease appears, the cells and ducts are found filled with a 
substance which at first seems a lemon yellow and later a dark amber. At 
first the cell walls are covered with this and then the whole lumen becomes 



1 Prillieux, La pourridie des vignes de la Haute-Marne, produit par le Roesleria 
liypogaea. Paris 1882. 

2 Hartig', R. Rhizomorpha (Dematophora) necatrix. Der Wurzelpilz des 
Weinstocks. Unterauchungen aus dein foi-stbotanischen Institute zur Miinchen. 
1883, III, p. 95. cit. Bot. Centralbl. 1883, No. 46 (Vol. XVI), p. 208. 

3 Pirotta, Primi studi sul Mai nero o Mai dello Spaceo neolle viti 1882; cit. Bot. 
Jahresber. 18S2. 

4 Savastano, L.. II Marciume del Fico. Annuario della R. Scuola Sup. d'Ag-ri- 
cult. Portici, Vol. Ill, fasc. V, 1884, con 4 tav. cromot. (nach brieflicher Mitteilung). 



711 

filled with it. The starch disappears with the increase of these masses. 
Savastano observed, even in seedlings, a production of gum centres at the 
point where the young roots passed into the trunk and branches. I found 
similar conditions in the sweet cherry, which externally showed no trace 
of disease. 

Savastano found gummosis appearing also in the trunk and branches. 
He found a substance in its gum which seems to be similar to "Olivile" 
occurring in the gummosis of the olive. The gummosis of the trunk and 
branches starts in the gum glands found even in the roots of saplings. Only 
after the plants have become diseased with gummosis may the presence of 
Rhizomorpha be proved which other investigators have considered the 
causes of the disease. With the red discoloration of the walls, the paren- 
chyma cells of the roots undergo a process of humifaction in which the 
specific weight of the tissue becomes less and less because the organic 
substances disappear. 

A later work by Savastano^ gives the results of comparative experi- 
ments with specimens of Amygdalus Per sic a and Amygdalus communis, 
Primus Cerasiis, P. domestica, P. inititia, P. Mahaleh, and P. Armeniaco, 
as well as Citrus Aurantium, C. Limonum, C. vulgaris and C. nobilis, and 
also of Olca curopaea affected by gummosis. The results show that the 
gummosis of the plants named has much in common with that of Ficus 
Carica. In all, the formation of gum centres either takes place as a result 
of injury, or without any external cause. If the wound is overgrown 
quickly and completely, the gum formed dries up, as a rule, into brittle 
masses and remains uninjurious for the surrounding tissue. If, on the 
other hand, moisture is present on the wounded places, the gum remains 
soft and is easily carried over the surfaces surrounding the wounds, which 
also succumb to gummosis. 

The Exudation of Manna. 

In many plants, instead of gum, a hard, clear substance containing 
sugar comes from the bark of young trunks and branches, and is called 
Manna in trade. The liquefaction product contains Mannit which, when 
extracted with alcohol, can be obtained in fine white silky crystals, tasting 
slightly sweet, and may also be formed artificially from different sugars. 
Investigations of the Manna exudation were begun by Meyen-. According 
to him, the large amounts of Manna, which come from Italy, are obtained 
artificially from a kind of alder, the Manna Alder, by making incisions in 
the bark toward the end of July. From these incisions the Manna flows 
gradually as a thick, sweetish juice, hardening in the air. 

Resinosis. 

The exudation of resin (resinosis) is for conifers what exudation of 
gum is for the Amygdalaceae and the Manna exudation for the Oleaceae. 

1 Gummose caulinaire dans le.s Aurantiacees, Amygdalees, le Fig'uier, I'Olivier et 
noircissement du Noyer. Compt. I'end. T, Decelire, 1SS4. Reprint. 

2 Pflanzenpathulof^ie, p. 22S. 



712 

It sometimes occurs in the wood and sometimes attacks the parenchyma and 
bast cells of the bark. The first stages of the disease are found in the 
resinosis of the wood ; the mature condition consists in the formation of 
large quantities of uniform resin masses in cavities in the trunk and branches, 
which are usually called resin boils. It is well known that resin in the cell 
contents normally occurs in the form of drops or, as in the glue mats of 
many wood buds, in the intermediate lamellae of the cell wall, or finally, as 
in our pines and spruces, in definitely distributed, peculiar resin canals. The 
contents of many parenchyma cells near the resin canal show resin drops 
and starch grains, of which some not infrequently are provided with a resin 
coating. The immediate surroundings must necessarily f virnish the sub- 
stances which fill the large resin pockets. Whether this material is trans- 
ported in the form of resin, as N. J. C. Muller^ assumes, or in the form of 
some other compound and is only developed into resin where it is found as 
such, which theory Hanstein- is inclined to believe, is of little importance 
for our consideration. In this we have to maintain that the formation of 
considerable amounts of resin and gum is possible only through the transfor- 
mation of a plastic substance, flowing toward those places where tine 
liquefaction takes place, i. e. a positive loss of sap. To this it should be 
added for resinosis, as for gummosis, that the existing plant substance, in 
the form of wood and bark tissue and of starch grains, succumbs to lique- 
faction and that, in this way, considerable material is lost. According to 
investigations made by Karsten" and Wigand^, the wood at first seems 
resiniferous, i. e. saturated with resin and balsam. In most of the cells of 
this saturated tissue, the resin appears as a W"all coating, or as drops which 
have spread together tnitil the cells seem completely filled with the mass. 
The walls of the cells, originally thick, become thinner and thinner in the 
same degree as the amount of resin increases within the cell, until, finally, 
only a fine outline is left, which is gradually lost in the mass of resin. 

As in gum exudation, the medullary rays also seem to be longer 
resistent, since they are clearly seen to extend into the uniform resin mass 
of the dissolved wood cells surrounding them. For complete analogy in the 
two processes, there is lacking only the proof that, in the exudation of 
resin, an abnormal w^ood parenchyma is formed, which undergoes absolute 
resinosis. 

1 Muller (tJbei' die Verteilung der Harze usw. in Pringsheim's Jahrb. f. wiss. 
Bot. 1866 — 67, p. 3S7 ff) says the great amount of resin in the resin ducts cannot 
have reached that place except by penetrating' many cell walls. He finds the cell 
walls to be permeable for resin. Thin cross sections of pine wood left lying' for 
some time in water showed that all the i-esin in the cell walls has l)een I'eplaced 
by water. 

2 Hanstein (tjber die Organe der Harz- and Schleimabsonderung in dem Laub- 
knospen. Bot. Zeit., 1868, No. 33 ff.) speaks of the occurrence of resin hist in the 
grooves of secretion cells as small bands between the cuticle and the cellulose mem- 
brane. This is undoubtedly an important leason for assuming that "the lesin, which 
occurs in the foi-m of intermediate wall layers, first assumes its real character after 
it has passed through the cell wall in another form and been deposited as an inter- 
mediate layer." 

3 Karsten, H. tJber die Entstehung des Harzes, Wachses, Gummis und Schleims 
durch die assimilierende Tatigkeit der Zellmembranen. Bot. Zeit. 1857, p. 316. 

■1 Wigand, tJber die Desorganisation der Pflanzenzelle. Pringsheim'.s Jahrb. f. 
wiss. Bot. Vol. Ill, p. 165. ' 



713 



It has often been observed that the starch grains in resinosis succumb 
to hque faction just as in gummosis. Starch certainly furnishes a large part 
of the resin in the exudation. Wiesner^ states, for example, that resin bodies 
exist within the medullary ray cells of foliage trees and possess the structure 
of the starch grains. These rarely turn blue with the use of pure iodine but 
do so more often with iodine and sulfuric acid. With the use of ammoni- 
acal cuprous acid they give the cellulose reaction ; they react to ferric chlorid 
like tannin. W'iesner, therefore, concludes from his investigations that a 
large amount of the resin, occurring in nature, arises from starch grains 
themselves, or from starch grains which have been changed into tannin. He 
considers the tannin to be a connecting link between the cellulose and resin. 

We find in Nottberg's" very thorough work on resin pockets the proof 
that even in the exudation of resin an abnormal parenchyma wood is formed 
which succumbs to resinosis and liquefaction. Nottberg proves that, as a 
result of any injury, whatever, which extends to the cambium, this responds 
with the production of a "tracheidal 
parenchyma" which gradually passes 
over again into the normal tracheids. 
The tracheids of the sap wood which, 
as a result of the injury, come into 
contact with the outer world, stop up 
their lumina with a mass resembling 
wound gum, which is insoluble in 
alcohol but dissolves after treatment 
with Schultz's mixture. Usually res- 
inosis occurs at the same time in the 

wood bodv. The dififerent cells of 

" . J- 1 Fig-. 157. Cell.s of the tracheidal paren- 

the diseased parenchyma immediatelv chyma of Pinus Strobus with tiie resin- 
after their production begin to form '''^»''^"''' ^^y^'' '"g'.t^f,;!- )" '^'''^^' ^^"''" 
resin internally (resin cells). The 

membranes of the new cells of the tracheidal parenchyma liquefy very early. 
The unthickened elements, on the other hand, as long as they are retained, 
constantly show only the cellulose reaction. In the resin cells a definite layer 
may be recognized in which the resin is formed (resinogenous layer. Fig. 
157). Nottberg. from whose book the figure is taken, leaves undecided what 
this resinogenous layer is ; "a de\'elopmental product of the membrane, or of 
the cyptoplasm." 

The pathological formation of resin may be considered the most exten- 
sive process of liquefaction at present known in the vegetable kingdom. It 
. existed in the tertiary period as well as now. for Conwentz states in his 
monograph on the Baltic Amber trees {Pinus succinifera, Conw.), which 
has excellent illustrations, "there was scarcelv one healthv tree in the whole 




1 Sitziing-abericht d. Akad. D. Wissensch. zu Wien, Vol. 51. 

2 Nottberg, P. Experimentale Untersuchungen iiber die Entstehung von Harz- 
gallen und verwandter Gebilde bei unseren Abietineen. Zeitsch. f. Pflanzenkr. 1897, 
p. 133 ff. Hier auch weitere Literatur. 



7T4 

amber forest ; the pathological condition was the rule ; the normal one, the 
exception."^ We cannot better present the processes of resinosis than by 
showing copies of the amber sections" which Conwentz has reproduced (Figs. 
158-161). 

Just as at present, we find that the process of resinosis began as follows : 
— resinosis and liquefaction of the membranes, and finally of the whole cell 




Fier. 158. Process of turning- to resin, beginning- with the formation of a ly.sigenoiis 
resin canal in the wood. 205:1. (After Conwentz.) 




Fig. 159. Horizontal section. In the summer wood of an annual ring is a group of 

abnormal wood parenchyma cells (P). 56:1: The holes in the tissue were produced 

in sectioning. (After Conwentz.) 



together with its contents, set in in different groups between two medullary 
rays (Fig. 158). No anatomically different tissue is necessarily present 
here, but, in the majority of cases, such an one is present and in fact in the 
form of wood parenchyma which develops in tangential strips. Conwentz 

1 Conwentz, Monographic der ))a,Ui.schon P.ernsteinl)niuno, Danzig, 1.S90, p. 145. 



715 

describes these strips (Fig. 159) in the summer wood. Up to the present 
I have found them predominantly in the spring wood of our trees so that 
a new annual ring begins at once with the abnormal wood, or after only a 
few cell rows. I trace the production of these strips back to a transitory 
weakening of the bark tension (see Frost Phenomena). This abnormal 
wood parenchyma is shown in a complete stage of resinosis in Fig. 160. 
Masses of resin, or rather amber, already produced, can push out the bark 
away from the oldest part of the trUnk. Conwentz found such bark ele- 
ments in so good a state of preservation that he still could prove their 
nuclei. (Fig. 161.) 

Nottberg found, in the lic|uefaction of the solid tracheid parenchyma, 
that the tertiary membrane was retained longest ; this may be observed also 
in the spreading of the gum centres of the cherry. 




Pig 160. Horizontal section with abnormal parenchyma wood (P), which has begun 
to turn to sugar. The abnormal tissue lies in the summer wood. J is the edge of 
the annual ring. 210:1. (After Conwentz.) 



Nottberg distinguished good and evil wounds according to whether the 
wound heals at once or affects the surrounding tissue. It should still be 
noted that the trees, of which the wood normally has no resin canals at all 
(the white fir), are found to abound in resin canals after injury, especially 
in the edges of the callus. These investigations have been confirmed by 
V. Faber\ who also emphasizes the fact that the pathological resin canals 
are formed schizogenously. They anastomose in a tangential plane and 
form a connected network, while their open ends extend into the wound. 
Above these the resin canals are more abundant and longer than they are 
below them. 

In opposition to the statements that the cause of resinosis may always 
be sought in wounds, I must maintain, as in gummosis, that the processes 
of liquefaction can also arise autogenously, without wound stimulus. I 
have observed this in seedlings of pines from heavily manured nurseries, 



1 V. Paber, E. V. Experimentaluntersuchungen iiber die Pntstehung d. Harz- 
fliisses Itei Al)ietineen. Disseitation. I'ern 1901. 



7i6 



and found similar cases likewise in older plants of Psemlotsuga Douglasi, 
Abies Fraseri and Abies concolor, which showed swellings of the bark. 
These could be pro\ed to be a lysigenous widening of schizogenous resin 
canals. The trees stood on moist, marshy soil which had been heavily 
manured at intervals of two or three years. 

Recently, I have had opportunity to observe resinosis as a constitutional 
disease, i. e. as the manifestation, even in old trees, of a tendency throughout 
the whole plant body, to form resin excessively. I have distinguished this 
universal disease, as "chronic resinosis," from the "acute resinosis" pro- 
duced locally as a result of wound stimulus, and remaining localized, which 
is connected with the exudation of profuse amounts of resin^. Accordingly, 
in the future, a chronic and an acute gummosis would have to be distin- 
guished from one another and in 
the latter, the treatment of the 
^ wounds with vinegar, already 
recommended, might be success- 
ful. 

Formation of Resin in 
Dicotyledonous Plants. 

The production of resin and 
gum resin in dicotyledonous 
plants is found to be parallel to 
the processes described in the 
Ijreceding section. Svendsen" 
found that the gum resins of 
Sty rax. Liquidamber, Toluifera, 
etc.. are pathological products, 
produced as a result of injury. 
After every injury, which ex- 
tends as far as the cambium, 
wound wood is formed which is distinguished by its tracheidal, parenchy- 
matous character and which gradually passes over again into normal wood. 
The processes, therefore, are ever^-where the same, just as was described and 
illustrated under injuries due to the frost. The wound stimulus makes itself 
felt in the old wood by a stoppage of the ducts with tyloses, or the closing of 
them by Bassorin. The new wood, which is formed about the wound and at 
first is parenchymatous, has resin canals produced schizogenously ; and 
widening lysigenously. The resinosis thus attacks the wood parenchyma, 
with the exception of considerable parts of the medullary rays, and con- 
tinues later in the bark, where it becomes noticeable within the bark rays ; a 
fact which should be emphasized. In dicotyledons, as in conifers, the patho- 

1 Landwirtschaftliche Jahibiiclier 190S. 

-' Svendsen, Carl Johan. tJber den Harzfluss bei den Dicotylen, speziell bei 
Styrax, Canarium, Shorea, Toluifera und Liquidambar. Archif for Mathematik og 
Natur\ddenskab. Kristania 1905, Voi. XXVI, No. 13. 




Pig-. 161. Group of parenchyma cells from 
the outer bark which has been completely 
separated from the central wood cylinder by 
the turning to resin of an annular, abnormal 
zone of wood parenchyma. The nuclei may 
still be discerned in the bark cells. (After 
Conwentz.) 



7V 

logical formation of resin is perfectly independent of the presence of normal 
resin canals. The conditions seem to be more complicated in Peru and Tolu 
Balsam. 

Therefore, so far as we can examine the pathological formation of resin, 
it corresponds perfectly to gummosis and, therefore, the same theories, which 
we have expressed earlier, hold good for it. It is not the wound stimulus 
in itself which causes the liquefaction of the solid tissues, but enzymatic 
actions, which we cannot determine at present, manifested in the result that 
scattered tissue groups fail to develop normally and dissolve because of 
oxydation. These processes can be introduced by wounds but also arise 
from a changed nutrition. They are dependent upon a definite develop- 
mental phase, i. e. the time of the sprouting of the trees. Centres of lique- 
faction, already existing, may be increased by the transmission of their 
enzymes to normal, permanent tissue. 

Supplementarily, we will cite a number of phenomena, some of which 
belong directly to degeneration due to gummosis, and others belong here 
because we conceive them to be the results of enzymatic disturbances of 
equilibrium. 

Analogous to the exudation of gum is the exudation of transparent 
gummy masses in Elcagnus canadensis, occurring especially about the edges 
of wounds, Frank has descrilted it more exactly. I fotmd the formation 
of gum in palms, cucumbers, cacti, and hyacinth bulbs\ 

I assume an enzymatic disturbance in the heart rot and the black ring 
condition of the horse radish'-, the glassiness of cacti, orchids, carnations, 
etc. Conditions of weakness are thus created which render the plant sus- 
ceptible to parasitic attacks. Wood has referred to this point with especial 
distinctness : "I called special attention to the fact that plants rich in 
oxidizing enzymes were more sensitive to unfavorable conditions of tem- 
perature, moisture and especially to insect enemies tlian plants poor in these 
enzmyes."* 



1 According- to Comes, the "Bni.sca of the Olive" is a decided gummosis. 

2 s. Zeitschr. f. Pflkr. 1899, p. 132. 
* Loc. cit., p. 22. 



SFXTION IV. 



EFFECTS OF INJURIOUS GASES AND LIQUIDS. 



CHAPTER XVI. 



THE GASES IN SMOKE. 



SuLFUROus Acids. 

The injuries to vegetation due to the gases in smoke have become so 
numerous and varied, with the constantly increasing spread of textile indus- 
tries, that the study of them begins to form a separate branch of pathology, 
in which chemistry and botany are equally concerned. It is thus evident 
that this branch of science demands special attention. The subject has 
been most extensively treated in Haselhoiif and Lindau's book' and later in 
that of Wieler'-. Because of the abundance of material on injuries from 
smoke we can here merely refer to these works and treat more thoroughly 
only the points less fully taken up in them. 

For a long time, scientists were in doubt as to which element in the 
smoke was the injurious one, until the investigations of Morren^, .Stock- 
hardf* and especially v. Schroder^ proved it to be the sulfurous acid. The 
metallic poisons, like arsenic, zinc and lead, to which especial attention was 
formerly paid in studying the injuries due to the smoke of smelting houses, 
have been proved experimentally to be less injurious to our cultivated plants, 
while a very small addition of sulfurous acid to the air is able to bring about 
the death of the plants under experimentation. How small this addition 
need be is shown by Morren's'' observations. He could perceive the charac- 
teristic indications of destruction in the leaves even when the air contained 



1 Haselhoff, E., und Lindau, G., Die Beschadlgung der Vegetation durch Ranch. 
Berlin 1903, Borntrager, 412 pages, with 217 illustrations. 

2 Wieler, A. Untersuchungen liber die Einwirkung schwefliger Saure auf die 
Pflanzen. Berlin 1905, Gbr. Borntrager. 

3 R6cherches experimentales pour determiner I'influence de-certains gaz indus- 
triels, specialement du gaz acide sulfureux, sur la vegetation. Extracted from the 
Report ol: the International Horticultural Exhition, etc. London 1866. 

* Untersuchungen iiber die schadliche Einwirkung des Hiitten- u. Steinkohlen- 
rauches auf das Wachstum der Pflanzen. Tharandter forstl. Jahrb., Vol. 21, Part 3. 

•'■' Die Einwirkung der schwefligen Saure auf don Pflanzen, in Landw. Ver- 
suchsstationen 1872. 

c Ijoc. cit., page 224. 



719 

only 1-50,000 of its volume in sulfurous acid. Schroder states^ that one 
one-milHonth will prove injurious if allowed to act for some time. Such 
slight amounts are certainly present in many kinds of smoke, formed by the 
oxidation of hard coal, which contains sulfur. Moreover, since sulfur in 
the form of iron sulfid is an abundant element in hard coal, it may be 
assumed that, as Morren says, we establish a poison centre for plants with 
every chimney we erect. 

Yet, at any rate, we should not carry this anxiety too far. The experi- 
ments, proving the injuriousness of such small amounts of gas, were made 
in a space enclosed by a bell jar and the gas usually acted for several hours. 

This corresponds in ever}^day hfe only to the constitution of the air 
in the immediate proximity of an industrial establishment, such as smelt- 
ing house, coke oven, etc., in a narrow valley where the smoke lies day 
and night in great masses above the vegetation. In the majority of cases 
the motion of the air, and especially wind, together with the character- 
istic oxidation of sulfurous acid into sulfuric acid when in contact with 
moisture, serve as a protection against the most extreme action of the 
poison, and against immediate death. In any case, however, it would be 
well, in regions where hard coal or peat- is burned, to choose for industries 
producing a great deal of smoke, such positions as are removed as far as 
possible from large plantations, especially from tracts of trees. 

The gaseous products, from burning hard coal free from sulfur are not 
injurious to vegetation^. If the coal, however, contains som^e sulfur and gives 
it off into the" air as sulfurous acid, it will be taken up by the leaf-organs 
of the conifers and deciduous trees. According to v. Schroder the greater 
part is retained in these organs and only a small amount is carried into the 
wood of the plant. The experiments made by Freitag* directly in this con- 
nection indicate that we shall have to consider the leaves as the main organs 
for taking up the poison. Yet all leaves do not take up equal amounts of 
the poison offered them; in this, conifers differ markedly from deciduous 
trees. Under similar external conditions, with equally large leaf surfaces, 
the former take up less sulfurous acid than do the latter. Yet it can not 
be said that a plant suffers more when it has taken up a greater amount of 
gas. The power of resistance depends rather upon the special organization 
of the plant. In this connection, the supposition is pertinent that the 
anatomy, especially the number of stomata, may be determinative for the 
sensitiveness of a plant. This supposition, however, which has been repeat- 
edly expressed by Morren, has proved to be erroneous, since Schroder has 



1 Schroder, .J. v., und Reiiss, C. Die Be.schadigung' der Veg-etation durch Raucli 
usw. Berlin 1S83, P. Parey. 

2 According to Stockhardt the smoke from lignite and peat is also injurious, for 
this fuel contains sulfate of silica. The smoke of lime kilns is less injuiious because 
the lime retains the sulfurous acid form, jYist as in brick ovens the magnesia content 
frequently present in the clay acts favorably because of the retention of the sulfurous 
acid. Chemischer Ackersmann 1872, Part II, p. Ill ff. 

3 Proved for plum and pear trees. 

4 Mitteilung der landwirtsch. Akad. PoppeLsdorf. Vol. II, 1869, p. 34 cit. bei 
Schroder loc. cit., p. 321. 



720 

found that the sulfurous acid is taken up not only by the stomata but 
uniformly by the entire upper surface of the leaf. He found that just as 
much gas was taken up by the upper side, free from stomata, as by the 
underside which abounds in these respiratory organs only the action of the 
gas which had penetrated the underside was much more rapid and energetic. 
This is explained by the fact that sulfurous acid is greedily absorbed by 
water and oxidizes easily in contact with it. Now, since the loss of water 
from the leaf into the air takes place especially through the porous under- 
side which abounds in stomata, the action of the gas manifests itself so much 
the more here. If the water in the micellar interstices of the cell-walls is 
combined with the acid in greater amounts than can be supplied to the 
walls, they become deficient in water and finally dry up, thereby losing their 
capacity to conduct water. 

Thus only those cell bodies will remain well supplied with water and 
will retain their normal color, which lie directly against the rapidly conduct- 
ing tissue of the vascular bundles while the dry part, lying between the 
vascular bundles (the leaf veins) takes on a faded, brownish color. This 
phenomenon of bright green venation in a faded leaf mass has been taken 
as- a characteristic point for recognizing leaf poisoning from sulfurous acid. 
Hartig^ maintained that the red eoloration of the guard cells of the stomata 
in conifers is a positive characteristic of injury due to acid. This statement, 
however, was immediately refuted by other observers. Wieler" and 
Sorauer^ have proved that slow death, under the influence of light and with 
the action of very different factors causes a red coloration. Directly in 
connection with this characteristic, apparent to the naked eye, is the 
decreased water evaporation from poisoned leaves, as found by v. .Schroder 
in weighing experiments. The amount of the transpiration may be used, 
however, as the expression of the amount of production and thus it may be 
concluded here that the leaf-assimilation is less. The general effect of the 
poisoning on the plant body will, therefore, resemble permature defoliation 
and, in fact, the action sets in the more quickly the greater the amount of 
sulfurous acid present, the drier the air, the higher the temperature and the 
stronger the illumination, which are the factors inciting the leaf to more 
intensive activity. Becausd of this fact, which has been determined experi- 
mentally, the supposition that tjie smoke from smelting works and from 
hard coal will act less vigorously at night than during the day is pertinent, 
and we will find later that it is confirmed. 

Caution is necessary, however, when forming one's judgment from the 
characteristic of green venation and dried middle fields. Almost all injurious 
atmospheric effects express themselves in such a way that the parts of a leaf 
lying furthest from the water-conducting ribs, namely, the fields between 



1 Hartig, Rob. tjber die Einwirkung- des Hiitten- und Steinkohlenrauches auf 
die Gesundheit der Nadelholzbaume. Munchen 1S96, Rieg-er'sche Buchhandl. 

2 Wieler, tJber unsichtbare Rauchschaden bei Nadelbaumon. Zeitschrift liir 
Forst. 11 Jagdwesen 1897, Sept. 

s Rorauer, P. tJber die Rotfarbiing von SpaUriftnungcn bei I'icca. Notizbl. 
d. Bot. Gart. Berlin 1896, No. 16. 



721 

these ribs (intercostal fields), suiter earliest and most extensively from 
frost, sunburn, etc. With the action of the acids in smoke, however, the 
boundaries between the dead and healthy tissues are as sharp as usual, while 
with the action of atmospheric factors they are less distinct because of the 
many transitional stages. 

The appearance of the injury in decidedly smoky districts also differs 
because, besides sulfurous «cid others, such as sulfuric acid, hydrochloric 
acid, hydrofluoric acid, etc., become efl^ective. The action of these acids 
strongly soluble in w^ater (hygrophilous) is restricted, however, to the 
immediate surroundings of the centre of production, where they act at any 
rate much more intensively and kill the tissue rapidly, while sulfurous acid, 
distributed in a gaseous form over wide districts, is usually breathed in by 
the plant slowly but j)ermanently. The former effect, appearing rapidly and 
eating into the tissue, is distinguished as "acute" from the phenomenon of a 
slow poisoning which is termed "chronic injury from smoke." Of course, the 
latter must ha\e made itself felt inside the plant before the external char- 
acteristics appeared. The chlorophyll apparatus is changed (as has been 
proved by W'islicenus^ with the spectroscope and by Sorauer- with the 
microscope) even if the plants still appear perfectly normal. In this case an- 
"invisible injury from smoke" is spoken of. Naturally such disturbances 
can be averted very easily and the plant, as has been found, is in a position 
to cure itself after the cessation of a weaker action of smoke. 

Such cases will also occur in forestry if changes in local conditions take 
place which divert a stream of smoke or dilute it to the point of uninjurious- 
ness. Wislicenus^, to whom we owe recent especially thorough, conscien- 
tious investigations, states that the point of uninjuriousness is 0.0005 P^^" 
cent, of the volume. 

He emphasizes the fact that, aside from the extreme individual differ- 
ence in sensitiveness, the stage of development of the plant is of decisive 
significance. The time when the new leaves and needles unfold is the most 
critical ; the plants suffer most then, because the cuticular covering of the 
epidermis is still insufficiently developed. The above-mentioned influence 
of light, which promotes injury and was observed by v. Schroder and Hartig, 
has been tested experimentally by Wislicenus*, who found that visible 
injuries did not appear in young spruces in the dark and in winter, although 
an increase of the sulfur content could be proved. Ramann and Sorauer"' 
have also observed that the amount of demonstrable sulfur in an organ is 
not determinative for the degree of injury and Count zu Leiningen*' calls 



1 Wislicenus, Resistenz der Fichte gegen saure Rauchgase bei ruhender und 
tatig-er Assimilation. Tliarandter Forstl. Jahrbiicher 1898, Sept. 

2 Sorauer, P.. u Ramann. E. Sogenannte unsichthare Rauchbeschadigiingen 
Bot. Centralbl. 1899, Vol. I.XXX. See also Brizi in Zeitsch. f. Pflanzenkrankh. 1904, 
p. J 60. 

3 Wislicenus, H. Massnahmen gegen die Ausbreitung von Hiittenrauchschadcn 
im Walde. Referat 5 der Sekton VIII d. Inteimat. landw. Kongresses in Wein 1907. 

4 Tharandter Forstl. Jahrbiicher 1S9S, p. 152. 
•'■' Loc. cit. 

•5 Graf zu Leiningen, W., Licht und Schattenblatter dei' Buche. Xatiuwiss. Z. f. 
Landw. u Forstw. III. Jahrg-. Part 5. 



722 

allcnlion to a factor which is of decisive importance in making tests as to the 
estimate of injuries due to acid viz., to the very different amounts of sulfur 
and chlorin in shade leaves as contrasted with sun leaves. He found in the 
be^ch in one square meter of leaf substances: — 

in sun leaves in shade leaves 

SO3 0.2730 g. 0.3004 g. 

CI 0.0190 g. * 0.0347 g. 

Therefore, the less abundant the production of organic substances is 
the relatively higher becomes the content of sulfuric acid and chlorin. The 
statements of Wislicenus express the same : "A poorer soil quality, that is, 
soil constitution of less value physically and chemically, soils specifically 
unsuitable for the plant genus or primarily insufficient, excessive, or abnor- 
mally varying water content of the soil create a predisposition to disease 
from smoke ; among them the chief factor is the lack of water." 

The fact that the conditions in a forest become different because of the 
falling of the needles and the dying of the branches, indeed, that the appear- 
ance of deciduous trees is changed, that the trunks become almost entirely 
free from lichens^ and that the bark of the trunks of beeches takes on a 
peculiar grey tone, may be mentioned only in passing. The statements of 
V. Schroder and Reuss point directly to the change in soil constitution. 
They still say that an accumulation of undecayed needles is formed under 
spruces chronically injured by smoke and a complete absence of all living 
vegetation is noticeable as far as the dropping from the tree extends. This 
indicates a "poisoning of the soil." This is proved by Reuss' experiments, 
in which he carried soil from a smoke filled region into a zone free from 
smoke and set out plants in it. After three years, the loss in i to 2-year-old 
seedlings of the ash amounted to 100 per cent., of the maple 92 per cent., 
of the beech 72 per cent., of the spruce and pine 8 per cent., and of the 
oak, none. 

Wieler- has now taken in hand especially the question of soil poisoning 
and has proved that under certain circumstances in smoky regions with a 
continued out-pouring of smoke, sulfurous acid could be proved to a depth 
of 30 cm. and had, therefore, not been changed into sulfuric acid. The 
latter will also remain uninjurious only so long as it can combine with 
bases. If these bases are used up in neutralization and are washed away by 
rain the humic acid present finds no possibility of combination. In fact, all 
the soil tests made by Wieler, from regions injured by smoke, showed great 
amounts of humic acid. Calcium, which could have combined with the 
humic acid produced is, therefore, not present in these soils. The other 
bases, however, with which the humic acid forms soluble compounds (mag- 
nesium and iron) must have disappeared from the soil. Thereby, naturally, 
the absorptive power of the soil becomes poorer for other mineral nutritive 
substances. This refers also to the alkali forming soluble compounds of 

1 Lindau, loc. cit., p. 120. 

- Wieler, Neuere Untersuchungen, etc., p. 314. 



723 

humic acid which Hkewise pass into the subsoil. The lack of calcium makes 
more difficult the decomposition of the humus substances and the nitrogen 
enclosed in them remains inaccessible to the plants. At times the bacterial 
flora is scanty in acid soils. The free sulfurous and sulfuric acids may act 
injuriously also on animal organisms such as earth worms. Soils in smoky 
localities will become impoverished or poisoned by all these factors. 

\\^ieler ascribes the death of plants and especially chronic injuries to 
the scantier absorption capacity of soil, which has been poisoned and weak- 
ened by sulfuric acid or also by hydrochloric acid, but certainly goes too 
far into this, since all experiments show that the direct contact with the 
smoke forms the chief cause of death of the aerial organs: also comparative 
chemical analyses of the foliage and of the soil from which it is produced, 
do not always indicate an impoverishment of the supply of bases, but at 
times, in fact, a strong increase of calcium and magnesium^ Yet, neverthe- 
less, this aspect of the effect of acid smoke remains of the greatest impor- 
tance and the attention of practical workers should be directed to period- 
ically repeated application of calcium to the soil. 

We must refer to special works for the influence of currents of air and 
their constitution, especially their water content, as well as for proving acids 
in the air and the regulations for overcoming injuries due to smoke. We 
would like to mention only that Ost- has given a simple method for deter- 
mining the amount of sulfuric acid in the air. He saturated small pieces 
of cloth with corrosive barite and dried them. He then hung them in 
exposed positions in the places where the experiments were being made and 
after a certain time investigated their sulfuric acid content. By this method 
even pure mountain air showed a certain amount of sulfuric acid as its 
normal mixture, which must increase significantly in the neighborhood of 
villages. We have found recently in a lecture by the chief forestry com- 
missioner, Reuss", a summary of the requirements of foresters for the pro- 
tection of the forest against smoke. He indicates the necessity of forming 
indemnification societies in regions where many factories are placed close 
together. 

The fact should not be left unconsidered that when damages are 
demanded the objection is raised not infrequently by the injuring smelters 
and factories that eating by insects is the chief cause. In this connection, 
Gerlach* calls attention to the fact that spruce plantations, diseased by 
smoke, are preferred by the resin weevil. Not only Pissodes Hcrciniac and 
P. scabricollis, but also other insects, like Grapholithia pactolana and G. 
Chermes increase to a devastating degree in forests injured by smoke. 



1 Die landwirtsc.haftliche Versuchsstation in Miinster i. W. Denkschrift von J. 
Kcinig-. Mtinster 1S96, p. 191 ff. 

2 Ost, H. Die Verbreitung- der Schwefelsaure in der Atmosphare. Die chem. 
Industrie 1900; cit. Zeitschr. f. Pflanzenkrankh. 1901, p. 24.S. 

3 Reuss, Karl. Massnahmen gegen die Ausbreitung- von Hiittenrauchschaden 
im Walde. Internal. Landw. Kongress zu Wein 1907, Section 8, Ref. 5. 

* Gerlach, Beobachtungen und Erfahrungen liber cliarakteristische Beweis- 
mittel uzw. Merkmale von Rauchscliaden. Osterr. Forst- u. Jagdzeitung-; cit. Bot, 
Centralbl. 1907, No. 40, p. 360. 



724 

Hydrochloric Acid and Chlorin. 

Besides sulfur, hard coal also contains chlorin in the form of sodium 
chloride The chlorin content varies between o.i to 2.0 per cent. Leadbetter 
found in hard coal 0.009 to 0.028 per cent, of chlorin-. This, however, could 
not be proved in the ash and must, therefore, have been forced out with the 
volatile substances. Meinecke has also directly proved the presence of 
chlorin in the gases of blast furnaces^ and Smith* calls attention to the 
chlorin content of rain water in regions where hard coal is burned in consid- 
erable amounts. According to these statements, therefore, we must not 
consider any single injurious factor in the smoke of hard coal but different 
combinations of several factors. The difference will depend, on the one 
hand, on the composition of the coal and, on the other hand, on its use 
industrially. 

Because of the rapid formation of hydrochloric acid from chlorin in the 
presence of moisture and light both these factors must be treated together. 
In connection with sulfuric acid, mention has already been made of the 
impoverishment taking place possibly from the continued action of hydro- 
chloric acid in the soil. The action of direct solutions of chlorin alkalies 
will be mentioned in connection with cooking salt. The action on the plant 
varies according to its species, the season of the year, or the place and 
individual development. In general, this results in a bleaching and drying 
of the leaf edges, or also of the intercostal fields in which chlorin vapor acts 
more quickly than does hydrochloric gas. In contrast to sulfurous acid, 
however, dry leaf edges preponderate here. It was observed in the experi- 
ments made by Ramann and Sorauer (see Sulfurous Acid) that spruces 
sprinkled with water absorbed, on an average, less chlorin than plants not 
moistened. 

The studies on the changes in anatomy have up to the present led to 
contradictory results. Thus Lindau^ observed in Abies an alteration only 
at and near the stomata, while Kinderman^ confirms the investigations of 
Leitgeb and Molisch, that the guard cells possess the greatest power of 
resistance to injurious factors (among others, acids), which probably arises 
from a special constitution of the cytoplasm. 

Because of the uncertainty of results up to the present time, I will 
repeat here briefly the results of my own studies on grain and spruce'. At 
first the heavy general falling off in reproduction which the plants undergo, 
because of the hydrochloric vapors, and which manifests itself in the quan- 
titative proportions and the formation of the grain, has been found to be very 



1 Hasenclever, tjber die Beschadigung- der Vegetation durch saure Gase. 1S79, 
p. 9. Berlin, Springer. 

■■i Chemical News 1860, No. 46. 

3 Dingler's Journal 1875, p. 217. 

4 Bericht iiber die Entwicklung der chem. Industrie von A. W. Hofman, 1875. 

5 Log. oil., p. 244. 

6 Kindermann, V. Uber die auffallende Widerstandskraft der Schlies-szellcn 
gegen schadliche Einflusse; cit. Just. Bot. Jahresber. 1902, II, p. 653. 

7 Sorauer, P. Beitrag zur anatomischen Analyse ravichbeschadigter Pflanzen. 
Landwirtsch. Jahrbiicher 1904, p. 587. 



725 

p)ronounced ; this conHrms the investigations of Wieler and Hartleb^. Such 
an effect can occur without an indication of a disturbance in growth by any 
striking external characteristics. As a rule, however, this disturbance in 
growth is accompanied by a discoloration of the chloroplasts and their subse- 
quent balling. There then follows a contraction of the primordial sack and 
a shrivelling of the chlorophyll grains. The leaf thus injured may still at 
times live out its life normally, depending upon the intensity and length of 
action of the chlorin. Usually, however, it dies prematurely, in part or 
entirely. . In the latter case, principally the leaf parts die, for which, because 
of their position and the lesser development of mesophyll and vascular 
bundles, the supply of water is acquired less easily and is smaller ; these are 
the tips and edges of the leaf. Therefore, we find dry, discolored leaf tips 
in grain and narrow dry outlines on both sides of the lower part of the leaf 
surface which still remains green. As a result of rapid death, a compara- 
tively important condition is found in the cell content of the dead parts. 
The drying with the retention of air in the tissue is connected with a shriv- 
elling of the cells ; yet in such a way that the walls of each cell do not touch 
one another. The natural process of drying, on the other hand, which 
occurs only after complete impoverishment of the cell content, is character- 
ized by the entire collapse of the mesophyll cells, in which the upper wall 
falls against the lower wall and the whole flesh of the leaf, formerly green, 
represents a pale straw colored strip of dense tissue with curving walls lying 
upon one another in layers. The collapse of the cells in different varieties 
of grain, with the exception of barley, extends almost entirely in the meso- 
phyll during the natural process of drying, while the epidermal cells retain 
approximately their normal height. In barley (characterized by practical 
workers as "soft"), the epidermal cells also collapse in a natural death. But 
in this, some of the widest cells of the upper surface form an outward fold. 
In a cross-section through the dead leaf this appears as a conical protuber- 
ance resembling a hair and gives the whole cross-section the appearance of a 
thin, knotty spiny cord. 

Because of the importance of distinguishing a leaf which has died a 
natural death from one destroyed prematurely by acid gases, we will illus- 
trate a leaf injured by acids and one which has died normally. Fig 162 / 
is the cross-section through the edge of an oat leaf dried by hydrochloric 
acid, or chlorin vapor. It is seen that the tissue has shrivelled greatly, 
especially between the ribs (the intercostal fields) without the mesophyll 
having had time to become empty. The cell contents appear a dirty green 
to a brownish green color and variously contracted. The walls of the bast 
layers at the angles of the leaf (B) and below the vascular bundles (b) like 
the epidermis are colored a reddish yellow to a brownish yellow and the 
epidermal cells in places (s) are so dried that the upper wall touches the 
lower wall. Fig. 162, ^ is a magnified cell group from 162, /, showing the 
still abunda nt cell content. 

1 Wieler, A., and Hartleb, R. tjber Einwirkung der Salzsaure auf die Assimi- 
lation der Pflanzen. Ber. d. Deutsch. Bot. Ges. 1900, p. 348. 




Fie 162. Difference between an oat leaf dried by the fumes of chlorin or hydro- 
^' chloric acid and one which has died a natural death. 



• y27 

Fig, 162, J illustrates the cross-section through a normally dried oat 
leaf from a locality free from smoke. In the cross-section the leaf appears 
as thin as a cord because the mesophyll (V) is approximately empty and the 
cell walls have collapsed. The leaf does not shrivel in the same way around 
the larger vascular bundles because the strong layers of bast serve as stiffen- 
ing; they look like knots in the cord-like form. In spite of the great drying 




Fi£ 



163. Leaves of a red beech, affected by sulfiuous acid. 

and Reuss.) 



(Alter V. Schroder 



of the leaf, the epidermis retains its natural height and at most turns a pale 
quince yellozv like the bast cords, and is thus distinguished from that injured 
by acids. Fig. 162, ^ is a magnified group from Fig. 162, j. E indicates 
the epidermis ; below this, the collapsed mesophyll cells in which the scanty 
cytoplasmatous remnants of the cell content have been made recognizable 
by soaking the section in water. Also in the oat leaf which has matured 
slowly in continued wet weather the ])art injured Ijy acid differs in color 



728 

from the normal since it has assumed a lemon yellow color in the walls of 
the bast layers and epidermal cells. The intensity of the discoloration is 
connected with the quality of tannin. In observing differences in color one 
must work quickly, since the coloring matter is soluble in water. 

All that has been said here of grain varieties may not be applied iwithout 
limitation to other plants. As a general occurrence may be considered only 
the fact that in all kinds of sudden death, the cell contents are abundantly 




Fig'. 164. Birch leaves injured ))y suUurons ncid. (After v. Schriider and Rens.s.) 




Pig'. 165. Rose leaf and 

injured by hydrochloric acid or chlorin lumes. 



Fig-. 166. Beech leaves 
(After V. Schroder and Reuss.) 



retained, while they are for the most part used up in respiration when the 
leaf has lived out its life naturally. 

In order to emphasize the habitual differences in the manner of attack 
of the vapors of sulfurous and hydrochloric acids we will give here illustra- 
tions of injured leaves copied from the repeatedly cited works of v. Schroder 
and Reuss. 

In Fig. 163 we see a leaf of a red beech taken from the vicinity of a 
silver smelter, which had been injured by SO.. Fig. 164 shows a birch leaf 



729 



from the neighborhood of a copper mill likewise injured by SOo. The com- 
mon characteristic consists of more or less sharply defined brown specks in 
the intercostal fields. The spots are usually surrounded by a brown zone 
which may vaiy in tone. In many trees (for example, the red beech) a 
transparent yellowish green band of diseased but not dead tissue is found 
around this peripheral zone. 

Figures 165, 166 and 167 illustrate leaves from a rose plant, a beech 
and a birch, which have been artificially injured by hydrochloric acid. They 
have the dry periphery, which may usually be observed after the action of 
pure chlorin vapor. Nevertheless, it should be emphasized that in testing 
smoke effect no definite conclusion may be drawn from such structural 
pictures showing the habit of growth, because, on the one hand, the forms 
of injury var}^ according to 
the individual h^ibitat and de- 
velopment of the tree and, on 
the other, different factors 
may produce similar injuries. 

Hydrofluoric Acid. 

More often than was for- 
merly supposed, hydrofluoric 
acid produced by the opera- 
tion of superphosphate, glass 
and chemical factories has 
proved injurious to vegeta- 
tion. The fact, at first so 
puzzling, that smoke from 
kilns and terra cotta factories 
is very injurious in many 
cases and in others non-inju- 
rious has been explained by 
this action of the acid. The 
difference in effect depends 
upon the presence and amount of fluorin compounds to be found in the clay 
and raw phosphates. According to Ost, action manifests itself in small, 
brown, corroded spots which in many plants are surrounded by a yellowish 
zone. Smoke experiments carried on by other investigators produced in oak 
leaves nan^ow, yellowish brown, sharply defined peripheral discolorations. 
The Norway maple showed similar tracery along the edges of the leaves and 
the leaf surface and later also turned brown. Lindau^ describes the ana- 
tomical condition in the oak. He found both of the e[)idermal layers to be 
intact and the contents of the mesophyll cells slightly browned. The indi- 
vidual chloroplasts were still recognizable, "but the rest of the cell contents 
had an oily appearance." 




Fis:. Ifi7. Birch leaves injured by hydrochloric 

acid or chlorin fumes. (After v. Schrclder and 

Reuss.) 



1 Loc. cit., p. 250. 



730 

In regard to the forest trees, which come most under consideration, we 
find it stated that the spruce, even one day after artificial smoking, shows 
some shoots with a whitish gray discoloration ; in fact, they had wilted. 
After a second smoking the little trees were set out of doors, where the color 
tone, which originally had been a whitish, yellowish gray, passed through all 
the gradations from yellow and yellowish red to the "characteristic red of 
injury from acids." 

Pines, larches, and acacias, like the spruce, were found to be discolored 
in the vicinity of a phosphate factory where hydrofluoric vapors were devel- 
oped in the removal of phosphorite containing the calcium-fluorin by the 
use of sulfuric acid\ Mayrhofer- was able to prove a strikingly high 
content of fluorin in the needles and leaves at a distance of 500 to 600 m. 
from the factory. The effect of such an exhalation may be absolutely 
destructive to grain. Thus Rhode' observed that in some plots rye devel- 
oped no kernels at all, or only deformed ones. 

My own investigations were made only on preserved material of dead 
spruce needles which I had received from Professor Ramann, but, what is 
most important, the condition found in them agreed with the effects obtained 
with sulfurous acid. Only, in the needles affected by the hydrofluoric acid, I 
found, however, a wrinkling of the tissues as a result of the shrivelling of 
the cell walls. It must be concluded from this that the drying of the needles, 
which appears so quickly with the use of sulfurous acid, takes place only 
after the direct action of the acid has already produced a change in the form 
of the tissues. The contents, however, had not dried against the walls as in 
the action of sulfurous acid, and, on this account, could not have contributed 
to the stiffening of the walls themselves. 

Nitric Acid. 

We find only one note by Konig* on the influences of nitric acid (or 
nitrogen tetroxid). With 5 grains nitric acid (reckoned on nitrogen 
tetroxid) to 100,000 1, of air or 0.05 g. of nitrogen tetroxid in one cubic metre 
of air, he found characteristics occurring in trees which resembled those 
appearing after the action of sulfurous acid and hydrochloric acid. The air 
generally contains only 0.00003 &• of nitric acid in one cubic metre. 

Ammonia. 

Ammonia and ammonium carbonate in quantities far beyond that of the 
usual content of the air, which at most may be assumed to be 0.056 mg. per 
cubic metre, were found to favor growth. In general manufacturing pro- 
cesses, however (ammonium sodium processes, etc.), such large amounts 



1 Allgem. Forst. u Jagdzeltimg- 1891, p. 220. 

2 Mayrhofer, J. tjber Pflanzenbeschadigung, veranlasst durch den Betrieb 
einer Superphosphatfabrik. Freie Vereinigung- d. Bayr. Vertreter fiir angewandte 
Chemie. Vol. X, p. 127. 

y Rhode, A. Schadigung von Roggenfeldern diirch die einer Superphos- 
phatfabrik entstromenden Gase. Zeitschr. f. Pflanzenkrankh. 1895, p. 135. 
4 Konig, Denkschrilt 1896, p. 202. 



73 T 

become free that they produce injuries, although the plants in general are 
found to be very resistent. The sensitiveness of different species varies 
greatly, but the kind of injury shows a great uniformity; namely, a black 
coloration occurring in spots or surfaces. 

Experiments made by Borner, Haselhofif and Konig^ exhibited in the 
oak the appearance of dark spots or a complete blackening of the leaves. In 
the cherry at first a brown color w^as seen and later black. After a short 
exposure to the action of ammonia the leaves and blades of barley were 
bleached white on the side turned toward the sun. Rye and wheat showed 
rusty spots and edges. 

In addition to the cases already known in literature, I will add here a 
few of my own observations. I found the leaf tips of barley turning white. 
The intercostal fields of young chestnut leaves were dark at first, but became 
black the next day and later dried up. The foliage of some of the red blos- 
soming varieties of Azalea indica behaved similarly, while in a variety stand- 
ing nearby but bearing white blossoms only a browning of the leaf tips and 
edges appeared. Along the edges of the outermost tips of blossoms of the 
red variety, white, nearly round, or wedge-shaped spots resembling a natural 
\'ariegation were found, while blossoms of the white variety within the same 
length of time remain unchanged with the exception of scattered small, 
brown spots. No after effects could be perceived after the plants had been 
removed from the ammonia atmosphere ; but there was some reaction in the 
inflorescence of a cineraria. The red, outer blossoms which had turned blue 
from the ammonia, became red again some time after their removal from 
the ammoniacal atmosphere. 

The spruce furnishes an example of the influence of the developmental 
stage on the amount of injury. The old needles took on a pitch black color 
and were retained, while the color tone of the young, delicate needles, at first 
a dirty green, later passed over into a faded, reddish yellow. The individual 
power of resistance in the different needles is shown especially clearly in an 
experiment in which some needles could be observed on branches, among 
the pitch black ones, which showed noi discoloration or at most only a 
darker green. The black color was due mainly to the pitch black color tone 
which the protoplasma of the epidermis and mesophyll cells had assumed. 
The cell walls were only slightly brown. In the cells most injured the 
contents had become a consistent, granular, doughy mass, which at times had 
drawn back from the walls. The contents of the guard cells of the stomata 
were also pitchy black, never red, as in injuries due to acids. In the transi- 
tional places between tissue which had remained healthy and that which had 
blackened, it was noticed that the protoplasmic mass in which the chloro- 
plasts were imbedded had already turned black, while these granules ap- 



1 Zeitschr. f. Pflanzenkrankh. 1893, p. 100. Lindau (loc. cit., p. 286) describes 
the action ol' the strongly concentrated ammonia gas on the plant cell; in the 
interior of the leaf the cells usually show very strong- plasmolysis; the contents 
become indistinct and at times diops of oil are exuded, in this a brown to black 
coloring- matter is given out which tinges the entire contracted contents. This 
proves later to be a ferment. 



732 

peared unchanged in form and position. Only later the green coloring 
matter in the protoplasm was found to have changed and become a dirty 
brownish green. Then the ground substances of the chloroplasts united 
with the other cell contents apparently leaving behind some granular 
remnants. 

The ammonia might also exercise some special poisonous effect on the 
cell contents besides combining with the acids as has been assumed in another 
place. Kny^ has already called attention to the fact that, according to the 
statements quoted in the hterature on this subject, the protoplasm in very 
different parts of the plant possesses an alkaline reaction without having 
influenced the chloroplasts. The same author has shown that a very dilute 
ammonia solution injures the assimilatory activity. 

In one case, where the wall of a stable was used as the back wall of a 
greenhouse, the way in which ammoniacal poisoning may often take place 
was clearly demonstrated. When the heat was turned on in the autumn, 
ammonium carbonate developed from the wall, which, in a short time, 
blackened the leaves of Aucuba, Viburnum Tinus, Primus Lauroccrasus, 
the Dracaenae and other plants in the greenhouse. Only the tissue immedi- 
ately adjoining the veins of the leaves remained green. 

Tar and Asphalt Fumes. 

The discoveries concerning the injuries of tar and asphalt fumes have 
been explained only recently, since the material for observation has become 
more abundant. Aside from the effect which the asphalting of streets can 
produce at times in sensitive plants, the factories preparing the carbons for 
arc lights are to be considered as essential causes of disease. 

Roses rich in tannic acid, strawberry leaves, Ampelopsis quinque folia 
and chestnuts should be named as the most important plants showing injury 
from asphalt fumes'-. Different varieties of roses suffer in very different 
degrees ; for example, Tea and Bengal Roses are less affected ; Remontants 
and their hybrids, however, are for the most part very severely attacked. 
Parts of the outer membrane, or the whole leaf surfaces become a dull black. 
Usually if the whole surface is not discolored (Fig. i68 la) the blackened 
places occur as interrupted or connected bands between the larger lateral 
ribs, that is, in the intercostal fields. If the sepals have been affected by 
the fumes, the blossom buds unfold only poorly. Soon after the appearance 
of the blackening, the contents of the epidermal cells of the upper side will 
be found deeply browned, granular and lumpy, and usually deposited along 
one of the horizontal walls. The cuticle is not browned and apparently 
unchanged. When the leaf is more diseased, the epidermis of the under 
side becomes affected in the same way and later collapses. On the other 
hand, the mesophyll is but little irritated. The fumes act only on the exposed 
surfaces of the organs; all the covered parts (Fig. i68 //;) remain un- 

1 Bot. Centralbl. 189S, Vol. LXXIII, p. 430. 

^ Sorauer, P. Die Beschadig:unscn der Vegetation durcli Asphaltdixmpfe 
Zeitsclir. f. I'flanzenkranldi. 1897, p. 10. 



733 







Fis'. IfiS. Vii-giniM ciecpci', strawberry and rose leaves injured by tar fumes. 



734 

changed. If the middle part of the leaf is injured, the edges curl up like 
the sides of a boat. 

Attention should be called in passing to the fact that in many roses 
(for example, Rosa turbinata), a similar discoloration appears in the late 
autumn. In this rose, for example, I found that the older leaves, still 
hanging on the stems, had become dully spotted with black without any 
previous red coloration ; this arose from the contraction and browning of 
the contents of the epidermal cells. These cells, however, retained their 
natural turgidity and height, but began to collapse after having been affected 
by asphalt fumes. In this the contents of the mesophyll also retain their 
normal consistency and position for some time, while, in the autumn colora- 
tion, they contract at once and change into uniform masses, at first green, 
but later turning brown. Under the microscope parasitic blackening 
( Aster oma radiosiim, etc.) can be distinguished easily from asphalt cor- 
rosion. 

Before I began my experiments, Alten and Jannicke^ had already 
described the blackening of roses and strawberries caused by the action of 
asphalt fumes. They considered the iron which was proved present in these 
fumes to be the actual injurious factor since it combined with the tannic 
acid of the cells and they supported this theory by experiments in which 
they produced black spots, corresponding to those in asphalt injuries, by 
sprinkling the leaves with ferrous chlorid and ferric sulphate. Ferric 
chlorid did not have this effect. 

I could not obtain this result and observers who have sprayed with iron 
solution as a means of overcoming chlorosis and icterus do not report any 
blackening. 

In the strawberry leaf illustrated in Fig. i68, 2 (a cultivated form of 
Fragaria chilcnsis), only a partial blackening of the upper side is found at 
g because only this part of the leaf had lain free; otherwise the phenomena 
were similar to those in roses, the curling of the leaf edges, the partial dry- 
ing of the leaf serrations, etc. 

In Fig. 168 J we see a leaf of Ampelopsis quinguefolia a few weeks after 
it had been acted upon by tar fumes from a factory making electric light 
carbons. The less diseased leaves were found to be still green but not out- 
spread ; the edges were curled up like bowls and the inside of the blade 
wrinkled by the outpushing of some of the tissue lying between the finer 
ramifications of the veins. At times small places with a cork colored upper 
surface were found near the midrib. With more extensive injury, these 
places were always present and passed over partially into blight spots which 
became dr>' and ultimately united. Finally, each leaf may show very regular 
markings due to the, drying of the intercostal fields. (Fig. 168 3s.) These 
dry places often break away, due to the rubbing of the leaves against one 
another, thus producing a lattice-like perforation (Fig. 168 3/). 



1 Alten, H., und Jannicke, W. Eine Schadigung von Rosenblattern durch 
Asphaltdampfe. Ref. Zeitschr. f. Pflanzenkrankli. 1S91, p. 156 und 1892, p. 33. 



Young branches become corky on the side affected and show fine cracks. 
Any existhig air roots dry up. 

When the action of the asphalt fumes ceases, the leaf's attempt to heal 
itself at once become apparent. In case the palisade parenchyma has been 
only a little, if any, affected, it may elongate somewhat and slightly push out 
the epidermis, which has collapsed to a state of irrccognizahility. If, how- 
ever, the palisade layer has also died the healthy underlying mesophyll 
develops a perfectly regular layer of flat cork cells. The same process may 
be noticed on the leaf stems : the brown, dead, ruptured, outer cork and 
parenchyma layers, together with the hard bast bundles which at times have 
also succumbed to the necrosis, are separated from the healthy tissue by a 
broad cork band which in extreme cases extends as far as the cambium. 

Vitis vinifera suffers sooner and more than does Ampelopsis, so that its 
leaves, at times, are curled entirely out of shape and perforated. In this it 
was observed that in places lightly affected the guard cells of the stomata 
had suffered first. Other plants behaved dift'erently ; in regard to these, 
reference must be made to my original work on the subject. The corrosion 
of the epidermal cells, however, may be cited as the universal characteristic. 

As in all injuries due to gaseous bodies, the fact that the injury is 
chronic, or acute, determines the results ; in the former case, with slower 
action, the organ affected can remain alive for some time by its counter 
action and may slowly live out its life. In this the characteristics differ 
from those found when the action is that of more highly concentrated gas 
waves, which result in a rapid death. Thus, for example, in the slow death 
of spruce needles, a strong, red discoloration of the cytoplasm of the guard 
cells and later, in fact, of their walls was perceived in the still green parts, 
but not if the injury was acute. The walls of the vascular bundles element 
also discolored ; as always happens from asphalt fumes, the cell walls suffer 
especially quickly. This is seen very well in the older fir needles which 
acquire a metallic lustre. 

Bromine. 

In the ordinary industries in which bromine is. produced injuries due 
to bromine alone may scarcely be spoken of because, as a rule, sulfurous 
acid works with it. At considerable distances from the factories the 
bromine may still be perceived by its odor, but no decided injuries from 
the acid. Therefore, any description of natural occurrences in the neigh- 
borhood of bromine factories may be omitted here and only the behavior of 
plants under the artificial action of intense bromine fumes be described. 
I carried out experiments as follows for 4 days : — ■ 

Small, well-rooted spruce saplings in pots were exposed several hours 
each day to gaseous bromine, being left out of doors between times. The 
branches nearest the bromine sources naturally suffered most and all their 
needles turned brown. On the less injured branches many needles were 
found to be partially brown from the tip back, while on the branches furthest 
away from the course of the bromine only a few brown needles were found 



• 736 

among the healthy ones. The red brown, which in the beginning was very 
bright, soon turned into a gray brown. The needles kept this color until 
they fell, about two weeks later, but' this took place only on greatly injured 
branches. It was found in the discolored places of the slightly injured 
needles, remaining on the branches, that the walls of some groups of meso- 
phyll cells near the epidermis had turned a faded to reddish yellow, while 
the contents had lost their color and finally with a complete disorganization 
of the walls had dried up. In this they not infrequently passed through a 
stage of foamy consistency. For some time after the action of the gas the 
guard cells of the stomata seemed to have become discolored up to the 
healthy tissues only in the zones of transition whereby their walls had turned 
a brownish yellow. The epidermis was slightly browned ; the sub-epidermal 
prosenchymatous fibres were found to be colorless. The mesophyll near 
the brown places remained green and had either a flocculent green content 
or the chloroplasts were united into lumps. Healthy tissue adjoined this 
immediately. 

At places more strongly injured the vascular bundles were also affected 
and discolored just as from sulfurous acid, but the color tone of the injured 
needles was only rarely a reddish brown. They were generally a yellowish 
brown and less hard, a fact distinguishing them from needles affected by 
SOy. The slight amount of difference is of less moment here because, as 
said above, in general injuries from bromine occur as a rule in connection 
with those caused by sulfurous acid. 



CHAPTER XVII. 



SOLID SUBSTANCES GIVEN OFF BY CHIMNEYS AND THE 
DISTILLATES THEY CONTAIN. 

The best survey of the material from the streams of smoke affecting 
vegetation is found in a table by W'islicenus^ which we may repeat here un- 
changed because it is so very clear. 

No general decision can be reached as to the substances given in this 
table. Under certain circumstances they may become injurious and, indeed, 
very injurious but, in other cases, they do not cause any loss of crops worth 
mentioning. This depends not only upon the greater or less exposure of 
the plants but also on locally different, secondary conditions. Aside from the 
individual sensitiveness of different species of plants, the constitution of the 
soil and the weather at times become decisive, especially with fine flying 
ashes. 

It should be mentioned in connection with the injuriousness of tar 
•vapor that tar vapors from lime kilns also cause injuries. In burning lime- 
stone, when the calcination begins, that is, the breaking down of the carbon- 
dioxid, the smoke becomes laden with great quantities of the distillates given 
in the table, which produce corrosions similar to those described under 
asphalt fumes. These vary with the plant. 

The injuriousness of soot was previously universally overestimated 
and is still, to some extent. The more recent investigations of v. Schmitz- 
Dumont and Wislicenus^ confirm Stockhardt's older discoveries, that soot 
is usually non-injurious. More delicate plants may show corrosion because 
of phenol, etc., carried in the soot. 

The theory of the stoppage of the stomata must be left undiscussed. 
According to my investigations of plants covered with soot the cases are 
very rare in which the soot particles have succeeded in getting into the 
cavities of the stomata, or actually have stopped them up, and even in these 
rare cases, I have not been able to perceive any change in the surrounding 
cells. Considerable quantities of extractive substances (sulfates and 
phenols) must first be leached out from the soot before any injury may be 



1 Wislicenus, H. Zur Beurteilung- und Abwehr von Rauclischaden, Vortrag 
in Dresden am 31 Mai 1901. Zeitschr. f. angewaridte Chemic 1901, Part 28, Taf. V. 



738 



CHEMICAL CONSTITUTION OF 



(THE FIGURES ITSTDICATE 



Distillates 

and Solid INIatter 

Contained 



Occurring Tyjiically 
in 



Constituents 

in Gases 
from Smoke 






9 if^ 



Ordinary 
Smoke from 

Hard-coal 

Furnaces 
(Double Chemical 

Air Content) 



o 



steam 
Boilers 



House 



Tar Fumes (Injurious) 
Aromatic Carhurotteil Hydro- 
gen 
Phenol ("Creosote") 
Anilin 
Pyridin 
Pyri:ol 



SooT (Practically Non-injurious) 
Carbon with Compounds: 

Tar-like, NH„ 

Potassium, Sodium, Calcium 

Sulfuric Acid 

Chlorin 

Rhodan, etc. 



Fi-Yi\G Ashes (Conditionally 
Injurious) 
Oxids ^ Various Bases as 

Carbonates I Non-injurious 
Phosphates [ Insoluble 
Silicates J Substances 
AsoOa Soluble with Difficulty 
Suffates I ofFe, ^ Soluble 
Chlorids J Zn, Cu i Injurious 
Alkalies and Am- f Sub- 
monia Salts J stances 



Other Specific Soi.ins: 
Zn and ZnO 
CaCa, Ca(OH),, CaCOa 
Cement Dust 



Ordinary 

Coke 
and Brick 

Ovens, 
Occasion- 
ally in 
Charcoal 

KHns 



T'nsnital)ly 

rsed, 

Ordinary 

Hard-coal 

Heating, 

Iron 

Retineries, 

Steel 

Smelters 

( Reducing 

Heat) 



Metal Refineries 



Zinc Refineries 
Carbid Factories 
Portland Cement Worl 









CO, 

(CO) 



HJ) 



SO, witli 

(SO., and) 

II. .SO. 



HCl 



CI 



HF 



SiF^ 
H,Si F, 



Nitric and 
Nitros Acids 



H..S 

(CSJ 



Nil:. 

(Amin Bases, 
Ammonia Salts ] 



Cyan ids 
Rliodanids 



Ether and 

Benzin 
Fumes, etc. 



77.41 

IM.i;; 

S.7:; 
(— ) 



■ 0. (»(;:; 



O.OOo 



79.5 

8.0 

12.5 
(-) 



0.1)4 



( ]Manufacture 


of 






(^Manufacture 


of 


(Manufacture of 



739 



VARIOUS KINDS OF SMOKE 



VOLUME PERCENTAGE) 



6 


7 


8 


9 


10 


11 


12 


13 


14 


15 


16 


17 


18 




.- ~ 




r. 

S t^ F~- 

- 9 C i; 




3 o 


"d.S 

(D o 


■1^ - — ^ 

:: X 

C X 

22; 


.5^? 

'^X. 

5 i 


X gct^ \ 




o 


22 

'-3 

13 


>^ 


f S 




lill 






2-1 

o - 
03,.= 


f3 £ 


■^ oi 




§11 


a; 




i 


p — 'r^ 


r— ^ 


^ .5 

■J. r/i ^f. 


03 &I 




So 


CO 


X G 

.2x 


1- 0^ 3 s 

Ph ^ '^ 

o 




1 


M 


81 










()8.44 












49.:5!» 




10 


L'.O 








S.iKi 

7.77 
(-) 

15.7 




• 








5.41 
(-) 
40.S(i 






Much ! 




8.5 
Used: 


I'll 


In 

Annealing 
U.I IS!) 














Ultra- 
marine 
Ovens 








0.4.5 




In 






0.(_)74 










o.o;!!» 








Fusing 

(1.44;; 














:!.o. . 0.5 
















0.02;; 












0.004 


























Chiefly 










1 


Waste 


1 1 


















Gases 
Containing 














Boric 






Fluorin 
















Acid 






11 XO:, 












Illuminating Gas, Soda Re 


^idue in 


Refuse ^ 


Heaps. ) 












Illuminating Gas, rru,«sic 


Aoi.l, Fe 


rrocyani 


d, etc.) 












Photographic Papers, etc. ) 





























740 

manifested. This is shown in Wislicenus' experiments with the soot from 
hard coal, Hgnite and benzine, as well as extracts from soot, by means of 
which the leaves of the hornbean and linden and, later also spruce needles 
were slightly etched. Probably, as they dry up, the salts effect an osmotic 
removal of w^ater and a drying of the cells. The same experiments also dis- 
pelled the fear that a thick coating of soot absorbs the light, changing it into 
heat and, therefore, acting disadvantageously. 

It is theoretically possible that the carbon dioxid carried in the smoke 
can act injuriously for even experiments with an extreme increase of this 
gas above the normal 0.04 to 0.06 per cent, have proved the retardation of 
assimilation but this can scarcely be spoken of in practical industry. The 
same holds good for carbonic oxid. 

The metallic elements of the smoke from smelters (see table) also enter 
into the question of the effect of flying ashes. According to Freytag's inves- 
tigations^, pure metalHc oxids are usually non-injurious. Naturally, foHage 
bearing such oxids cannot be used as food for animals, since they may easily 
cause inflammatory diseases. 

Also, these metallic elements such as insoluble oxids or carbonates and 
silicates scarcely injure the aerial parts of the plants more than does the 
street dust. Soluble compounds, on the other hand, such as arsenous acids, 
sulfates, and chlorides (copper, zinc, and lead) are principally concerned 
here and produce brown spots through the corrosion of the tissue, as soon as 
they are deposited on moist leaves. They are said not to injure dry foliage 
and a subsequent wetting from rain easily washes away the coating. Mer- 
cury fumes in the air always act very injuriously. The compounds washed 
into the soil by rain are absorbed by it and are usually non-injurious. A 
large accumulation of arsenic (more than o.i per cent.) is disadvantageous. 
Experiments made by Phillips- prove that healthy plants undergo no dis- 
turbances in growth from the taking up of lead and zinc, while copper acts 
as poisonously as arsenic and disturbs the root development. Klein^ and 
numerous, more recent observers furnish proof of the presence of arsenous 
acids in plants. Such poisoning of the soil may occur, for example, near 
copper smelters and in the litigation against the Mannsfeld-Hettstadter 
copper smelters Grouven refers especially to this point*. My own experi- 
ence in the same region shows that, at present, large surfaces of the fields 
have become poisoned and, despite very abundant fertilization, yield very 
meager harvests. The experiments in which soil which had become unfer- 
tile was carried from the vicinity of copper works to a region free from 
smoke prove that the gases in the smoke are not alone the injurious factors, 



1 Freytag, in Jahrb. ftir das Berg- unci Hiittenwesen im Konigreich Sachsen 
1873, pp. 24 and 36, cit. in Hasenclever. — Landwirtsch. Jahrb. 1882, p. 315-375. In 
reg-ard to the action of smoke, the author differs from Schi^oder inasmuch as he does 
not consider the sulfurous acid as sucli to be the injurious agent, but only the sul- 
furic acid which is being formed from it. 

2 Phillips. The absorption of Metallic Oxides by plants; cit. Bot. Centralbl. 
1SS3, Vol. XIII, No. 11, p. 364. 

3 Chemischer Ackersmann, 1875, Part 4. 

4 Fiihling's neue landwirtsch. Z. 1871, Part 7, p. 534. 



741 

but also the soil which has been rich in copper salts. Even in the latter 
place, which is free from smoke, the plants {Phase olus vulgaris) became 
diseased while those sown in the same region in soil which had always been 
there remained healthy and developed vigorously. 

An analysis of potatoes, of which the plants themselves were covered 
by the metallic dust from a nickel factory, shows how much of the metal 
may be taken up by the plants during one period of growth. The healthy 
foliage contained (in percentages of substances free from water and from 
sand) : 

Copper oxid 0.198 

Zinc oxid 0.169 

Nickel oxid 

The diseased foliage contained (in percentages of substances free from 
water and sand) : 

Copper oxid 0.0713 

Zinc oxid 0.1712 

Nickel oxid 0.0251 

Analyses of the tubers from these plants, however, did not give any 
zinc and nickel oxid, and only 0.0043 P^^ cent, of copper oxid as contrasted 
with healthy tubers which contained 0.0041 per cent^. 

Besides copper as a poison the arsenic compounds are important because 
of their injuriousness. According to v. Schroder these impair vegetation 
even if present in the soil in amounts of less than o.i per cent. 

Nevertheless, the improved technique of manufacture takes care that 
more and more of the arsenic, as well as the soluble metal salts, is kept back 
from the smoke in the flying dust flues, so that at present a fresh metallic 
poisoning of the soil is less to be feared. 

And yet the throwing off of flying ashes requires increased attention. A 
number of my own experiments have shown that with many flying ashes 
which become mixed with the soil a visible increase of growth may be 
obtained, while those from other industries have caused poisoning. This is 
less often a direct injury to the aerial parts of the plants, but more fre- 
quently an indirect one, manifesting itself by its effects on certain heavy 
kinds of soil, rich in water. In aerial injuries, sodium sidfid and caleium 
sulfid can produce corrosion in some, more tender plants. The course of 
the action in the indirect injuries has not yet been sufficiently explained. 
In my opinion, reduction phenomena in the soil are partially concerned in it 
by which hydrogen sulfid is developed. 

In heavy soils deeply covered by flying ashes, especially if they have 
been heavily fertilized with lime, a phenomenon of disease appears to such 
an extent in barley (I have called it "spotted necrosis") that the harvest is 
greatly reduced. All parts of the plants, even the beards of the glumes, 
appear closely stippled with brown. The brown points represent centers of 

1 Konig:, J. Denkschrift der Landwirtschaftl. Versuchsstation Miinster i. W. 
1896, p. 204. 



742 

dead tissue of which parasites certainly are not the cause. Black fungi 
may later infest these spots and then this complication is described as the 
"Horm'ondendron" disease. The spotted necrosis is, however, not a disease 
peculiar to regions of flying ashes but it undoubtedly occurs most inten- 
sively there. I found it could be lessened by a heavy application of lime. 

The opinions handed down by Steffeck^ give the best references to the 
injurious action of hydrogen sulfid. In them the repeated decrease in the 
value of the harvest by a mechanical coating of the soil is also considered. 
I also know of cases in which a deposition of ashes on vegetable plants, 
especially varieties of cabbage, was so heavy and could be removed to such 
a slight extent that the quality of the plants became poor, or they were abso- 
lutely unsalable. If fodder carrots and sugar beets had been heavily covered 
and their leaf heads used later as fodder some of the animals died. Incred- 
ibly large amounts of ashes were found in the stomachs of these animals. 

Hydrogen Sulfid. 

In consideration of our theory that hydrogen sulfid may be formed in 
certain heavy kinds of soil after flying ashes have been deposited on them, 
I made some experiments with barley. In some pots, pieces of potassium 
(poly sulfids) from sulphur liver were laid between the young barley plants ; 
in other they were put in the water in saucers in which the pots of barley 
stood. A piece of lead paper, laid between the plants, slowly turned brown. 
After six days the leaves began to turn yellow usually, in fact, beginning at 
the center, more rarely at the tip. The discolored areas appeared to be 
more watery and transparent than when the yellow discoloration was pro- 
duced by other causes^. A wilting of the tissue followed the yellow discol- 
oration and a drying of the green leaf surface lying above it, together with 
the assumption of a grayish yellow color. 

The first symptom of the disease is always the bleaching of the chloro- 
phyll coloring matter, which at once begins to spread into the cytoplasm. 
This is not preceded, nor accompanied, as in other cases of poisoning, by a 
contraction of the primordial pouch (or a shrivelling of the chloroplasts). 
Instead of this, in places, the passing over of the cell water into the inter- 
cellular spaces becomes noticeable, thereby explaining the transparent 
appearance of the yellowish areas. The outlines of the individual chloro- 
plasts then disappear up to the appearance of a granular mass which is 
contracted in the centre of the whole cloudy, pale yellowish, green cypto- 
plasm. The impression given is that here the cell contents as a whole swell 
up into an uniform, doughy mass, while in the action of the hydrochlorin 
and hydrochloric acid shrivelling phenomena are perceived and, with sul- 
furous acid, a process of drying of the contents which remain differentiated. 



1 Steffeck, Die dui'cli g-ewerbliche Einwiikung-en hervorg-erufenen Flurschaden 
und Verunreinigung-en von Wasserlaufen und Teichen. Magdeburger Zeitung 1907. 
Nos. 329 and 331. 

2 Sorauer, P. Beitrag zur anatomisclien Analyse rauchbeschiidlgter I'flanzen. 
Landwirtsch. Jahrb. 1904, p. 643. 



743 

In oats the bleaching of the chlorophyll coloring matter was slower and less 
intensive. As a result of the subsequent diseased condition of the roots, 
the walls of the vascular bundle elements became a deep brown. 

Soda Dust. 

Ebermayer^ has reported on the injuriousness of sodium fumes. In 
the manufacture of cellulose, sodium lye, under high pressure, is permitted 
to act on pulverized pine wood. To get back the sodium, the lye used is 
vaporized and the residue burned to destroy the organic substances. In 
this 'way a considerable amount of sodium carbonate is freed in the air. The 
leaves of fruit trees near such factories appear brown or black and die after 
a short time. 

Leaves which had been dipped into a dilute sodium solution (i.oi 
specific gravity) took on the same color; apple leaves appeared to be some- 
what less resistant than pears and plums. 

In regard to soda dust, as yet only those cases have been known in 
which soda from ammonium soda factories was turned to dust by an 
improper method of ventilating the factory rooms. The soda dissolved by 
dew, or rain, easily produced in many trees an appearance of the injury from 
acid vapor, such as the dying of the edges of the leaves, or scattered cor- 
roded areas. 

In doubtful cases the expert is helped by the condition in wild grasses 
and especially grain stalks which assume a lemon yellow color. Grain can 
become sterile according to the time and intensity of the giving ofif of the 
soda dust and trees may gradually be killed by the repeated annual injury 
to their leaves. Besides this, different plant species vary greatly in sensi- 
tiveness and often are resistant to soda but sensitive to acid smoke, or 
conversely. My experiments on grain and wild grasses (Agropyrum 
re pens, Agrostis vulgaris, Lolium, etc.), in which I covered them with dust 
while wet with dew, gave the same yellow discoloration, even in the glumes, 
just as in natural injuries'- which were demonstrable at a distance of 2 kilo- 
meters from the factory. Konig'' observed that the edges of barley leaves 
became white. Red clover is said at first to show small black spots on the 
leaves, some of which later become entirely black and drop ofif. The same 
is true of potatoes. Konig found perforations near the brown edges of the 
leaves in oaks as in cherries. The needles of the white fir are said to 
become yellow at the tip and fall ofif. As a result of his analyses, Konig 
considers the action of the soda to lie not only in a humification of the leaf 
substances, but also in the taking up of soda by the leaves, from which it 
wanders down to the roots. An increase in acids, especially silicic and 
sulfuric acids, takes place at the same time with the increase of the amounts 



1 Ein Beitrag zur Pathologie der Obstbaume. Tagrebl. d. Naturf. — Ver.s. zu 
Hamburg-, cit. Hiedermann's Centralbl. 1S77, II, p. 318. 

2 Zeitsch. f. Pflanzenkrankh. 1S92, p. 154, note. 

3 Borner, Haselhoff and Konig-. tJber die Schadlichkeit von Sodastaub und 
Ammoniakgari auf die Veg-etation. Mitg-eteilt von Konig, Landwirtsch. Jalirb. XXI, 
cit. Zeitsch. f. I'flanzenkrankh. 1893, p. 98. 



744 

of sodium\ Often the phosphoric acid and chlorin also increase. In the 
injuries due to acid gases this reaction of the plant body is shown also 
further by the fact that the leaves, not yet injured beyond a certain extent, 
contain more bases than do healthy ones. 

Control Plants. 

Reference must be made to technical handbooks for technical regula- 
tions regarding the avoidance or decrease of injuries due to smoke and 
flying ashes. However, I would like to give here one method in clearing 
up the question whether the injuries already perceived are connected with 
the poisoning of the soil, or are due to the purely aerial action of gas waves 
containing acid. This method is that of control plant cultivation and is 
carried out as follows : Wooden cases, containing at least one cubic meter, 
are sunk in the fields in question and are filled with soil which, before 
witnesses, has been taken from a region free from smoke. On the other 
hand, soil taken from the fields in question is put in similar cases which are 
sunk in a field in a region free from smoke. Both series of cases are then 
sown in the same way with beans (Phaseolus vulgaris nanus) and harvested 
simultaneously after a number of weeks. The harvest is examined micro- 
scopically and chemically. 

The poisoning of the soil is proved by the fact that the plants grown 
in the soil taken from the fields in question but kept in cases in regions free 
from smoke become diseased with the same characteristics as those near the 
source of smoke. If, on the other hand, the beans from the cases filled 
with soil from a region free from smoke which had been sunk in the fields 
in question, near the injurious industrial establishment, show the charac- 
teristics of smoke poisoning, this then proves that the dangerous streams of 
smoke alone are sufficient to injure vegetation. 

These comparative cultures have the advantage of giving the contesting 
parties an insight into the kind of injury which is recognizable to the layman 
and thereby furnish the means of an unification of opinion, thus avoiding 
lengthy lawsuits. It is well in regard to these to strive for the formation of 
federal smoke commissions. We mean by this the appointed persons from 
among botanists, chemists, agriculturalists and foresters, who would meet 
together as a commission of specialists and would always be the same for 
the different districts. By retaining the same persons they would have a 
more exact insight into the special conditions of their districts and a more 
assured judgment in these difficult questions. 

Illuminating Gas and Acetylene. 
The injurious effect which illuminating gas exerts on plants has been 
ascribed to the hydrogen sulfid abundantly present in it. This is, how- 
ever, not the only cause, for Kny- has shown that gas, carefully purified 

1 Konig (Denkschrift 1S96, P. 207), found only in rye, despite a higher sodium 
content, a smaller ash, and especially less silicic acid. It seemed to him that the 
silicic acid was dissolved by the soda in the glume and then washed away. 

- Sitzungsber. d. Ges. naturl'orsch. Freunde zu Berlin in But. Zeit. 1871, p. S69. 



745 

from hydrogen, is still injurious to roots. I conclude from the violet gray 
color in many roots of trees injured by illuminating gas that some of the 
tars, or the ammonia, carried over in the gas are the injurious factors. For 
the present, this violet discoloration of the roots may be considered the best 
indication of the injury even if it is not an absolutely certain one. We must 
agree with Wehmer^ that such root discolorations occur also in death due to 
other causes and that often in trees killed by illuminating gas in the soil 
this characteristic is found only sparingly. The later case is easily explained 
since only those roots discolor which come in direct contact with the injuri- 
ous agent and thus cause the death of the tree. The root dying subsequently 
remains uncolored. 

The different trees and shrubs show a great diversity in their power of 
resistance to the affect of gases. While in Kny's experiments, for example, 
the elm died very soon, Cornus sanguinea withstood the poisoning of illum- 
inating gas without any perceptible injury. An analysis made by Girardin- 
shows how far the effect of a gas pipe may extend. According to it, the 
soil at the distance of one meter showed empyreumatic oils and sulfur and 
ammonium compounds. 

A further example of the different behavior of plants toward illumin- 
ating gas is given by Lackner^. His observations, however, relate to the 
effect which the gas is said to exert when burned in the room. Retention in 
a room where much gas is burned is very injurious to camilleas and azaleas 
and ivy is said to die at once. On the other hand, palms. Dracaenae, 
Aucuba japonica and other plants are found to be not at all sensitive to it. 

Richter's experiments* prove that illuminating gas acts arrestingly on 
the growth in length of bean seedlings and other plants and favors the 
growth in thickness. It is not true that the amount of carbon dioxid, rapidly 
increasing by combustion, acts as injuriously on the plant body as on the 
animal body, as people were inclined to assume^ ; it is rather to be supposed 
that different products of incomplete combustion of the illuminating sub- 
stances should be to blame for this. 



1 Wehmer, C. tjber einen Fall intensiver Schadignng' einer AUee durch aus- 
stromendes Leuchtgas. Zeitschr. f. Pflanzenkrankh. 1900, p. 267. 
^ Jahresber. iitaer Agrikulturchernie Jahrg. VII, 1S66, p. 199. 

3 Monatsschrift d. Ver. z. Beford. d. Gartenbaues in d. Kgl. Preuss. Staaten. 
January, 1873, p. 22. 

4 Richter, O. Pflanzenwachstum und Laboratoriumsluft. Ber. d. D. Bot. Ges 
1903, Part. 3. 

5 We repeat that with otherwise favorable conditions for growth, the presence 
of carbon dioxid up to a high percentage is useful, since it advances the production 
of plant substance as shown by the increased elimination of oxygen. According to 
the investigations of Godlewski ("Abhanglgkeit der SauerstofCausscheidung der 
Blatter von dem Kohlensauregehalt der Luft" in Sachs' Arbeiten des bot. Inst, of 
Wurzburg, 1873, III, p. 343-70) the optimum for the carbon dioxid content lies 
tremendously high (5 to 10%) in comparison with the content of the air. In this 
way is explained the favorable action of hot beds and of the low sunken glass houses 
of the gardener warmed with horse manure. Here the high carbon dioxid produc- 
tion of the organic substances, which are being decomposed, is united with the 
abundant development of heat, weakened light and moist air; i. e. the factors 
essential for a luxuriant leaf growth. But blossom development is promoted, how- 
ever, since with the increased carbon dioxid content of the air, the blossoms are 
formed earlier and more abundantly. (Demoussy, tJber die "Vegetation in kohlen- 
siiurereichen Atmospharen. Compt. rend. 1904, Vol. 139, p. 883). 



746 

According to my experience with house plants, the dryness of the air 
is primarily the chief cause of death, and manifests itself in the drying of 
the leaf tips and edges. 

In regard to the effect of illuminating gas on roots, Bohm's experi- 
ments\ with willow cuttings in bottles of water through which illuminating 
gas was passed, showed that the action was slowly fatal. The cuttings 
which died after 3 months had formed new short roots at the expense of 
the stored starch. The action was thus less intensive than it was when carbon 
dioxid was passed through the water. In this case all formation of new 
structures by the submerged stem was suppressed while the upper part, 
which formed tyloses in its ducts, developed sickly shoots. Death occurred 
after 2 months. In other experiments in which hydrogen was passed 
through the water, development was practically normal. (Compare the 
section on Excess of Carbon Dioxid.) 

The plants also died when illuminating gas was introduced into the 
earth in their pots. Seeds, set in earth through which illuminating gas had 
passed for almost 2^ years, developed more poorly. If a stream of atmos- 
pheric air was drawn through such soils for a considerable time, the soil did 
not lose its injurious effect entirely so that, as already stated, this effect may 
indeed be ascribed chiefly to the tarry products which are deposited in the 
soil in a fluid or solid form. 

Spath and Meyer- found that even a comparatively small amount of gas 
(25 cu. ft. distributed daily on 14.19 sq. m. at a depth of 1.25 m.) killed the 
roots which came in contact with it. Even a greater quantity of gas was 
found to be less injurious if it reached the trees during their winter dormant 
period. Here too different varieties of trees display a different power of 
resistance. 

Most expedient at present seems to be Juergens' method, as recom- 
mended by Bohm, of laying the gas pipes through the streets, etc., in glazed 
terra cotta pipes which have openings leading to the light standards so that 
constant ventilation can take place within the terra cotta pipes. 

Brizi'' has made experiments in regard to Acetylene poisoning. He 
found in one Italian city that Quercus Ilex died when growing alongside a 
pipe carrying this gas. Herbaceous plants died in pots and dried up if 
acetylene was introduced into the soil. The nuclei disappeared in the pali- 
sade cells of Coleus, the roots lost their hairs, the lateral roots seemed wilted, 
crushed and brown, the bark cells lacked all fluids. In Evonymous Japonica 
the plants in dry soil seemed perfectly normal after 7 days, while, in moist 
earth they had all dropped their leaves after the 6th day and most of the 
young roots had died. The laurel and the grapevine behaved similarly. 



1 tjber den Einfluss des Leuchtg-ases auf die Veg-etation. Sitzungsber d. k. 
Akad. d. Wissench. zu Wein, Vol. LXVIII B. 

2 Spath and Meyer, Beobachtung-en iiber den Einfluss des Leuchtgases auf die 
Vegetation von Baumen. Landwirtscli. Versuclisstat. 1873, p. 336. 

3 Biizi, U. Sulle alterazioni prodotte alle piante coltivate dalle principal! 
emanazioni gasose degli stabilimente industrial!. Staz. sperim. agrar. ital. XXXVI; 
cit. Zeitschr. f. Pflanzenkrankh. 1904, p. 160. 



747 

Brizi considers the action of the gases contained in the acetylene and the 
admixtures to be a displacement of the normal air, containing oxygen, so 
that the roots suffocated and he thinks that illuminating gas will act similarly 
but more powerfully. The moisture in the soil, therefore, favors the injury 
because it reduces the imperviousness of the soil to the gas. This theory of 
Brizi's of the suffocating effect on the roots exercised by illuminating gas, 
together with the products its contains, finds support in so far that I have 
perceived clearly the odor of butyric acid when cutting the roots of lindens 
in Berlin after poisoning from gas and I could determine a violet brown 
discoloration of the membrane of roots of trees which had died because of 
stagnant water. » 



CHAPTER XVIII. 



WASTE WATER. 



Water Containing Sodium Chlorid. 

Of all the injuries caused by waste water, the most common are those 
produced by sodium chlorid. These are found especially in regions where 
extensive hard coal mining takes place. From the experiments published 
by Konig^ in association with Storp-, Bohmer,"* Stood* and Haselhoff-"', we 
will quote a few figures about the composition of mine water which will 
suffice to show what quantities of sodium chlorid and other salts are con- 
tained in it at times. It contains per litre 

Name of Mining Sodium Calcium Magnesium Potassium Magnesium 

Company chlorid chlorid chlorid sulfate sulfate 

Levin 65.949 g 11.056 g 3.736 g 0.659 g — 

Matthias Stinnes.. 33-244 g 3-631 g 1-735 g — 0.042 g 

Saline Konigsborn. 45.413 g 4-o6i g 0.189 g — 1-256 g 

From these examples it is easy to reckon the effect of irrigating, or 
flooding land with such solutions. The action will be direct, as well as 
indirect, according to the changes which the soil undergoes. In the latter 
connection, the fact that nutrient substances in the soil (Potassium, calcium, 
magnesium, and, under certain circumstances, also phosphoric acid) are 
dissolved in increased amounts and washed away should receive first consid- 
eration. This leaching process begins with the percentage of 0.5 g. sodium 
chlorid per litre. Nevertheless, all water containing any considerable 
amount is dangerous for irrigation. Pot experiments with meadow grass 
show a considerable reduction in harvested substances corresponding to the 
loss in nutrition of the soil. 

A second disadvantage of irrigation with water containing sodium 
chlorid is the increased density of the soil. Even 0.41 per cent, sodium 



Die landwirtsch Versuchsstat. Miinster i. W. Donkschrlft 1S96, p. I.'jS. 

I^andwirtsch. Jahrbiicher 1883, XII, p. 795. 

Ibid, p. 897. 

Landwirtsch, Versuchsstat. 1899, P. 113. 

Landwirtsch. .Tahrbiicher 1893, p. 845. 



749 

chlorid in the soil is enough to make it sterile because of the density. Sanna^ 
found near salt works a preponderance of fine earth over coarse particles and 
calls attention to the fact that the work of the soil bacteria is stopped by 
the decreased supply of air. Such soils must unquestionably be laid open in 
furrows before winter so that they may again undergo a breaking up by 
frost. Finally, one more point must be cited to which Preglion" has called 
attention. He studied the peculiar deforming of the ears which is called 
"Garbin", and ascribed to the action of sea winds. According to him, how- 
ever, physiological drought is to blame for this. The salty soil holds the 
water so fast that the roots ^are not able to take it up in sufficient amounts. 

In regard to the direct effect, consideration must be given to the fact 
that a plant can particularly adjust itself to water containing salt, according 
to its own peculiarity, and change its habit of growth accordingly. Hoster- 
mann^ has proved that meadow grasses take on a xerophyte structure ; they 
become smaller and squattier ; the internodes shorter and the leaves smaller ; 
the plant growth is meagre and the root system develops weakly. Transpi- 
ration retrogresses and the energy of assimilation is arrested with 0.05 per 
cent. In regard to the germinating power of seeds, it has been observed 
that weak concentrations (0.5 to 0.75 per cent.) act favorably, but above 
that amount injury sets in. 

Areschoug* mentions other phenomena of adjustment, since he considers 
the retention of water in tissues not directly connected with assimilation 
(storage tracheids, slime cells) to be a protection against the accumulation of 
chlorids. Also, the hydathodes appear to eliminate water containing sodium 
chlorid. Diels^ found that structural adjustment for arresting transpiration 
increases with the saltiness of the habitat. It might be concluded from this 
that vegetation from the coast would also behave differently in basins of 
water containing different amounts of salts. Rostrup*^ also actually calls atten- 
tion to this point. Pines suffer the most and birches the least. It is evident 
from the notes made by the Economic Society of the Province of Maribo 
after the floods of 1858, '63, '65 that the effect of salt water is greater the 
more loam the soil contains. Of winter plants thus flooded, rye suffered more 
than wheat. In early spring seeding on land saturated with salt, barley and 
peas were injured most of all. Mangelwurzels, potatoes, white clover and 
ray grass did not seem to suft'er very much from the effect of salty soil. On 
the other hand, red clover was very sensitive. In Wohltmann's experi- 



1 Sanna, A., Einfluss des Seesalzes auf die Pflanzen. Staz. sperim. XXXVII; cit. 
Centralbl. f. Agrikulturchemie 1904, p. 826. 

2 Peg-lion, V, Dei' Salzgehalt des Bodens und seine Wirkung auf die Vegetation 
des Getreides. Staz. speriment agrar. ital. 1903; cit. Centralbl. f. Agrikulturchemie 
1904, p. 507. Ricome, Influence du chlorure de Sodium, etc.; cit. Zeitschrift fiJr 
Pflanzenkrankh. 1904, p. 222. 

3 Hostermann, Einfluss des Kochsalzes auf die Vegetation von Wiesengrasern. 
Landwirtsch. Jahrb. Suppl. 1901; cit. Centralbl. f. Agrikulturchemie 1903, p. 211. 

4 Areschoug, F. W. Untersuchungen uber den Blattbau der Mangrovepflanzen. 
Bibl. bot. 1902; cit. Bot. Jahresber. 1902, II, p. 295. 

5 Diels, L. Stoffwechsel und Struktur der Halophyten; cit. Bot. Jahresber. 
1898, I, p. 606. 

6 Rostrup, Plantepatologi, p. 74, 75. 



750 

ments^ with artificial sodium chlorid fertilization, barley and wheat (among 
summer grains) showed great sensitiveness, while winter wheat throve fairly 
well even with heavy additions of salt. Peas failed entirely with a strong 
fertilization; oats were more resistent. Winter rye was found to be the 
least sensitive. In potatoes, the starch content was much decreased ; the 
protein content not affected; the amount of ash increased. In sugar and 
fodder beets the quantity harvested was increased without a decrease of the 
sugar content. Their descent from coast plants may be noticed in this. 

The effect of salty soil manifests itself in trees only after they have 
stored up the salt for some time. Weber- is an advocate of the theory that, 
in many cases, it is not the excess of salt but the marshiness of the soil which 
causes death. He found in the yellowed branches of Salix viniinalis in the 
valley of the Lahn near Bersenbruck, where the mine water flows in from 
Eversburg, that the leaves had a chlorid content of 1.309 per cent., while 
those of healthy plants contained only 0.877 P^r cent. We find abundant 
statements concerning the behavior of decorative plants in Otto's book"*. He 
gives, as a universal characteristic, the reddening of the tips of plants before 
they die. 

Aside from mine water, a high content of sodium chlorid manifests itself 
in the sewage fields. In summer the concentration of the liquid sewage 
becomes relatively large and many plants are found "to scorch" as the 
gardener on such fields says. Tobacco has proved to be very sensitive so 
that up to the present there has been a complete failure of the tobacco crops, 
as emphasized by Ehrenberg*, who has considered very thoroughly all the 
injuries due to liquid sewage. 

Besides the sodium chlorid the amount of magnesium chlorid also comes 
under consideration. The effects of the leaching action are changed, as the 
experiments of Fricke, Haselhoff, and Konig^ have proved. While irriga- 
tion with water containing sodium chlorid results in an increased removal 
of calcium, magnesium, and potassium, yet from water containing mag- 
nesium chlorid, the calcium, potassium and sodium are lost and the mag- 
nesium is retained. In irrigation with water containing calcium chlorid, the 
calcium will be retained by the soil and plants, while considerable amounts of 
magnesium, potassium and sodium are lost. 

In large cities, however, the question of injury from sodium chlorid has 
still a different side, that is, in its use in thawing street railways. Besides 
this, coarse salt is strewn on the pavements by many householders. In 
Berlin, this is forbidden, to be sure, but the police is often deceived by the 



1 Wohltmann, F. Die Wirkung der Kochsalzdiing-ung auf un.sere Peldfriichte. 
I^andw. Zeit. f. d. Rheinprovinz 1904, p. 46. 

2 Weber, C. Kritische Bemerkungen usw.; cit. Bot. Jahresber. 1S98, II, p. 301. 

3 Otto, R. tJber durch kochsalzhaltiges Wasser verursachte Pflanzenschadi- 
giingen. Zeitsch. f. Pflanzenkrankb. 1904, p. 136. 

4 Ehrenberg, ]'aul, Einige Beobachtungen uber Pflanzenschadigungen diirch 
Spiiljauchenberieselung. Zeitschr. f. Pflanzenkrankb. 1906, p. 193. 

s Pricke, Haselhoff, E., u. Kimig, .!., tJber die Veriinderungen und Wirkungen 
des Rieselwassers. Landwirtsch. Jahrlnicher 1893, p. 801. 



751 

mixing of salt with sand^ The salt used to remove the snow melts and 
passes into the soil where the street is not asphalted. In the spring the trees 
start to grow but die during the course of the summer. Here, too, the 
different varieties display dift"erent degrees of resistance-. Besides this, the 
action of a solution of sodium chlorid varies according to whether it is con- 
stantly sprinkled on the roots or whether the soil dries out between times. 
The latter case is the more dangerous one. 

Extensive injuries have also been found near volcanoes due to the effect 
of the vapors. The sulfurous acid occurring in varying amounts in the 
vapor mixture, and also the hydrochloric acid and hydrogen sulfid, may well 
be the chief causes of the poisoning. They might also give rise to the 
destructive effect of the shoivers of ashes; yet this has been ascribed also by 
some observers to the extensively deposited sodium chlorid. According to 
Pasquale's reports", some of the red and violet colors of blossoms change to 
blue (Papaver, Rosa and Gladiolus), some remain unchanged (Viola tri- 
color. Convolvulus, Digitalis). The green parts of the plants become brown, 
during a fall of ashes occurring at the time the trees begin to grow, just as 
after burning or drying but not scalding. Succulent and leathery leaves did 
not suffer. Mechanical effects from the showers of ashes, such as a possible 
stoppage of the stomata, could not be confirmed immediately. They seemed, 
however, to make themselves felt after some days. 

Sprenger*, who describes the results of the Vesuvius eruption in April, 
1906, advocates the same theory as does Pasquale. 

Waste Water Containing Calcium Chlorid and Magnesium Chlorid. 

These are found abundantly in mine water from hard coal mines, in the 
mother liquor flowing away from salt works and baths, in factories preparing 
calcium chlorid, and potassium salts, in the waste waters of ammonium 
sodium factories, etc. The analysis of the neutral fluid, which flows from 
the kettles to which the ammonium chlorid obtained in the manufacture of 
ammonium sodium is decomposed, shows, for example, what amounts come 
under consideration in these cases. Konig^ found in i liter, 80.06 g. of 
sodium chlorid, 56.00 g. calcium chlorid, 1.02 g. sodium sulfate. In other 
tests, which were strongly alkaline, less of the substances named were found, 
but, in place of these, sodium sulfate and 3 to 5 g. of free calcium. The 
changes in composition in the soil have already been considered in the pre- 
vious section, but it should still be emphasized here that favorable eff"ects 
have been observed if weak amounts are given temporarily (up to 2.0 g. per 
liter). The germination of seeds was increased. Raspberries and straw- 



1 Weiss, A. Zeitsch. f. Gartenbau und Gartenkunst. 1894, No. 37. 

2 Ritzema Bos, Schadlichkeit des Aut'tauens der Tranibahnlinien mit Salz- 
wasser fiir die in der Nahe stehenden Baume. Tijdschrift over Plantenziekten 
1898, p. 1. 

3 Pasquale, Di alcuni effetti delta caduta di cenere, ttc. Bot. Zeit. 1872, p. 729. 
1 Spreng-er, C, Vegetation und vulkanische Asche. Osterreich. Gartenzeitung 

1906, Vol. VII. 

5 Denkschrift, p. 161. 



752 

berries were found to be very large and brightly colored on the soil saturated 
with calcium chlorid. The fruit, however, tasted of calcium chlorid and 
did not keep welF. 

Barium Chlorid. 

This is a comparatively less important element, which is found only at 
times in the waste waters of hard coal mines. Its poisonous action has been 
proved by Haselhoff" in water cultures of maise and horsebeans. Growth in 
height was arrested ; the leaves wilted and fell. In nature, however, direct 
injury will occur only rarely, because the sulfurous salts rapidly transform 
it into insoluble and non-injurious barium sulfate. 

Waste Water Containing Zinc Sulfate. 

Konig'^ has paid especial attention to the investigations of such waters 
from Zinc Blend Mines. It was proved that the brooks which take up the 
waste water contained sulfurous sine oxide in solution. An evident retro- 
gression in the yield and in places a very poor growth was noticed on 
meadows thus watered. The grasses grown on such sterile places, as well 
as the deformed, bushy beech and maple trees, contained up to 2.78 per cent, 
of their ash in zinc, while the ash of normal meadow plants did not contain 
this metal. Vegetation dies in places where zinc ore happens to be deposited 
accidentally. Only one specific zinc plant (the "white mineral blossom") 
was still visible. This "mineral copper blossom" contained not less than 1 1 
to 15 per cent, zinc oxid in its ash. It is thus seen how differently the 
various plants behave and what high concentrations may often be endured. 
The injuries appear only after a considerable number of years, after the 
zinc oxid present in very small amounts in the water of the brook has accu- 
mulated to considerable quantities. Konig is justified in concluding from 
this that the requirement made upon mines by the Concession Department 
that only clear water be allowed to flow away into the streams is not enough 
protection to the owners of meadows. 

The books supplement the discoveries mentioned, one of which by 
A. Baumann* treats exclusively of the effects of zinc salts on plants and soil ; 
while another, by Nobbe, Bassler and WilP takes up injuries due to arsenic 
and lead as well as zinc. 

It must be emphasized, from the results of Baumann's experiments, that 
the zinc sulfate in solution is much more injurious to plants than had been 
supposed up to that time. Small amounts (possibly .1% zinc, that is, 4.4 mg. 
zinc vitriol in a litre) have been proved absolutely non-injurious in all the 
plants under experimentation (13 species from 7 families) with the excep- 

1 Denkschrift, p. 161. 

2 Landwirtsch Jahrbiicher 1895, p. 962. 

3 Konig:, Untersuchungen tiber Beschadig-ungen von Boden u. Pflanzen durch 
industrielle Abflusswasser und Gase; cit. in Biedermann's Centralbl. 1879, p. 564. 

4 Baumann, A., Das Verhalten von Zinksalzen gegen Pflanzen und im Boden. 
Preisschrift 1884. Landwirtsch. Versuchsstat. VoL XXXI, Part 1, p. 1. 

5 Nobbe, Bassler und Will, Untersuchungen liber die Giftwirkung des Arsen, 
Blei und Zink im pflanzlichen Organismus. Landwirtsch. Versuchsstat. Vol. XXX, 
Parts 5 and 6. 



753 

tion of the radish. Conifers are very resistent. They withstood a solution 
containing i per cent, zinc while the Angiosperms died with even 5 mg. zinc 
per Htre and, indeed, older plants died in general more quickly than did 
young ones. 

The effect of the poison manifests itself by a striking change in color of 
the diseased plants. Scattered small areas of a metallic lustre on a rusty 
yellow color appear on the leaves and finally spread over the whole surface. 
The fact that the zinc attacks the chlorophyll apparatus especially, thereby 
hindering the work of assimilation, is proved by the observation that seed- 
lings in which the chlorophyll grains are not yet matured as well as plants 
grown in the dark and fungi behave indifferently to relatively highly con- 
centrated zinc solutions. 

Zinc carbonate and zinc sulfate placed in the soil exercise an injurious 
effect. In themselves, to be sure, they are not injurious although they are 
soluble in pretty considerable amounts in water containing carbon dioxid, 
whereby the zinc sulfid is first changed to zinc carbonate. But their dan- 
gerous action lies in the transformation which the zinc undergoes in the 
form of vitriol with the potassium, calcium, and magnesium salts. In this 
these nutrient substances become soluble and may be wasted away. In poor 
sandy soils sterility may, indeed, be produced and the injuriousness of irri- 
gation with waste water from zinc smelters lies especially in this removal of 
the nutrient substances. 

The injurious solubility of zinc in the soil depends essentially on the 
amount of calcium carbonate contained in it. In the presence of this min- 
eral to possibly four times the amount of the zinc sulfid no more zinc will 
be dissolved. A soil ruined by zinc sulfate can be improved by the addition 
of substances which render the soluble zinc salts insoluble. Humus has 
been proved to be splendid and, on this account, fertilization with moor soil 
can be recommended. In the absence of this, abundant stable manure, clay 
or marl may be used. Marl, or calcium, must be given under all conditions.' 
Tschirch mentions, in regard to injuries due to lead salts, that a peculiar 
kmd of dwarfing is produced. The plants which have received i kg. mennig 
(red oxid of lead) to 2 sqm. of surface remain small and do not bloom (lead- 
nanism) \ Devaux- found that lead solutions in a dilution of 1-10,000,000 
acted injuriously. This metal was fixed by the cell wall and contents. 

To purify waters containing zinc sulfate, the use of filtering layers of 
limestone dust and moor earth could be recommended; insoluble carbonic 
and humic zinc oxid is formed in them. 

Water Containing Iron Sulfate. 
The waste water from mines and washeries of sulfur silicate and from 
hard coal m ines, the water which drains from piles of hard coal culm and 

StuttgaTri893^.^EnS^' ^"^''^ "°™ Standpunkt der gerichtlichen Chemie usw. 

.raJ* ^^^^"^' ^e I'absorption des poisons metalliques tres dilues par les ceIliilP<, 
vegetaux. Compt. rend. 1901, cit Just's Jahresber. 1902. II, p. 353 cellules 



754 

the waste water from wire factories usually contains iron sulfate. Besides 
this, the use of ferrous sulfate as a disinfectant in cesspools should also be 
taken into consideration. Large amounts of iron sulfid are thus produced 
which, through oxidation in the air, are transformed into iron sulfate and 
sulfurous iron oxid. 

The ferrous oxid, like zinc from zinc sulfate, is retained by the soil and 
changed to ferric oxid, while a corresponding quantity of other bases, such 
as calcium, magnesium, and potassium, combine with the sulfuric acid and 
are easily washed away. This impoverishment of the soil is accompanied by 
an increase of magnetic oxid which initiates a souring and choking of the 
ground. As soon as the bases for the transformation of the iron sulfate are 
exhausted, the ferrous sulfate remains untransposed, or appears also as free 
sulfuric acid. 

However useful small amounts may be on rich soils (up to 150 kg. per 
hectare, according to Konig^), since the sulfuric acid, thus set free, must act 
as a loosening medium, just as injurious will be a continued addition of iron 
sulfate with constant irrigation of pastures. Experiments show that if acid 
compounds are given the plants instead of the basic salts which alone favor 
their growth (iron sulfate is strongly acid) a deterioration of the hay results 
and a decrease in the yield of milk. The different clovers and sweet grasses 
(possibly with the exception of Glyccria fluitans) disappear gradually from 
such pastures and sour grasses, the horsetails (Equisetum) and mosses take 
possession of the soil. An addition of lime water causes the eUmination of 
ferrous hydroxid with the formation of gypsum and it will thus be possible 
to purify waste water containing iron sulfate by the use of calcium. 

Waste Water Containing Copper Sulfate and Copper Nitrate. 

Waste water from silver factories and brass foundries is concerned 
here. An insight into the composition of such water is given by an analysis 
of solutions flowing from a brass foundry published by Haselhoff-. He 
found in one liter : 

Copper sulfate, 51.619 g; Copper nitrate, 5.298 g; Zinc sulfate, 14.045 g; 
Ferrous sulfate, 2.422 g; Calcium sulfate, 1.943 g; Magnesum sulfate, 
0.459 g; ^nd free Sulfuric acid (SO3), 30,376 g. This is, at any rate, a 
very extreme case, for it is one hundred times greater in the individual 
elements than is the content of the water which flows from copper works 
and silver factories. For the nature of the injury, however, the amount of 
the elements is unimportant, since small quantities produce the same efifect 
when used in continual irrigation. The way in which the sulfate and nitrate 
of the copper salts act on the soil is the same as with zinc and iron salts. 
Copper oxid is retained in the soil and remains chiefly in the upper surface 
of the pasture land. The sulfuric acid, which is set free, combines with the 
calcium, magnesium, and potassium, and these salts, with irrigation, pass 



Donkschrift, p. 175. 

Haselhoff, Landwirtsch. Jahrb. 1892, p. 263 and 1893, p. 848. Denksch., p. 17C. 



into the subsoil. Aside from tlie impoverishment in basic nutritive sub- 
stances the copper sulfate (such plants as grasses, for instance, take up 
rather considerable amounts of copper and zinc salts) acts finally also as a 
direct poison so far as cultural experiments in nutrient solutions^ have 
demonstrated. 

Masayasu Kanda- found that, in water cultures of peas, injuries 
appeared even w^ith 0.000000249 per cent, of copper sulfate. On the other 
hand, if added to soil in a concentration a million times greater, it acted as 
a stimulant. The conditions are even more favorable for plants in natural 
soil. According to Tschirch^ almost all plants possess some copper since, 
indeed, all field soils may contain traces of it. The vegetation, on soils to 
which copper is added abundantly, takes up usually but very little copper, 
so that the danger of poisoning is not imminent. This theory finds sub- 
stantiation also in the fact that in the very frequent use of copper sulfate as a 
spraying substance against parasitic diseases a constant enrichment of the 
soil takes place without any injuries being demonstrable with certainty. We 
personally believe, at any rate, that a time will come in which a constant 
addition of copper will make itself felt as a retardation to vegetation. 

The waste water containing nickel and cobalt found near nickel-rolling 
factories will act in the same way as described above. It may be mentioned 
here supplementarily that John"* in 18 19, in his book "The Feeding of 
Plants," had studied sand and water cultures to which solutions of different 
metallic salts had been added. He proved thereby that sunflowers did not 
take up copper given them in the form of insoluble copper carbonate, while 
peas and barley stored up great masses from a soil to which a solution of 
copper nitrate had been added drop by drop. 

The fact that local conditions sometimes make possible a beneficial use 
of the waste water but at other times cause injurious factors to be felt, 
prevents our consideration in more detail of the different industries. In 
this connection the poisonous peculiarity of the soil, due to its power of 
absorption, plays a principal part. Hattori^ calls especial attention to this 
in regard to copper salts. 

The injuries due to municipal irrigation with liquid sewage have been 
mentioned already in the section "Sewage Disposal Fields" (page 364). 



1 otto, R., Untersuchungen iiber das Verhalten der Pflanzenwurzeln gegen 
Kupfersalzlosung-en. Zeitschr. f. Pflanzenkrankh. 1S93, p. 322. 

2 Masayasu Kanda, Journ. College of Science. Tokyo, Vol. XIX, Art. 13. 

3 Tschirch, A., Das Kupfer vom Standpunkt der gericlitlichen Chemie, Toxi- 
kologie und Hygiene. Stuttgart 1893, Fr. Enke, S°. 138 p. 

•1 Miiller, Carl, Zur Geschichte der Physiologic und der Kupferfrage. Zeitschrift 
fiir Pflanzenkrankh. 1894, p. 142. 

5 Just's bot. Jahresber. 1902, Absch. Krankh. Ref. 277. 



CHAPTER XIX. 



INJURIOUS EFFECTS OF CULTURAL METHODS. 



A. Coating Substances. 

1. Tar. The inside of the framework of conservatories is often 
coated with tar in order to increase its resistance to great dampness. We 
are confronted with a long list of complaints that, after setting out the 
plants in the tarred greenhouses, a blackening and falling of the leaves 
takes place. I noticed the same phenomena near freshly tarred fences. The 
conditions found agree in all essentials with those described for asphalt 
fumes and are explained by the exhalations from the fresh tar coating. The 
injurious results do not appear if the tarring has taken place a few months 
before the plants are brought into the greenhouses. I found a method used 
in the vicinity of Berlin which acted as well. The boards and framework 
were treated with hard coal tar and after this had dried were coated with 
cement. 

An attempt has been made recently to keep the paths in gardens and 
public parks free from dust by means of a thin layer of tar. The process 
is much recommended^ and the experiments made in France and Italy have 
shown that even paved streets can be treated advantageously in this way. 
This process necessitates, however, the edging of the path with a strip of 
galvanized tin 8 to lO cm. high, since the injurious elements of the tar would 
otherwise attack the vegetation. This process, which despite its necessary 
annual renewal is said to be still cheaper than asphalting and less trouble- 
some than oiling, or the treatment of the streets with "Westrumit," must 
still be tested by further experiments. 

2. Refuse from Gas Works. According to a report from Mr. 
Klitzing, at Ludwigslust, where roads on sandy soil have been hardened by 
the use of such refuse, a dying back of the street trees was caused. 

3. White Lead. In a case of which I have heard, it was necessary to 
put potted plants in greenhouses a short time after these had been coated 
with white lead, and then the unpleasant discovery was made that the plants 
dropped their leaves. 



1 Das Teeren von Fuss- und Fahrweg^en in Garten und Parks. Der Handels- 
gartner, herausgeg. von Thalacker, Leipzig-Gohlis 1906. No. 50. 



757 

4- Oil Fumes. Korff ' used lead oxid as an addition to boiling Unseed 
oil in order to test experimentally the influence of oil fumes. He was led 
to make these experiments by the injuries which had occurred near a 
Unseed oil and varnish factory. Just as in the decomposition of fats by 
alkali, a mixture of fatty acid alkalies, soap, is produced, a mixture of Cor- 
responding lead salts, lead plaster, is formed similarly by the decomposing 
of fat with lead oxid. In both cases glycerine occurs as a by-product. 
When the glycerine, or fat, is heated to a high temperature fumes of akrolein 
are formed which smell like scorched fat and quickly pass over, through 
oxidation, into an akroyl acid which is recognized by its suffocating odor. 
Yellow red to brown spots are produced in the intercostal fields, or along 
the edges of the leaves according to the nature of the plant. These increase 
in size with longer action, spread and actually unite. Most of the cells of 
the leaf mesophyll, especially of the spongy parenchyma, collapse because 
of the loss of turgidity. The cell contents contract from the walls and 
the chloroplasts form greenish yellow to brown masses. Finally the struc- 
tureless cell contents and walls become brown. The elimination of tannin 
is especially noticeable in the epidermal cells, the contents of which take on 
a bluish black color with ferric chlorid. The flesh of apples and pears 
which have been exposed for 4 hours to the oil fumes has an oily rancid 
taste. 

Since akrolein, obtained by boiling glycerin, produced the same phe- 
nomena the injuries from oil fumes may in all essentials be ascribed to this 
substance. 

5. Turpentine Fumes. Molz- made experiments on the effect of 
turpentine fumes, because a case was brought him for observation in which 
the leaves of grapevines were said to have been injured by the fresh coating 
of oil in the grape house. The action of turpentine fumes on the grape 
leaves became noticeable after a half hour in the slight discoloration of the 
edges and the increased curling; after an hour, apple leaves showed a 
weakly reddish browning; after three hours, an intense dark red brown 
discoloration of the upper side. The grape leaves became an olive brown. 
At times some green areas were found within the brown surface, so that 
the leaves looked dappled. Rose leaves turned an olive brown ; pear leaves, 
a shiny, blackish gray. Molz suspects the cause to be a process of oxy- 
dation produced by "the existence of 'terpentinozone' and its action on the 
'bradoxydable' substances of the cell." 

6. Carbolineum. Like tar, CarboUneum is used, on the one hand, as 
a coating substance for the framework of greenhouses, hot beds, stakes, etc., 
in order to increase the resistance of the wood to moisture ; on the other 
hand, as a remedy for injuries to trees and a means of destroying injurious 
insects. The great difference in opinion as to its effectiveness is due in part 



1 Korff, G., tjber Einwirkung von Oldampfen auf die Pflanzen. Prakt. Bl. f. 
Pflanzenbau u. Pflanzenschutz 1906, Part 6. 

2 Bericht der Kgl. Lehranstalt flir Wein- Obst- und Gartenbau zu Geisenheim 
a. Rh. 1905. 



758 

to unsuitable manipulation and also because "carbolineum" is a general 
term ; the different kinds have different compositions and effects according 
to the factories producing them. 

In general, all that has been said of tar holds good for the use of car- 
bolineum as a coating substance. If plants are brought into rooms where 
the carbolineum coating has not dried sufficiently, they suft'er and, at times, 
show symptoms resembling those produced by asphalt fumes. Thus, for 
example, Zorn in Hofheim (Taunus) reports^ that the leaves of strawberry 
plants set out in hot beds of which only the outer side had been painted with 
carbolineum, became a peculiar brown, very shiny and curled. Under the 
subject of coating the tips of grapevine stakes, a "Chronique agricole"^ calls 
attention to the fact that even when such stakes have been painted in the 
winter and the young shoots of the grapevine have already overgrown the 
painted part in spring, unpleasant phenomena can still occur. Some berries 
on the bunches which touched the saturated spots were found with blackish 
brown spots and had a slightly tarry taste. Also the saturated parts of the 
stake were found less resistant to fungi than those treated with copper 
vitriol. It was noticed in a peach trellis which was painted in the autumn 
and exposed to the weather for the whole winter that, nevertheless, in the 
spring after every rain the youngest tips of the shoots looked as if they had 
been burned. Such occurrences are by no means uncommon. It is the 
vaporizing phenol and similar bodies which cause the injury. 

Since 1899 carbolineum has been used extensively as a remedy applied 
directly to fruit trees^. As to the results, we find some unusually laudatory 
opinions, some very harsh ones. The reason for this lies, on the one hand, 
in the difference in carrying out the experiments ; on the other, in the vary- 
ing composition of the substance which is a mixture procured in the produc- 
tion of tar from hard coal and charcoal. If the tar which is produced in 
the manufacture of gas from hard coal together with the illuminating 
gas, coke and ammonia water, is reheated in a distilling apparatus up to a 
temperature of 150 degrees C, so-called light oil is obtained; between 150 
degrees and 210 degrees C. middle oil ; between 210 degrees and 270 degrees 
C. heavy oil, and between 270 degrees and 450 degrees C. anthracene-. 

The pitch remains in the oven. Wood tar behaves in much the same 
way. In preparing carbolineum the oils above named are used since they 
are mixed in definite percentages and decomposed with kolophonium, 
asphalt, boiled linseed oil, etc. Aderhold* states that, at the present time, 
possibly 80 carbolineum factories furnish the trade with 200 to 300 varieties. 
The distillation experiments made by Scherpe in the Biological Institution 
of Agriculture and Forestry with 25 varieties proved that often the (espe- 
cially injurious) light and middle oils were absent and the heavy and 



1 Praktischer Ratgeber im Obst- and Gartenbau 1905, No. 51. 

2 Chronique agricole du canton de Vaud 1S92, No. 10. 

3 Mende, O., Zur Obstbaumpfleg-e. Gartenflora, 1906. No. 1. 

4 Aderhold, R., Karbolineum als Baumschutzmittel. Deutsche Obstbauzeitun^ 
(Ulmer-Stuttg-art) 1906, Part 22. 



759 

anthracene oils alone were present, while in other varieties the opposite was 
found to be true. Accordingly, the results in treating wounds were very 
different. While normal overgrowth occurred with some, with others there 
was a very visible increase in the size of the wounds due to the dying back 
of their edges. 

But, aside from this, the carbolineum as a means of closing wounds, 
even in the viscid varieties abounding in pitch and asphalt, does not stand 
comparison with plain hard coal tar, for Aderhold has observed that a few 
weeks after the painting, fungus species had already appeared on the car- 
bolineum surfaces. Since the painted surface may also crack, under the 
influence of the atmospharilia, such fungi have a good opportunity of pene- 
trating into the wood. 

In regard to the very fluid kinds of carbolineum, that is, those rich in 
light and middle oils, which are warmly recommended for coating trees 
attacked by red aphis and scale^, the promptness of their action in killing 
insects is unmistakable, but its protection is not permanent. The recoloni- 
zation of the painted wounds by red aphis has been repeatedly confirmed. 
To this should be added, however, the often observed injury to the buds 
which cannot be avoided in painting or spraying the trees and which is to 
be ascribed especially to the vaporization and direct action of the light oils. 
Therefore, the substances should be diluted. It is advisable to use the 
commercial carbolineum varieties which are soluble in water and to add 
them to lime water up to about 20 per cent.- ; even an addition of 10 per 
cent, acts favorably^. 

An action directly favoring growth is said to have been observed in 
trunks thus coated*, and also the increase of the chlorophyll content of the 
painted bark has been microscopically determined in Brunswick with the 
use of a definite brand^. We believe that this result is due to the fact that 
in coating smooth barked trunks tears are frequently produced in the bark 
which must be overgrown subsequently. An increased bark activity in the 
overgrowth walls has also been proved in common scarification. 

The use of this substance as a coating for trees is advisable only during 
the dormant period and in fact with some tested brand. "Schacht's fruit 
tree Carbolineum" (containing 20 to 30 per cent.) has been repeatedly 
recommended". We would never advise spraying in summer. As a means 
of closing wounds we would prefer coal tar because not only Aderhold's 
discoveries, but also experiments made by Schweinbez'' in Hohenheim, and 
our own have shown no advantage in the use of carbolineum. Its recom- 



1 Baumann, R. Geisenhelm. Prakt. Ratgeber 1905, p. 459. 

2 Praktischer Ratg-eber im Obst- und Gartenbau 1906, No. 49. 

3 Praktische Blatter fiir Pflanzenbau und Pflanzenschutz, herausg. v. Hiltner. 
1906, November. 

4 Gartenfloi-a 1906, No. 3. 

5 Graef, tjber Karbolineumversuche im Jahre 1906, Prakt. Blatter f. Pflanzen- 
bau und Pflanzenschutz, 1907, Part 3. 

6 StefCen in Prakt. Ratgeber 1906, p. 23. 

7 Vom Karbolineum. Gartenflora 1906, p. 22. 



76o 

mendation as a remedy for chronic gummy exudations is based at least upon 
self-delusion if not the exigencies of advertising. 

Schweinbez holds the same opinion of the related substances "Tuv", 
"Dendrin", "Baumschutz", "Neptun". 

7. Lyzol. Formerly lysol had its enthusiastic adherents and doubters 
just as carbolineum has them now. The Lysolum purum of Scholke and 
Mayr in Hamburg, introduced into trade about the end of the 8o's of the 
last century, is a transparent, brown, syrup-like fluid which remains dissolved 
and perfectly clear in pure water, and has been extensively used as a means 
of disinfection. In introducing it, it was said that, according to experi- 
ments, 3g. of lysol to a litre of liquid was enough "to destroy, in 15 to 20 
minutes, bacteria in all their developmental forms, if suspended in liquids." 
We are concerned here with a solution of tar oils in neutral soap and, 
indeed, with the light tar oils (cresol), for they volatilize almost entirely 
between 187 and 200 degrees^. In contrast to other commercial products, 
like creoline, cresoline, Little's Soluble Phenyle, which, as solutions of resin 
or fatty soap in tar oil only form emulsions with water and usually give off 
carburetted hydrogen oil (Ethylene), when diluted, lysol has the advantage, 
at any rate, of complete solubility in water, but shares with the above 
preparations an injurious effect on the tissues of plants. It was used in 
horticulture mostly as a spraying substance for leaf lice, thrip, black fly, and 
other injurious insects. Otto's- cultural experiments, made soon after the 
introduction of the substance, showed that 0.5 per cent, lysol solution, the 
one commonly used for disinfection, proves to be a severe poison for plants 
if added tO' the soil, even if it does not come directly in contact with the 
seeds or seedlings. With direct action, even in a much more diluted form, 
it attacks uncommonly sharply the roots of water cultures. It was used in 
a 0.25 to 0.5 per cent, solution as a protection against leaf lice. In this, 
however, it kills only some of the leaf lice, the majority of which die only 
with a 2 per cent, solution ; the plants were then so blackened and injured 
that they could not be considered capable of further life. 

8. Carbolic Acid, Amylocarbol, and Sapocarhol. The amylocarbol is 
a mixture of soft soap, fusel oil, and pure carbolic acid. Sapocarbol is 
saponified carbolic acid. 

All substances containing carbolic acid are dangerous and usually 
directly fatal for plants. In Fleischer's experiments^ with the above prepa- 
rations, the sapocarbol in one per cent, solution was effective for leaf lice 
without any injury to the leaves from the spraying, with a few exceptions. 
In dilutions which completely kill the leaf lice, Pino sol and Creolin act injuri- 
ously since both can only be emulsified in water. The Antinonnin, the 



1 Zeitschr. f. Pflanzenkrankh. 1S91, p. 185. 

2 Otto, R., tJber den schadlichen Einfluss von wasserigen, im Boden beflnd- 
lichen Lysollosung-en usw. Vorl. Mitt. Zeitschr. f. Pflanzenkrankh. 1892, p. 70fC. 

3 Fleischer, E., Die Wasch.- und Spritzmittel zur Bekampfung der Blattlause, 
Blutlause u. ahnliclier Schadlings usw. Zeitsch. f. Pflanzenlvrankh. 1891, p. 325. 



76i 

potassium salt of Orthodinitro-Cresol is more injurious to plants, according 
to Frank's experiments^, than to leaf lice and other animal parasites. 

9. Refuse from Lactic Acid Factories. To those injuries we will add 
a case which we owe to a report from Mr. Klitzing of Ludwigslust. He 
noticed that the refuse from a factory which produced lactic acid from maize 
and potatoes, for the treatment of leather, caused the death of plants. 

10. Calcium arsenite. The arsenic solutions which are being accepted 
more and more as a means for combating insects are used as a rule in the 
form of Schweinfurter green, or calcium arsenite. Injuries to the leaves 
have been observed in aqueous solutions as also in lime water or Bordeaux 
mixtures, or sodium arsenite calcium solutions. In general we would refer 
to the special books on the subject". 

11. Hydrocyanic -acid. Fumigation with hydrocyanic acid has recently 
been accepted as a modern method of combating animal parasites in plants 
and has been developed especially in America. It may be said in general, in 
opposition to individual complaints of injuries to plants, that these should 
not prevent the use of this substance'. Townsend confirmed, for dry seeds, 
that the germinating capacity does not suffer if the action of the hydrocyanic 
gas is not continued longer than is necessary for killing animal life. A 
longer treatment, however, causes considerable injury. Moist seeds suffer 
more quickly and lose their power to germinate. 

12. Copper solutions. These come under consideration here only in 
so far as their injuriousness is concerned. Their usefulness as fungicides, 
which will be considered in the second volume of this book, depends, in our 
opinion, chiefly upon the fact that the fungi give out ferments which dissolve 
the copper salts dried on the plant parts and thus poison themselves. 
Bordeaux mixture which, without doubt, is of great importance as a means 
for fighting fungi, may primarily favor growth, as its enthusiastic advocates 
would like to prove, but it cannot be acknowledged as a promotor of growth. 

Opinions as to whether the copper can penetrate through a normal 
cuticle in all plants are not unanimous. According to Bouygues* this is not 
the case. Rumm° also could not prove the existence of copper in the tissue 
of sprayed leaves and believes that the favorable action can be traced only 
to the chemico-tactic stimulus. The electric currents, resulting from it, are 
said to cause the favorable effect in the leaf tissue. The question whether 
copper can react on the interior of any part of a plant and how, cannot be 
decided universally but must be taken into consideration case by case. Old 
cuticule, provided with a thick wax coating, will possibly not be attacked 



1 Krankheiten der Pflanzen 1895, Vol. I, p. 329. 

2 HoUrung-, M., Jahresbericht auf dem Gebiete der Pflanzenkrankh. Berlin, Paul 
Parey. Published since 1898. HoUrung-, M., Handbuch der chemischen Mittel gegen 
Pflanzenkrankheiten. Berlin 1898. Paul Parey. 

3 Townsend, W. O., tJber die Wirkung- gasformig-er Blausaure usw. Bot. Gaz. 
XXXI; cit. Bot. Jahresber. 1902, I, p. 354. 

4 BouygTies, H., La cuticule et les sels de cuivre I; cit. Centralbl. f. Bakt. usw. 
1905, N. 24. 

5 Rumm, C, Zur Frage nach der Wirkung der Kupferkalksalze usw. Ber. d. 
Deutsch. Bot. Ges. 1893, p. 445. 



762 

while a young leaf can suffer. In older leaves, however, injuries may also 
occur in one case and not in another; the cuticle covering may be broken by 
atmospheric action (late frost) and the copper solution may remain for some 
time in these tears. Finally, the specific sensitiveness of the plant variety is 
decisive, as will be shown in later examples. 

The first doubt as to the peculiarity of copper mixtures for favoring 
growth arose from the results of some spraying experiments made in 1891^ 
An arrestment in the development of potato plants could be proved as com- 
pared with unsprayed plants which remained healthy. The considerable 
amounts of starch and chlorophyll contained in leaves treated with copper 
which are considered as an indication of favoring growth were traced by 
Schander to the effect of the shade caused by the calcium copper coating-. 
Ewert confirms the effect of shading but calls attention to the fact that this 
may not be the only arresting factors Through the effect of the copper sub- 
stances, especially Bordeaux mixture, stoppages occur in the transference of 
the assimilates. The considerable amounts of starch and protein, here 
observed, are not the results of increased assimilation which, as has been 
proved, is repressed together with transpiration and respiration, but is the 
action of arrested transpiration. This point of view which we represent 
presupposes, at any rate, that copper actually enters the plant and this theory 
is substantiated by the fact that scientists who do not assume a penetration 
of the copper still find copper reactions in a number of their experiments 
(Frank and Kruger). Besides this, Ewert has also proved the presence of 
copper in plants sprayed with Bordeaux mixture. Later we will quote notes 
from Schander's work as to the way in which the copper is taken up. 

In my opinion, the copper, entering through wounds, or through the 
epidermis of plants treated with copper mixtures, is combined at once with 
the proteins of the protoplasm and thereby reduces cell-life. Since spraying 
does not represent a complete wetting of all the leaf surface, certain areas 
remain healthy, between injured ones, and these must show an increased 
growth activity. This makes itself evident at times with an abundant 
supply of light and moisture, in the formation of intumescences. I described 
the first case of this kind in potatoes*. Later v. Schrenk"' observed intu- 
mescences on cabbage plants as a result of their treatment with copper- 
ammonium-carbonate, copper chlorid, copper acetate, copper nitrate and 
copper sulfate. Very recently Muth'' has observed a very strong formation 
of intumescences in grape leaves after a treatment with copper. 



1 Sorauer, P., Einige Beobachtung-en bei der Anwendung von Kupfermitteln 
g-egen die Kartoffelkrankheit. Zeitschr. f. Pflanzenkrankh. 1893, p. 32. 

^ Schander, E., tjber die pliysiologische Wirkung der Kupfervitriolkalkbruhe. 
Inaug.- Diss. Berlin 1904 und Landwirtsch. Jahi'biicher 1904, Parts 4 and 5. 

3 Ewert, Der wechselseitige Einfluss des Lichtes und der Kupferkallcbriihen 
auf den Stoffwechsel der Pflanze. Landwirtsch. Jahrbiicher 1905, p. 233. 

4 Zeitschr. f. Pflanzenkrankh. 1893, p. 122. 

5 Schrenk, H. v.. Intumescences formed as a result of chemical stimulation. 
Sixteenth annual report Missouri Botanical Garden. Mxiy, 1905. Special reprint. 

6 Muth, Franz, tJber d. Beschadigung d. Rebenblattern durch Kupferspritzmittel. 
Mittel. d. Deutsch. Weihbauvereins I. Jahrg. No. 1, p. 9. 



7^3 



Such effects may be produced if the tissue is partially poisoned but does 
not actually die. They may also occur, however, when death actually takes 
place in which case the dead tissue areas in many plants fall out of the leaf, 
causing perforation. Such cases have recently been described by Schander' . 
In connection with this, it is mentioned that Fuschia and Oenothera secrete 
acids which dissolve small amounts of copper hydroxid. Alkaline secretions 
have also been found (Phaseolus multiflorus) , or the copper is dissolved not 
by secretions of the leaf but simply by the atmospharillia, especially with 
continued wet weather. 

Ruhland- declares, on the other hand, that the assumption of a dissolv- 
ing of the copper by leaf secretions has no justification, and that this can be 
ascribed only to the atmospharillia. 

Reports as to the injury to foliage from spraying with copper have 
appeared as the process has been more generally used. In 1891 it was 

observed in fighting Peach rot that, 

after using Bordeaux mixture, not 

only the leaves and blossoms fell, 

but the young wood also was in- 

jured-'. The Amygdalaceae and 

especially peaches have been found 

to be especially sensitive. Bain* 

showed in his experiments with 

apple, grape and peach leaves that 

this is connected with the specific 

sensitiveness of the protoplasm. He 

says that the peach leaf is able to 

dissolve copper oxid by a substance 

secreted on its upper surface. 

Young leaves suffer most. The in- 
jured part of the leaf is then cut off 

by a cork layer and thrown off 

(Shot disease, which Aderhold^^' has also described for the cherry). Severely 

diseased peach leaves fall but the apple leaf, as well as the grape, possesses 

the ability to continue assimilation by means of the remaining lamina. 

According to Hedrick's" more recent studies, peaches, apricots, and 

Japanese plums are the most sensitive fruit trees, while the common plum is 

not affected more severely than the pear, apple or quince. The different 

varieties behave differently. The most highly cultivated examples, with the 

1 Lioc. cit. 

2 Ruhland, W., Zur Kenntnis der Wirkunj? des unlosliclien basischen Kupfers 
auf Pflanzen usw. Arbeiten d. Biol. Abt. f. Forst.- u. Landwirtsch. beim Kaiser 
Gesundheitsamt Vol. IV, 1904, Part 2. 

3 Report of the Secretary of Agric. for 1891, Washington 1892, p. 364. 

4 Bain, S. M., The action of copper on leaves, etc. Ag-ric. Exp. Stat, of the 
University of Tennessee, 1902, Vol. XV. 

fi Aderhold, R., tJber Clasterosporium carpophilum usw. Arb. d. Biolog- Abt d 
Kais. Gesundheitsamtes, 1902, Part .5. 

6 Hedrick, U. P., Bordeaux injury. New York, Agric. Exp. Stat. Geneva. Bull. 
No. 287, 1907. 




Fif 



169. An apple with brown spots and 
cracks. (After Hedrick.) 



764 

most watery leaves, suffer most. Atmospheric conditions have great influ- 
ence, and on them depends the more delicate, or coarser development of the 
leaves and especially of their cuticule. The year 1905 furnished the best 
proof in New York State. Its warm, misty, spring weather left the foliage 
very tender. Many apple growers declared that there was greater injury in 
that year than benefit from spraying with Bordeaux mixture. Hedrick 
cites examples in which spraying was unusually injurious when the following 
weather continued moist, while 8 days later after dry weather had set in the 
spraying did not have any bad effects. 




Fig. 170. 



Young- apples with one-sided malformation, after spraying with Bordeaux 
mixture. (After Hedrick.) 




Pig. 171. Cross-section through the bark of a Baldwin apple injured by spraying 
with Bordeaux mixture. (After Hedrick.) 



We have borrowed from the above mentioned author some illustrations 
of fruit and leaves which have been injured by spraying. The injury at 
first appears on the fruit in the form of small brown specks which spread to 
extensive rust markings (Fig. 169). If these injuries to the upper surface 
occur during the period of swelling, the growth of the fruit may become 
irregular (Fig. 170), or gapping cracks may be produced in young apples. 
Fruit thus injured becomes mealy and easily decays. 

Microscopic investigation of the brown spots shows that the cuticle 
covering with its wax coating is destroyed (Fig. 171). The walls of the 
adjacent epidermal cells and the exposed flesh become greatly thickened and 



765 

give a cork-like appearance. They cannot respond any longer to the swelling 
of the fruit, which, therefore, cracks. The wound cork formed in the 
cracks, together with the tissue killed by the Bordeaux mixture, then causes 
the peculiar "rust figures" shown in Fig. 169. The amount of injury 
increases with the tenderness of the skin, which shows the initial stages of 
browning, as a rule, around a hair or a stoma. With the increasing age of 
the fruit, the hairs are thrown off normally and lenticels are produced instead 
of stomata. In this the wax 
coating is thickened and the 
fruit becomes immune to the 
poisonous copper. Brown spots 
may be produced also on the 
leaves which at times repture 
(Fig. 172). Naturally the 
blossoms suffer most severely. 
It can be assumed with cer- 
tainty that in these blossoms 
the copper unites with the cell 
contents. Hedrick's remark 
that a considerable addition of 
lime scarcely decreases the 
injury is worthy of consider- 
ation in regard to the prepa- 
ration of the Bordeaux mix- 
ture. This is treated more 
thoroughly in the second vol- 
ume of this book (page 521). 
All that is true of calcium 
copper mixtures holds good to 
a higher degree in the Asurine 
in which ammonia is used to 
neutralize the copper vitriol. 
Pure deep blue solutions are 
produced, according to the 
amounts of ammonia used, 
such as "Bouille Celeste" and 
the "Asurine Siegwart," or 

especially with greater dilution basic copper compounds remain as a precipi- 
tate, as is found in the "Crystal- Asurine Myl'ius." The more ammonia used, 
the greater is the danger of burning the leaves^ 

Anaesthetica. 

In considering the so-called "forcing with ether," that is to say the 

process of exposing the plants to ether vapor in order to hasten their growth, 

1 Kuliscli, p., tjlier die Verwendvmg' der "Azurine" zur Bekampfung' dor 
Peronospora. Landwirtsch. Z. f. Elsass- Lothringen 1907, No. 26. 




Fig. 172. Apple leaf with dead spots and holes 

in the tissue, after spraying with Bordeaux 

mixture. (After Hedricli.) 



766 

we must take up also the subject of anaesthetica. The favorable results 
which can be obtained, especially in the early forcing of lilacs, by a proper 
use of this method are certain beyond doubt ; but with an incorrect use dis- 
advantageous results become noticeable. The action of ether, chrom-ether 
chloroform, nitrous oxid, morphine, cocaine, etc., as proved by repeated 
experiments, consists in retarding the complete development of protoplasmic 
activity. If, in this, the protoplasm undergoes a continued injury to its 
physical or chemical structure, death follows ; otherwise, the plant gradually 
returns to the normal activity. \ Naturally the effect depends upon the con- 
dition of the protoplasm. Thus, Coupin- has proved that even an atmos- 
phere saturated with chloroform and ether can exert no influence on the 
protoplasm of seeds in a dormant stage. If, however, their life activity has 
been aroused by moistening very small amounts (.00037) are enough to 
cause injury. Yet the figures given here should not be considered as a 
standard, for aside from the individuahty of the species even plants of the 
same species can develop a different power of resistance by self adjustment. 
Thus, for example, Townsend^ states that spores of Mucor and Penicillium 
ripened under a strong ether atmosphere germinated and produced spores 
just as quickly as when they had germinated in an atmosphere free from 
ether. The same observer mentioned that here and in other poisons very 
weak doses act as a stimulus and shorten the period of germination, while 
stronger doses are injurious. 

The observations of Markowine* give an insight into the kind of action. 
He draws the conclusion from his experiments that, in the long continued 
action of anaesthetizing vapors, respiration becomes considerably increased. 
He found that, under the influence of alcohol vapor, the respiration of 
etiolated plants was increased more than one and a half times; ether acted 
still more strongly. 

We may assume here a specific response to stimulation, Behrens^ also 
holds this theory. He would like also to consider as a response to stimula- 
tion the hastened germination of seeds after mechanical injury which Hiltner 
ascribes to the f aciUtated absorption of water. Behrens bases his theory on ex- 
periments with injured seeds in which the wounded places were covered at 
once with colophoneum wax. Although the absorption of water by these grains 
did not seem increased as compared with normal grains, there appeared, never- 
theless, an appreciable increase of growth. Experiments with fihng and 
other intentional injuries to hard shelled seeds proved, however, that even 
the mechanical facilitation of the entrance of water favors germination. 

1 Kaufmann, C, tJber die Einwirkung- der Anaesthetica auf das Protoplasma 
und dessen biologisch-physiolog-ische Eigenschaften; cit. Just's Jaliresber. 1900, II, 
p. 301. 

2 Coupin, H., Action des vapeurs anesthesiques sur la vitalite des graines 
s6ches et des graines humides; cit. Just's Jaliresber. 1900, II, p. 301. 

3 Townsend, C. O., Tlie effect of ether upon the gei-mination of seeds and 
spores; cit. Just's Jahresber. 1899, II, p. 142. 

4 Markowine, N., Recherches sur I'influence des anesthesiques sur la respiration 
des plantes; cit. Just's Jahresber. 1899, II, p. 143. 

5 Behrens, Bericht d. Grossherzogl. Badischen Landwirtsch. Versuchsanstalt 
Augustenberg f. d. Jahr. 1906. 



7^^7 
Injuries Due to Fertilizers. 

I : Chili saltpetre. Unfavorable secondary and subsequent effects 
have, often been observed with the use of Chili saltpetre. The cause lies in 
part in the presence of potassium-hyperchlorate. Numerous cultural experi- 
ments have proved that grain is especially sensitive and shows striking 
injuries with 2 per cent, hyperchlorate, while alfalfa, peas and mustard 
could endure this concentration. In rye, a deformation of the plant was 
observed when grown as a late crop^ Vegetables, requiring hoeing, and 
sugar beets were not injured by 2 per cent, hyperchlorate to 200 to 500 kg. 
saltpetre per hectar-. Jungner and Gerlach^ describe the formal changes in 
wheat and rye seedlings as follows : The primordial leaf remains for some 
time partially rolled and encloses the secondary leaf so firmly that it loosens 
its tip only with difficulty and consequently forms a loop, or knot, in which 
it is folded crosswise and rolled about its own axis ; it finally may even tear. 
At the same time a yellowing of the leaf tip takes place and a considerable 
reduction in the elongation of the whole plant. Retardation of germination 
will occur, in fact, according to the amount of hyperchlorate present. This 
has not been observed with weak doses. The forming of loops by leaves 
because of the retention of their tips in, the sheath of the next older leaf 
seems to be a marked characterization of grain when poisoned with hyper- 
chlorate. It is, however, not limited to grain, since similar phenomena occur 
in Xylene hus devastatrix^. 

Dafert and Halla^ describe a case of the appearance of free iodine in 
Chili saltpetre which thus gave the odor of iodoform. The saltpetre con- 
tained 0.31 per cent. KCLO4 and 0.04 per cent. KIO.. In such cases, how- 
ever, the danger is slight in general agriculture, since it is only necessary to 
expose the sacks of Chili saltpetre to the air in order to evaporate the iodine. 
Voelker*', among others, has showed that the iodids of manganese, potassium, 
sodium and lithium act injuriously while the oxids are proved to be favorable. 
In connection with his earlier experiments by which he proved the injurious- 
ness of larger amounts of sodium iodid and bromid and of lithium chlorid, 
while, on the otlier hand, an advance in germination was found when the 
seeds v/ere moistened with more dilute solutions, Maze^ concludes that the 



1 Ullmann, Martin, In welchem Grade ist Kaliumperchlorat ein Pflanzeng-iff 
Die Regelung- des Verkehrs mil Chilisalpeter. Meffe 1901. Cit. Centralbl. f. Agril<ul- 
turchemio 1903, Part 7. 

2^ Stoldasa, Beitrag-e zur Kenntnis des schadlichen Einflusses des Chilisalpeters 
auf die Vegetation. Z. f. d. landwirtsch. Versuchswesen in Osterreich 1900, p. 35. 

3 Jnngner und Gerlach, Versuclie mit Kaliumperchlorat. Jaliresber. d. landw. 
Versuclisstation in Jersitz bei Posen 1897-9S, p. 29. 

4 Kriiger, Fr. u. Berju, G. Ein Beitrag zur Giftwirlcung des Chilisalpeters. 
Centralbl. f. Bakt. II, 1898, Vol. IV. p. 674. 

5 Dafert, F. W., u. Halla, Ad., tjber das Auftreten von freiem Jod im Chilisal- 
peter. Z. f. d. landw. Versuchswesen in Osterreich 1901. 

6 Voelker, A., iiber den Einfluss von Mangansalzen sowie von Jodiden und 
Oxyden von Mangan, Kali, Natrium und Lithium auf Gerste und Weizen. Journ. 
Royal. Agric. Soc. of England, Vol. 64 and 65; cit. Centralbl. f. Agrikulturchemie 
1905, p. 715. 

7 Maze, Einfluss der in den Pflanzen in geringer Menge enthaltenen Mineral- 
stoffe auf das Pflanzenwachstum. Biedermann's Centralbl. f. Agrikulturchemie 
1902, p. 686. 



768 

cell needs stimulation by such salts for the complete development of its 
functioning. Aso^ has made similar discoveries as to the injuries due to 
stronger concentrations of sodium fluorid and the favoring of growth by 
very weak concentrations. Suzuki- has also found this to be true of 
potassium iodid. Similar discoveries have often been observed by others. 
Miani^ also reports the favorable action of copper solutions. 

2 : Superphosphate. We should briefly consider the breaking down of 
phosphoric acid in superphosphate and Thomas meal in many soils which are 
rich in calcium and ferric oxid. In sour, marsh soil and sour meadow soil, 
rich in humus, retention of the phosphoric acid in a soluble form predomi- 
nates since water, carbon dioxid, humic acid and some salts act as solvents. 
In sandy soil containing humus but not acid the process of solution is approx- 
imately held in equilibruim with the process of transforming the dissolved 
phosphoric acid into less soluble forms but in loamy soils, containing calcium 
and iron, the process of decomposition preponderates, that is, the process of 
transforming the soluble phosphoric acid into phosphates which are dissolved 
with difficulty. Under such circumstances the use of Thomas meal in the 
spring would not be advisable. 

3 : Gas phosphate. Rhodanammonium is found in different amounts 
in the refuse of gas factories. This has attained a heightened agricultural 
significance since a fertilizer, containing nitrogen, has been produced by the 
purification of illuminating gas with superphosphate, and has been introduced 
in trade as "gas phosphate." The acid phosphate has taken up the ammonia 
from the stream of illuminating gas but at the same time has retained the 
Rhodanammonium. Because of the repeatedly proven poisonous quality of 
this compound the purification of the fertilizer has been attempted by wash- 
ing the gas phosphate with a concentrated solution of ammonium sulfate 
in which the Rhodanammonium compounds are easily soluble. The amount 
of Rhodan compounds contained could be reduced thereby to 0.9 per cent, 
and, consequently, the direct use of this fertilizer has been recommended. 
It is, in fact, distinguished by its large content of phosphoric acid and 
nitrogen. 

The experimental results are contradictory in that favorable effects have 
been observed on sandy soil and unfavorable effects on loamy soils. This 
brought about the supposition that, in sandy soils, a more rapid decompo- 
sition of the Rhodanammonium into ammonia, nitric acid and sulfuric acid 
occurs whereby the poisonous effect is repressed. This hypothesis is con- 
firmed by other experiments which demonstrate that in using the fertilizer 
some weeks before seeding, no injuries appear, while severe losses take place 
when it is used simultaneously with seeding. The same result was found 
in using dust from a blast furnace containing i per cent. Rhodanammonium. 



1 Aso, Bull. Coll. Agric. Tokyo; cit. Bot. Jahreslier. 1902, p. 353. 
- Suzuki, S. Ibid. 

^ Miana, D., tjber Einwirkung von Kupfersulfat auf das Wachstum lebender 
Pflanzenzellen. Ber. d. Deutsch. Bot. Ges. 1901, Part 7. 



769 

The recent experiments of Haselhoff and GosseF leave no doubt as to 
the poisonous effect of Rhodanammonium, the decomposition of which even 
in sandy soil does not take place so easily as earlier examples seemed to 
prove. Even a very small amount, such as 0.0025 per cent., produces a con- 
siderable delay in germination and since the purified gas phosphate still 
contains 0.76 per cent. Rhodanammonium the above named scientists could 
not recommend it at all as a fertilizer, even with the difficult solubility of 
phosphoric acid. 

4: Ammonium sulfate. In connection with this, a case of injury 
due to ammonium sulfate should be mentioned here, which was previously 
unknown. A car full of plants (Azaleas), when opened, showed that the 
leaves had been partly blackened as if from ammonia fumes. Subsequent 
investigations showed that the car had been used previously for the trans- 
portation of ammonia sulfate. Experiments made immediately proved that 
free ammonia developed in the presence of calcium. In the same way, fresh 
ammonium sulfate which has not been sufficiently dried and neutralized 
can develop ammonia and as in the case described in the section on am- 
monium fumes this can adhere to the walls and subsequently act injuriously. 

5 : Calcium nitrid. This recent product of our fertilizer industry still 
gives rise to repeated complaints. Calcium carhid used primarily in the pro- 
duction of the very bright illuminating gas, acetylene, and obtained from the 
interaction of lime and carbon in an electric oven is exposed in hermetically 
sealed iron mufflers to the action of nitrogen with intense heat and then 
furnishes the calcium nitrid as an unpurified calcium cyanamid with possibly 
20 to 24 per cent, nitrogen. This calcium nitrogen, or calcium cyanamid, has 
the peculiarity of giving off all its nitrogen in the form of ammonia when 
heated with water under pressure. By passing the ammonia through sulfuric 
acid it is possible to produce the valuable fertilizer, ammonium sulfate. 
The "calcium nitrid" (CaCN.) contains about 20 to 21 per cent, nitrogen; 
40 to 42 per cent, calcium and 17 to 18 per cent, carbon, besides impurities of 
silicic acid, clay, traces of phosphoric acid, etc. By removing the calcium, 
there are produced Cyanamid (CN,NH.,) and the homologous Dicyandiamid 
[CN.CNH,)^. 

The calcium, present in the calcium nitrogen, which acts as a strong 
alkali, is partly free and partly combined in the form of calcium cyanamid. 
For this reason it should not be brought into contact with supersulfat 
because the phosphoric acid would then be made insoluble. The rules for its 
use are approximately as follows :- — The quantity used per hektar according 
to the constitution of the field, is 150 to 300 kg. corresponding to 30 to 60 kg. 
nitrogen. To avoid the loss in dust the calcium nitrid is mixed with twice 
the amount of dry earth. This should be spread i to 2 weeks before the 

1 Haselfhoff, E., u. Gossel, P. Versuche iiber die Schadlichkeit des Rhodanam- 
uioniums fur das Pflanzenwachstum. Zeitschr. f. Pflanzenkrankh. 1904, p 1 Bibli- 
ography here given. 

2 Brahm, Der Kalk.stickytoff und seine Verwendung- in Gartenbau und Land- 
wirtschaft. Gartenflora, Berlin, 1906, Part 10. 



770 • 

sowing of the seed and the fertihzer must be covered at least 3 to 5 inches 
so that tlie soil can take up the ammonia freed by the action of the soil 
moisture and thus be nitrified. 

The production of the ammonia from the calcium nitrate takes place by 
means of bacteria^. 

The fertilizing experiment, carried out in vegetating vats, has shown 
the possibility of obtaining the same fertilizing action with calcium nitrid as 
with saltpetre nitrid and ammonia nitrid. In all field experiments, made as 
yet, the calcium nitrid has developed about 74 per cent, of the action of the 
saltpetre nitrid"-. 

The agriculturalist will cause great injury if he sow^s his seed soon after 
scattering the calcium nitrid. Usually only those grain seeds will then 
sprout which lay on the ridges of the furrows. If the first shock is over- 
come, the abundant supply of ammonia manifests itself in the especially dark 
green of the plants. The injur}^ consists of a drying of the leaf parenchyma 
and a poor root development^. The calcium nitrid may not be used as a 
top dressing any more than as a direct fertilization before seeding. This 
substance acts unfavorably on certain soils even if it is hoed under according 
to rule. Remy* found the most favorable action on clayey soils. On sandy 
soil, however, action was considerably slower and the directly injurious effect 
on germination much more persistent. Only three months after fertilization 
did he find that the injurious efi^ect in the sandy soils had disappeared. All 
soils, tending to the formation of acids, retard the normal formation of 
ammonia. Tacke has proved that, on acid soils, the transformation into 
ammonia is so hindered that fertilization of marshes with calcium nitrid 
must be omitted there. On the other hand, when a great deal of calcium is 
present in the soil, the ammonia formation can take place so rapidly that 
extensive losses arise from the vaporization of the ammonia. On high moor 
soils poisonous action is found which, according to Gerlach, may be traced 
back to the fact that, with the decomposition of the calcium cyanamid and 
the deposition of the calcium, considerable amounts of the poisonous dicyana- 
mid are produced within a few days. 

The conversion of the ammonia into ammonium sulfate, which thus 
overcomes these disadvantages, is useless for agriculture, since the cost of 
the nitrogen would thus become too great. 

A still newer fertilizer is associated with this "calcium nitrid," "the 
nitrogen calcium" which is free from cyanamid compounds and contains 22 
per cent, nitrogen ; 19 per cent, carbon ; 6 per cent, combined chlorin ; and 45 
per cent, calcium. Bottcher's^ experiments have shown that with this, how- 



1 Lohnis, F., tJber die Zersetzung' des Kalkstick-stofCs. Centralbl. f. Bakt. 1905, 
II, Vol. XIV, p. 87. Behrens, J., Versuche mit KalkstickstofC. Bericht der Gross- 
herzog-1. Bad. landw. Versuchsanstalt Aiigustenberg- 1904, Karlsruhe 1905, p. 36. 

- Gerlach u. Wagner, P., Gewinnung 11. Landwirtschaftliche Verwendung des 
Salpeterstickstoffs. Verhandl. d. Winterversammlung- 1904 d. Deutsch. Landwirtsch. 
Ges. Jahrb. d. D. L. G. Vol. 19, p. 33-39. 

3 Perotti, R., tJber die Verwendung des Calciumcyanamids zur Diingung. Staz. 
sper. agrar. Ital. 1904, Vol. XXXVII; cit. Centralbl. f. Agrikulturchemie 1905, p. 814. 

4 Blatter f. Zuckerriibenbau, 31 May, 1906. 

5 Deutsche landw. Presse 1906, No. 34. 



771 

ever, the same precautionary measures are necessary as with calcium nitrid. 
It may not be used immediately before seeding, nor as a top dressing, because 
it is then injurious'. 

In regard to the Ammonia nitrid, we should not forget to call atten- 
tion to the fact that it may also become injurious under conditions in which 
the nitrifying bacteria do not act sufficiently. For heavy soils, which contain 
more water and, therefore, dissolve the ammonia more abundantly there is 
no danger, but in sandy soils the retarded solubility may lead to direct 
phenomena of corrosion-. 



1 Blatter, f. Zuckerrtibenbau 1906, No. 10. 

- Maze, Unteisuchungen iiber die Einwirkungen des Salpcterstickstoffs und 
des Ammoniakstickstoffs auf die Entwicldung- des Mais. Annal. agron. t. 26; cit. 
Centralbl. f. Agrikulturchemie 1901, p. 588. 



SECTION V. 

WOUNDS. 

CHAPTER XX. 



WOUNDS TO THE AXIAL ORGANS. 



General Discussion. 

However much accidental or intentional injuries to the tree trunk may 
differ, nevertheless, the process of healing always agrees in the essential 
points. 

We find, in all cases in which the injury to the trunk and branches is so 
extensive, that the wood body composes part of the wound surface and that 
both the cambium lying between wood and bark which with undisturbed 
development makes possible the growth in thickness of the trunk as well as 
the young tissue elements directly formed from the cambium (which in the 
following will be included under the term "Cambium"), take over the heal- 
ing of the wound surface of the mature part of the trunk. In herbaceous 
stems, or the still herbaceous developmental stages of woody trunks and 
branches other tissue forms can participate in healing the wounds as will be 
show^n later in discussing individual cases under this head. 

The structures of the forms developed from the cambium in the healing 
of wounds may, how-ever, vary greatly from that of the normal wood ring. 
The reason for this difference in structure of wound zn'ood should be sought 
in the fact that pressure conditions under which the tissue, serving for 
healing the wound, is produced, are very different from those existing during 
the formation of the normal wood body. 

Supported by the investigations of G. Kraus, it should be recalled first 
of all that each trunk and branch has considerable internal tension, due to 
the difference in growth of its individual tissue forms which are connected 
with one another. The experiments on tissue tension begun by Hofmeister^, 
extended by Sachs-, and especially fully carried out by Kraus^, have proved 

1 Hofmeister, tJber die Beug-ung- saftreicher Pflanzenteile durch Erschiitterung. 
Ber. d. Kgl. Sachs. Ges. d. Wissensch. 1S59, p. 194. 

- Sachs, Experimentalphysiolog-ie, p. 465-514. 

3 Kraus, Gregor, Die Gewebespannung des Stammes und ihre Folgeii. Botan. 
Zeit. 1867, No. 14. ff. 



773 

that the growth in length of each branch of our trees is regulated by two 
factors. 

The central tissue of the shoots, especially the pith, is tke elongating 
factor^ the tissue which forces the shoot into the air. Its very considerable 
striving to grow longer and to carry the surrounding tissue with it into the 
air which becomes evident in an isolation from other tissues is modified and 
retarded by the strain exercised by the very elastic peripheral tissue parts of 
the bark body. These contract and become shorter if isolated. They 
uniformly grow shorter even in their natural position on the tree in the night 
because of a radial swelling resulting from the taking up of water-. 

Therefore, as the shoot grows, there develops a considerable longitudinal 
tension due to the struggle of the elongating force of the surrounding tissues, 
at times of the bark body, to contract both themselves and those surrounding 
them. The result of this struggle is evidenced in the length of the pith cells 
within one intemode. Cell measurements have shown that the pith cells are 
longer at first than they are later and that a very strong growth in breadth 
is associated with their subsequent shortening. 

This increase in breadth is the result of the ultimate preponderance of 
the peripheral strain. When the increase in length of the internode is 
complete, the cross tension becomes great. 

It is easy to understand that other strains must occur after the length- 
ening of a plant part is ended when one considers that the part of the trunk 
which has already elongated now thickens permanently and that this thick- 
ening depends upon the differentiation of the cambial cells, lying between 
the bark and wood, into new wood and bark elements of the following year ; 
the year old shoot forms new wood layers above those of the previous year; 
these new wood layers must make room for themselves under the girdle 
formed by the bark and its outermost cork layers. This can be done only 
by a distension of the bark mantle which, however, does not give way without 
resistance. This resistance makes itself felt in pressure and thus, during 
the period of the growth in thickness of a shoot, we find the tender tissue of 
the cambium pressed on one side by the mature but still distending young 
wood and on the other side by the constricting influence of the bark mantle, 
which gives way only to very strong pressure. 

Under this double pressure, the elements of the wood are formed from 
the cambium, that is, the elongated, thick-walled wood cells, poor in contents, 
or finally entirely empty, as well as the ducts and duct-like cells. 

De Vries"' has now determined experimentally that the cells of the wood 
become narrower (and the ducts fewer) the greater the bark pressure. He 
increased the constricting effect of the bark mantle by putting on a firm 



1 According- to Kraus (loo. cit., p. 141), Hales had already adopted the theory 
expressed by Borelli In his book "de motu aninialium" that "The young shoot grows 
and elongates by the spread of the moisture in the spong-y pith." 

2 Kraus, G., tJber die Verteilung und Bedeutung des Wassei's bei Wachstums- 
nnd Spannungsvorgang^en in der Pflanze. Bot. Zeit. 1877, p. 595. 

■" Hugo de Vries, tJber den Einfluss des Rindendruckes auf den anatomischen 
Bau de Holzes. Flora 1875, No. 7, Sanio, Bot. Zeit. 1S63, p. 393. 



774 

band and in other specimens weakened artificiallly the pressure of the bark 
by cutting it longitudinally. He thus succeeded in explaining what Sachs^ 
had already suspected, that the difference in the production of the annual 
ring is due to bark pressure, which changes regularly in the course of the 
year-. 

In the spring, at the time when the wood is most swollen because of 
its absorption of water, the bark pressure is very great, as may be noticed 
in the production at this time of new bark tears and the widening of those 
already present. During the unfolding of the foliage, the wood loses a 
great part of this water by evaporation. It then contracts, reducing the 
pressure of the distended bark. This explains the recognized formation of 
larger wood cells at this time. However, the more new wood is formed 
under the bark in the course of the summer, the greater will be its internal 
pressure against the underside of the bark; at the same time the bark layers 
lose a part of their elasticity because of drought and thus their resistance to 
the internal pressure of the wood becomes much greater. Under such 
increased pressure conditions, we find a production of narrow and broad 
celled, thick-walled autumn wood. 

Another point, which I had an opportunity to observe in artificially 
constricted places, is the increase of spiral twisting in wood elements due to 
the increased bark pressure. Finally, in the overgrowing of constrictions 
made by wires, this twisting is found to be so increased that, in a certain 
zone of the overgrowth callus, the wood cells which otherwise have a longi- 
tudinal course lie almost horizontal. A radial section, made directly above 
the overgrown wire ring, shows a zone of wood cells cut across instead of 
lengthwise. These fibres, running horizontally, gradually reassume their 
vertical, normal course when the swelling becomes less and passes over into 
the normal trunk. 

The increased twisting of the wood elements due to increased bark 
pressure explains also the well-known phenomenon, of the non-parasitic, 
tivisted growth, which occurs especially in dry, poor soils (with Syringa and 
Craetaegus) and has been observed in very different kinds of trees. The 
causes of the increase in bark pressure dififer in the different cases. 

The regular stratification in the wood body of the wide spring wood and 
narrow autumn zvood thus caused is only a special case of the law proved by 
De Vries, that an increase of the bark pressure produces narrow celled wood 
but a loosening of the bark, on the contrary, a wide celled wood. 

It is easy to convince oneself, however, by counting the cells after an 
artificial loosening of the bark, that this acts not only on the development but 



1 Sachs, Lehrb. d. Bot. 1st Edition, p. 409. 

2 Investigations by Krabbe, published later (Sitzunssbericht d. Akad. d. 
Wissensch, z. Berlin, 14. Dez. 1882; cit. Bot. Zeit. 1883, p. 399) .on the relations of 
bark tension to the formation of the annual rings and displacement of the medullary 
rays led to the conclusion that no effect on the annual ring formation could be 
ascribed to the radial bark pressure, on account of its insignificance. To me, the 
method used does not seem free from ciitici.sm, so that some doubt of the correct- 
ness of the result is justifiable. 



775 

also on the number of the cambial cells. The less the hark pressure, the 
(jreater is the number of cell divisions in the direction of the radius of the 
trunk; the greater also the elongation of the individual cells and ducts in a 
radial and tangential direction, the lesser, howez'cr, in a longitudinal direc- 
tion. This change in the dimensions increases to such an extent that in 
those places where the bark pressure is almost entirely removed the thick- 
walled, elongated wood cells are found to pass over into short parenchy- 
matous cells. In this, the differentiation of the tissue into cells and ducts is 
lost. Only a uniform parenchyma wood develops. 

A work by Gehmacher^ takes up the influence of bark pressure on the 
structure of the bark itself. His investigations lead to the conclusion that 
the greater the pressure, the fewer the cork cells formed and, conversely in 
the same way, the radial diameters of the individual cells differ. The cells 
of the primary bark parenchyma seem contracted not only radially but also 
laterally. Their form is, therefore, angular while in those produced under 
less pressure it is spherical with considerably larger intercellular spaces 
(which can disappear entirely under strong pressure). The number of bast 
fibres is said to increase considerably with a reduction of pressure (which I 
have not observed myself) and to decrease almost to disappearance with an 
increase of the bark pressure. 

Nordlinger- also considers the production of a wavy periphery of the 
wood body, instead of the regular spherical one, to result from bark pressure. 
Where the wood seems indented the bark frequently appears thicker. The 
strongly developed groups of stone cells are said to be the ones which are 
pressed by the bark into the cambium and arrest the growth of the opposite 
part of the wood. 

If we now give credence to the circumstance to which Kraus'' calls 
attention, that part of the cell content is more quickly pressed out from the 
cell tissue under increased bark pressure, possibly toward those places in 
which the bark pressure is less, it can be no surprise that a large amount of 
reserve substances are found stored in the porous parenchyma wood, formed 
from the cambium as a result of the reduced bark pressure. The wide- 
lumined, thin-walled parenchyma wood is the most accessible center of 
deposition for the constructive material flowing toward it. For this reason, 
we see that where the wood cylinder forms parenchyma tissue instead of 
prosenchymatous elements, this usually (with the exception of the young 
callus rolls) is richly filled with reserve substances for a large part of the 
year and, in fact, in our trees also containing starch. 

All the wounds to the tree trunk bring about a loosening of the bark. 
Nevertheless, the wood, formed in healing the wound, must vary in structure 
so much the more from normal wood and take on and retain so much the 



1 Aus Sitzunssber. d. Wiener Akad. d. Wissensch. Vol. LXXXVIII, pt. I; cit. in 
Botan. Central!)!. 18S3, No. 47, P. 228. 

- Niirdlinsei', W'irkuns' des Rindendruckcs. Centralbl. f. d. gesamte Forstwesen. 
W^en. OctolDer issue, 18S0, p. 407. 

- Loc. cit., p. 138. 



77^^ 

more the characteristics of parenchyma wood, the less the pressure of the 
bark g-irdle on the cambium at the time of ringing and the longer this loosen- 
ing lasts. 

We have seen in canker wounds how this porous structure at the edge 
of the wound causes more and more a new loosening of the bark, a new 
excrescent production of porous tissue and the final exhaustion of the 
branch, due to this production. 

Every overgrowth edge formed about open wounds on the trunk, there- 
fore, begins with the formation of short-celled, wide-lumined wood elements 
which, sharply bounded, lie against the normally exposed wood. The wood 
elements also pass gradually over into a normal structure, according to the 
increase of the overgrowth edges and, therefore, the stronger bark pressure. 
If, finally, the overgrowth edges coalesce and the bark again becomes a 
uniformly connected girdle around the trunk, or branch, the normal amount 
of hark pressure again sets in and with it the normal direction of wood 
cells and ducts. Every year normal wood is deposited above the closed 

wound. 

Scarification Wounds. 

The best example of the changes in tissues during the process of wound 
healing is found in the cicatrization of scarification wounds. By the term 
"scarification," as is well known, is understood the cutting through the bark, 
lengthwise of the stem, down to the wood body, without the removal of any 
substance. If the tree is slit in this way, the edges of the wounds pull apart 
(Fig. 173). Naturally, the two edges of the wound are nearer at the end 
of the incision (Fig. 173 a). The process of healing is completed most 
rapidly there. Fig. 174 shows the cross section of a healed incision on a 
sweet cherry tree, from the end of the wound, i. e. from the region marked 
a. We see at h the old wood, which was cut at w, and shows that part of 
its ducts and wood cells died because of the effect of the air. The cambial 
zone (c) which at the time the incision was made lay above h has formed, 
during the process of healing, new bark {nr) and new wood {nh). The 
newly formed wood zone, however, does not resemble the normal wood 
produced beneath the uninjured bark either in position, or in structure. 

It forms one part which, projecting outwardly, is three-cornered in 
shape, its highest point coming nearest the groove {s) formed by the previ- 
ous incision. This three-cornered convexity is caused by the development 
of parenchyma wood {hp) which exceeds that of the tissue lying farther at 
the side. This production of v(^ood was the first activity of the two edges of 
the cambium which were separated by the incision {s). Here the bark 
pressure was the weakest, the cell increase the greatest, but the elongation 
the least. Only after the new bark, formed from the young, inner bark and 
the cambial zone, has attained at j a greater power and greater resistance 
because of the newly produced cork layer {k') does the bark pressure 
gradually increase. Its influence on the cambial zone producing the wood is 
stronger and the form of the wood elements gradually becomes more like the 



777 

normal. The part hp passes over gradually into the regular wood much 
more distinctly divided by medullary rays (m). The transformation of the 
bark elements, taking place parallel to the change of the wood elements, will 
be described more in detail in the callus rolls due to girdling. 

When the trunk grows further, the cambial zone (c) always deposits 
new normal wood and new bark with hard bast {hh) above the wound sur- 
face and when finally the old parts of the bark {ar')^ separated by the pre- 
vious incision, with their cork zone {k^ and the dead wound edges of the 
bark formation (/) which have been separated by the cork zone of living 
tissue, die and scale ofif, the wounded place externally becomes smooth and 
even. 

We will have to consider Fig. 175, if we wish to go somewhat more in 
detail into the beginnings of the process of healing. This represents a cross- 
section through a single wound edge of a place of scarification (Fig. 173 6) 

.■t 7c 





Fig'. 173. Scarification wound. Fig'. 174. Healed scarification wound. 



in the sweet cherry at a time when this edge had not yet united with the 
opposite one, growing from the other side of the wound. The wound sur- 
face (Fig. 175 w) has not yet been covered, h indicates here also the old 
wood which at w has been exposed by the incision. At the time the incision 
was made, the knife passed from s to zv. The old bark {ar) was drawn 
back towards the sides from this plane of incision. This part corresponds 
to that similarly indicated in Fig. 174. The upper part of this old piece of 
the bark, as well as the edge, which has dried out because of the incision 
(Fig. 174 t), is indicated in Fig. 175 by the contours marked t and only one 
hard bast bundle {hh) has been sketched in the bark parenchyma {ar). At 
the time the incision was made, the cambial zones (c) and the young inner 
bark {ir) lay close to the old wood {h). The cells which bounded the plane 
of the wound incision {s to w) reacted differently to the wound stimulus. 
The parenchyma of the older bark dried backward, for a certain distance. 



778 

and formed the brown, dry edge of the wound, recognizable to the naked 
eye, and thus enclosed each slit (Fig. 173 c). The parenchyma of the inner 
bark (ir), still capable of increasing, its growth not yet having ended, takes 
advantage at the edge of the wound of the opportunity of spreading toward 
each side where the pressure has decreased, that is, over the plane ^'to w. 
These cells, therefore, curve outward. Those from the cambial zone shove 
-ihe first bark cells further out and mature, in the subsequently growing zone, 
to bark cells (r) containing chlorophyll; and in this way the tender paren- 
chymatous edge of the wound (/, ir) is primarily produced. The peripheral 
cells (r) of the convex edge of the wound turn brown later and dry up. 




Fig-. 175. Overgrowth edge produced in a scarification wound. 

Cork (k) is produced in the cells lying directly underneath this. This cork 
zone (k to k), covering the whole wall of the wound, now attaches itself to 
the outer cork covering of the old bark so that the new structure is sur- 
rounded by a very inelastic cork layer which consequently presses on the 
swelling tissue lying beneath it. 

On this account, the bark pressure is also produced at intervals. The 
influence of this bark pressure on the immediately succeeding products of 
the cambial zone (c), which is bent forward like a snail but does not reach 
to the old wood (h), manifests itself by the formation of thicker walled ele- 
ments. New wood {nh)is produced which toward the wounded side is 



PART X. 



MANUAL 



OF 



Plant Diseases 

PROF. DR. PAUITSORAUER 



Third Edition—Prof. Dr. Sorauer 

In Collaboration with 

Prof. Dr. G. Lindau And Dr. L. Reh 

Private Decent at the University Assistant in the Museum of Natural History 

of Berlin in Hamburg 



TRANSLATED BY FRANCES DORRANGE 



Volume I 
NON-PARASITIG DISEASES 

BY 

PROF. DR. PAUL SORAUER 

BERLIN 



WITH 208 ILLUSTRATIONS IN THE TEXT 






^\io 



Copyrighted. 1920 

By 

FRANCES DORRANCE 



> :' 



^Cf.A605088 
CxC 22 1920 

THE RECORD PRESS 
Wilkes-Barre, Pa. 



s 






779 

parenchymatous, short, with wide lumina (.r) and perforated by isolated, 
short, wide ducts {g). The further the new wood Hes from the edge of the 
wound, the more regular, narrow, dense and longer celled it is, the sharper 
appear the medullary rays (m) and their continuation (w') in the bark. The 
more gradual the formation of the new wood, the more taut is the tension 
in the outer cork zone (^ to ^) of the overgrowth edge. This frequently 
tears apart in places as a result of the inner pressure, so that the bark 
parenchyma is exposed and pushes out into the torn place. On these out- 
pushing cells, new cork cells are formed in the shortest possible time, which 
lie against the surrounding ones and thus close the cork girdle. 




Fig. 176. Cross-section through a hollow pine trunk 'in which only the circum- 
vallation edges, several years old, carry on the nutrition of the trunk. 

In case a scarifying incision is so broad that the overgrowth edge of the 
first year cannot cover it, the new wood of the following year will overgrow 
the wound surface like a lip. In this lip-like, convex overgrowth, which is 
recognized best by the course of the new covering cork zone {k to k, Fig. 
175) the cambial zone (c) assumes a special curvature, which becomes more 
marked the deeper the wound surface lies. If it now happens that, in old 
trunks, a broad longitudinal wound is made, instead of a scarifying one, and 
the wound body is destroyed by atmospheric influences, together with para- 
sitic action, so that the trunk becomes hollow, ultimately only the overgrowth 
edges will remain. Fig. 176 represents such a case. It is a cross-section 
from a hollow pine trunk^. Because of the slow rotting away of the 

1 The oi'iginal may be found in the Botanical Museum in Berlin. 



78o 

younger annual rings, the overgrowth edges have assumed a beautiful, 
spiral form, rarely to be observed, and the nutrition of the trunk depends 
on the comparatively slender v^ood layers of the last few years. The 
process is shown in less striking form in all hollow trees, for example, often 
in willows and poplars. In conifers, the rotting away of the trunk, as a 
result of longitudinal wounds, is a less frequent case, because the wound 
surface usually coats over with resin, or at least the parts of the wood 
exposed become resinous. This self protection, after a longitudinal injury, 
becomes most apparent in the gathering of resin, as Fig. 177 shows. 




Fig. 177. Section of a trunk of Picea vulgaris with the overgrowth of the resin 
channels. The entire age of the tree is 70 years. The first resin tapping (a) took 
place at the age of 50 years, the second (b) at 51, the third (c) at 62, and the fourth 
(d) at 65 years. (After Dobner-Nobbe.) 



The wounds resulting from the gathering of resin, in the form of strips 
some centimeters broad and about 2 m. long, from which the bark has been 
removed, do not die for some time. In spruce trees, R. Hartig found that 
the turpentine flowed in drops from the resin canals, lying in the medullary 
rays, soon after injury. Although a large amount of resin is accessible to 
the wound, since the resin canals running vertically in the trunk are in open 
connection with those of the medullary rays, yet the very fluid turpentine, 
as a rule, ceases to flow after the first year. The turpentine becomes thicker 
by the volatilization of the turpentine oil and the turning to resin (oxida- 



78i 

tion). After the resin has been scraped off from both sides of the tapped 
place, the overgrowth roll is cut away in order to open new resin canals, or 
new strips of bark are removed from other sides of the tree. 

Inscriptions. 

Inscriptions and numerals cut into the trunks of trees, as also the 
irregularly gnawed and bitten places produced by the gnawing of wild 
animals in winter, should be mentioned as special cases of a common form 
of longitudinal wound extending into the old wood and connected with a 
loss of substance. 

In inscriptions, the knife has removed considerable amounts of old 
wood and, therefore, has penetrated deeper into the trunk; on the other 
hand, however, the wound is not so broad. The healing of deep incisions 
begins at the longitudinal edges of the wound; the upper and lower edges 
share only to a very insignificant amount in this. The edges of the wound, 
produced by the cambial zone and provided with their own bark, extend 
further every year, forming overlapping layers, and thus gradually grow 
over the wound surface without becoming re-united with the old wood, of 
which the outermost cell layers, bounding the wound, turn brown and die. 
These healing layers form only a mass lying close against this wood, like 
the metal in a mould. At the moment when the two opposite edges of the 
wound of each letter coalesce, i. e. their cambial zones unite, these zones 
again form normally arranged wood elements, which become increasingly 
thicker because of the annual zone of increased growth, and thereby leave 
the original incision deeper and deeper in the trunk. In splitting the wood, 
a lucky blow will separate the intermediate layers, which had not been 
injured, between the individual letters or numerals, and the original brown 
mould falls away from the in-grown wood mass. 

Injury Due to Wild Animals. 

In injury due to wild animals, the wounds are broader, more irregular 
but, as a rule, extend only into the sap wood. 

If the bark and sapwood are torn oflf from the entire circumference of 
the trunk, it dries up after a number of years, if the injury did not occur 
early in spring or in summer. As a rule, however, the grtawing and barking, 
due to wild animals, takes place only on scattered parts of the trunk and 
then there follows gradually a formation of overgrowths from the edges of 
the remaining bark. If such overgrowth edges are injured again in some 
subsequent year, before the first wound is closed, the wood body apparently 
takes on a very complicated formation of annual rings. 

The injuries differ with the kind of animal. According to Ratzeburg^, 
red deer and elk, but not the roebuck, "peel" the tree, since usually in the 
spring, in feeding, they loosen strips of bark at the bottom by means of their 
incisors and then tear them oft" upward. The healing then takes place either 



1 Waldverderbnis, I, p. 50 t£. 



782 

by overgrowth or, in some cases, by a new formation of bark (cf. Barking 
of Fruit Trees). The bark may also be worn off by rubbing and blows, 
but in this the half-loosened remnants remain on the edges of the uninjured 
bark in the form of tatters, or small rapidly drying and, therefore, curling 
strips. Usually the traces of hair on the bark remain. Since deer and 
roebuck rub their horns up and down against the tree, to free tliem from 
the velvet, these rubbing wounds are longer than the peeling wounds and 
more frequently extend around the trunk. Now, the roebuck sheds its 
velvet in February and March ; the deer about the first of May, and others 
four weeks later. The wounds, due to the latter, therefore, fall in a time 
when the tree has the greatest amount of plastic material at its disposal. 
They will, therefore, heal much more quickly than wounds made in the 
winter and spring. It thus happens that the wound does not once reach 
the cambium, but only removes the outermost bark layers. If the inner 
bark remains in place the annual ring develops almost normally beneath it 
from the cambium, at least, so far as the arrangement of wood and vascular 
elements is concerned. The wood cells, however, are usually thinner 
walled, with broader lumina, the ducts much more numerous, the whole 
annual ring broader. If the weather is wet, or the habitat of the trees 
shady and damp, a callus tissue frequently develops on the outerside, from 
the cells -of the youngest bark which has been left in place. This callus 
tissue leads to the formation of new bark ; in rarer cases, with luxuriantly 
growing trees, to the formation of isolated wood bodies. 

Wounds from blows and splitting of the bark also arise at the time of 
"rubbing" and in the period of "heat" in the late summer. A different 
method of healing the wounds now often sets in, since a callus tissue is 
formed from the youngest sapwood layers on the wood body, which has 
been freed from the bark; it fills out the hole, as in budded trunks (cf. 
Budding). 

We have still to consider gnazved wounds, as produced by mice and 
rabbits, beavers and hares. The latter, with their teeth, cut young branches 
or weak plants. Real gnawing, which is so disastrous for our fruit trees, is 
found usually only after deep snows. The wounds extend to the older 
wood on which may be recognized the tooth marks. If these reach around 
the trunk in connected surfaces, the tree is lost. If, on the other hand, 
isolated particles of bark are left in place, an overgrowth takes place from 
these. 

According to v. Berg, it is advisable to fell Aspens and Sallows {Salix 
caprea), which game peels, at once, in order to protect the other trees from 
similar injury. Finally, the scattering of food, during the winter, might be 
cited as the best means of protection. We insert this chapter on the injury 
due to game only in its relation to the anatomical processes of healing 
wounds. This subject is treated very thoroughly in a recent work by 
Eckstein^. 



1 Eckstein, Die Technik des Forstschutzes gegen Tiere. Berlin 1904, Paul Parey. 



783 

In places where grazing cattle are driven into the forest they frequently 
cause greater injury than do game. Roots will be exposed to such an extent 
that whole trees die along the paths. Sheep and goats bark larches, firs and 
balsams, etc. As v. Mohl indicates, and Ratzeburg confirms, deciduous 
trees endure injuries to their trunks, extending to the cambium, much better 
than do conifers. 

Klein, in his latest forest-botanical note book^ gives numerous and 
good reproductions of trees that have been gnawed by grazing animals. 

Overgrowth of Cross Wounds in Many-year Old Trees. 

If branches, or trunks, are cut across the same processes of breaking 
the bark and the new formation of overgrowth edges must set in as were 




Fig. ITS. Remains oi a sawed off branch which had died back from the cut surface 
and which had been covered over as with a cap, by the overgrowth edges of following 

years. 

described above in scarification. The injury, however, in itself is much 

more dangerous because in this all the annual rings of the branch are 

exposed and the efifect of the atmosphere and wood destroying fungi is 

uncommonly facilitated. 

We see in the adjoining cut (Fig. 178) the product of several years' 

overgrowth of the old stump of a branch. The darker, central part is the 

cut end of the branch, which, under the influence of the atmosphere, has 

died far back into the trunk. In five years, the wood cap of the overgrowths 

1 Klein, Ludwig, Bemerkenswerte Baume im Grossherzogtum Baden. 214 Illus. 
Heidelberg 1908, Winters Universitatsbuchhandlung. 



784 

which have extended farther each year, has been formed over the surface 
of the wound and has finally closed it. The overgrowth in this case has 
taken place principally from above, since most of the plastic material has 
come from that direction. In a slender, longitudinal wound the overgrowth 
takes place principally from the sides. 

The process of overgrowth, which sets in in the branches of trees, also 
causes the closing of wounds on cut or chopped surfaces of stumps left 
when trees are felled. The process extends only comparatively slowly, 
since the cambial ring producing the overgrowth edges has to cover a very 
large wound surface. The result is that, long before the overgrowth edge 
has reached the central part of the cut surface, this has decayed and the 
center of the branch in consequence has become hollow. The overgrowth 
masses now sink down into the cavity in very different forms and, at times, 
in twisted cords covering projecting splinters or stones. Thus they can 
attain a considerable size^. 

The question is now pertinent, whence comes the material necessary for 
such an extensive new formation. The opinion usually expressed is that 
the reserve substances, formed before the felling of the tree and present in 
the stump, can be the only source of all the new structures. In other cases, 
root union, which occurs not infrequently, is used to explain this, for it is 
assumed that the stump is nourished by the uniting of its root branches with 
the stronger roots of adjacent trees, which still retain their crowns. 

Certainly, cases of this kind are not rare in larger tracts of trees" and 
such a nourishing trunk can actually give considerable assistance to the 
stump. Nevertheless, there also exist instances in which absolutely isolated 
trees have formed such large overgrowth masses on the stump that the 
supposition of a production of such massive new structures from the reserve 
substances alone does not seem sufficient explanation. 

In my opinion, however, there exists universally in such cases an acces- 
sory apparatus, which is capable of conveying newly assimilated material. 
If the young overgrowth edges are investigated more or less chlorophyll 
will be found in their bark, according to the amount of light the trees receive, 
and it is by no means clear, why this chlorophyll apparatus should not 
assimilate just as well as the green bark of the trunk. The fact that 
branches are found growing out of older overgrowth edges shows how 
abundant is the life prevailing in them^ 

The formation of branches from the cambial ring of tree stumps is a 
very common occurrence, which comes to view on all sides with felled 
poplars and arises from the production of adventitious buds in the paren- 
chymatous overgrowth tissues. 



1 Good illustrations of such cases in Goppert, Nachtrage zur der Schrift iiber 
Inschriften und Zeichen in lebenden Baumen. Breslau, Morgenstern 1870, 

2 Goppert, Beobachtung-en iiber das sogen. fjberwallen der Tannenstocke. Bonn, 
Henry & Cohen, 1842. 

3 V. Thielau, in Lampersdorff near Frankenstein in his advertisements of the 
Goppert Treatise (tjber die Folgen ausser-er Verletzungen der Baume, etc.) in May, 
1874. 



785 

Even ill the poplars a complete circle of strong green branches grows 
up around the edge of the cut wood body. Such an "eruption of shoots" 
degenerates, as a rule, after a few years because it is not able in its place of 
production between bark and wood to form new roots which can reach the 
soil. If soil reaches the base of these shoots by being covered or by prema- 
ture decay of parts of the bark, the shoots can free themselves from 
the nutritive trunk by growing roots and form long lived, independent 
individuals. 

The ability to produce new shoots from the tree stump, very differently 
developed in different tree genera and very rarely in conifers, does not 
always depend on the formation of adventitious buds but also on the awak- 
ening of dormant eyes as in conifers. In this, however, the hard cortex of 
the stump often hinders further development. 

If such a subsequent development of shoots is expected and desired, as 
in forestration or in parks, the trees must be cut down as deep as possible 
in order to give the new shoots a good chance to root. 

The custom, not infrequently found, of renewing tree plantations by 
leaving stumps one meter high, should be given up absolutely. The new 
shoots developing on such stumps are, on an average, much weaker and are 
often surpassed by shoots at the surface of the soil. 

Overgrowth Processes in Year Old Branches. 

In our cultivated trees, the necessity arises of cutting back the tops in 
order to prune the foliage shoots and thus favor the fruit buds, or in trans- 
planting to bring the top into balance with the injured root system. The 
pruning affects principally the year old growth, and is done either in the fall 
or early spring. Consequently, a considerable time passes before the 
processes of closing the wounds begin through new formation of tissue. In 
this it is found not infrequently that such young growth dies back for a 
short distance from the cut surface. 

In Fig. 179 is shown the tip of a year old cherry branch which has 
dried back some distance from the cut surface. Fig. 180 shows the same 
branch cut through longitudinally ; j to / is the original cut surface ; t is the 
boundary layer, back to which the twig has died; a, a swelling frequently 
found in such cases. Fig. 181 shows the anatomical structure. In it, s to / 
is the plane of the cut, a h, the last peripheral particle of the old wood of the 
cut surface; a r, the old bark with its outer normal cork layers {k). Of 
this bark, the tissue indicated by T has dried back and, in fact, the tissue 
near the hard bast cords {b) dies the furthest downward; the bast cord is 
also dead and together with the outer cork layers of the bark, which also are 
but little shriveled, projects from the discolored parenchyma. The cut 
surface is, therefore, uneven and rough. 

The next process which sets in, after injury and after the upper bark 
tissue has died, consists in the cutting off of the dead from the healthy tissue, 
by means of the formation of a cork zone {k' , k"). The cork zone is devel- 



786 



oped more extensively about the base of the bast bundle and represents a 
radiating overgrowth (k"). The increase in cell numbers begins at once in 
the layers of the cambial zone (c) lying next to the cut surface, and of the 
bounding, inner bark which, at the time the pruning was done, lay close to 
the wood body (a h). 

Exactly as in the protuberance of the roll in the scar wound shown in 
Fig. 173, the protruding bark zone (n r) is formed from the products of the 




Fie;. 179. 





Fig. lyi. 



A one year old branch of the sweet cherry cut through in cross-section, the cut 

surface of which has dried back. 
Fig. 179. From without the cut surface of the branch appears somewhat dried back and has a swelling (a) 
below the dried tissue. Fig. 180. The same branch cut through in the median line. Fig. 181. Anatomical 

sketch of the region a to s> of Fig. 180. 

cambial zone and the young bark, and this protuberance is closed in the same 
way by a cork girdle {k' k"'). The wood products of the cambial zone, the 
maturing of which changes gradually because of the pressure of the newly 
produced wound bark, are produced at first as parenchyma wood {hp) in 
which cord-like, short, porous duct cells {g) occur. The further the for- 
mation of the new wood, produced after injury, is traced back from the cut 



787 

surface, the more the elements of this wood are found to resemble the 
normally elongated, thick-walled elements {g', h'). In the drawing, the 
transition from the short vascular elements to the long ones is interrupted 
by the continuation of an old medullary ray (w) into the medullary ray 
{m) of the new wood. 

Besides this formation of new wood and independent of it still another 
cell increase manifests itself in the bark near the hard bast bundle. The 
parenchyma cells divide and increase, thereby, the thickening of the original 
bark, which is forced out by these new growths and causes the externally 
visible swelling (Figs. 179 a, 180 a, 181 a). Under certain circumstances, 
the new growth within the bark is so intensive that a meristematic zone is 
produced, which remains active for some time, producing in turn wood and 
vascular elements, and gives rise to the formation of wood fibres in the 
bark, said to have been found in the production of gnarl tubers. 

The drawing of a cut branch, reproduced in Fig. 181, does not agree 
entirely with the structure found in the overgrowing cross-wound of the 
stump of a branch. The reason for .this is that we usually think of such 
cuts as having been made late in the spring or summer on older branches. 
In these cases the drying back of the tissue from the surface of the wound is 
not extensive until the time when the wound begins to heal, i. e. until the 
formation of the overgrowth edge {nr, nh). This overgrowth edge soon 
appears above the cut surface and lies in a curve over the old wood, which 
had been formed before the time of pruning and is indicated by ah. The 
arrangement of the elements then corresponds to the formation of the callus 
roll in the cuttings illustrated in a later figure ; the nature of the cell elements 
remains that shown in Fig. 181. 

As the branch becomes older and the wood layers, formed from cambial 
zones, become increasingly thicker, the overgrowth edge, projecting on all 
sides above the cut surface of the branch, also becomes thicker and thicker 
until the opposite sides touch one another and unite in a cap which entirely 
encloses the cut surface. 

Each overgrowth edge begins in the way shown in cross section in Fig. 
175. It can, therefore, be said, figuratively, that the new wood layers, 
formed after injury, spread over the old wood body, laid bare by pruning, 
and finally shut it in by a cap. 

Girdling Callus. 

By "girdling" is understood the removal of a small circular strip of 
bark around the whole axis, usually at the time of the greatest cambial 
activity, since only at this time can the bark body be loosened easily and 
completely from the wood. 

In girdling, only the part of the branch lying above the wound receives 
the plastic material prepared by its leaf apparatus. This cannot, as des- 
tined, be used to strengthen the wood ring for the whole length of the 
branch, but is held back above the place of girdling, thus conditioning a 



788 

more abundant cell increase in the cambial ring at that place. We find that 
the diameter of the upper part of the branch has strikingly increased in pro- 
portion to that lying below the girdling cut. The supply of water carried 
up from the roots to this place is at first, however, considerably decreased. 
In the first place, the amount of water ascending in the bark is prevented 
from rising further by the girdling cut, and then the main stream, ascending 
in the wood, loses no inconsiderable amount of water at first by evaporation 
at the place laid bare by the girdling. Therefore, in the upper part of the 
branch the main factor of cell elongation, turgor, is decreased by the lessen- 
ing supply of water from below. The cell increase is indeed greater but 
the cell elongation is less than in the normal branch. While the growth in 
thickness of the part of the axis, which lies above the girdle, is increased, 
the apical growth of the branch remains moderate; the internodes are not 
as much lengthened. Shortening of the internodes with abundant supply 
of plastic material is the first step toward the formation of fruiting wood; 
thus fertility of the branch is more rapidly brought about by girdling. The 
part of the branch above the girdhng is demonstrably poorer in water; its 
leaves, likewise poorer in water, take on an autumnal coloration earlier, 
and the ripening of its fruit is hastened. 

The assertion that larger fruit can also be obtained by girdling has 
been confirmed only in certain cases. Grapevines, for example, and the 
American varieties especially, after girdling seem still to get such a consid- 
erable amount of water in the upper part of the vine that no retarding of 
the apical growth is noticeable. In this case, therefore, the development of 
the fruit depends essentially on the amount of plastic material and this 
varies in dift'erent years, according to the prevailing atmospheric conditions. 
In the same way, the character of the variety is of influence. For example, 
Paddock^ observed that the variety of grape, "Empire State," ripened its 
fruit three weeks earlier than usual because of girdling, the "Delaware," on 
the other hand, showed scarcely any reaction and, in fact, its quality was 
poorer. 

Girdling is used on grapevines as a means for curing the dropping of 
the young berries", but as a constant regular treatment in cultural pruning 
girdling will never find an opening; it may always be used only as a drastic, 
exceptional method, in special cases, the injuriousness of which frequently 
exceeds its usefulness. 

Even in the grapevine, in which girdling is used most frequently, its 
use must remain limited. In the "Annalen der Oenologie"^ Gothe judges 
that the hope of a general application of the process in grape culture will 
not be realized. The advantage of hastened ripening, he thinks, is unmis- 
takable. In this way, late varieties may still be brought to ripening, but 
the grapes of girdled vines give a worthless wine. The part of the vine 

1 Paddock, W., Experiments in Ringing Grape Vines. New York Agric. Exp. 
Sta. Bull. No. 151, 1898. 

2 Jager, Obstbau 1856, p. 125. 

3 Vol. VI, 1877, Part 1, p. 126. 



789 



above the girdled place dies (at least in European varieties), the part below 
it is poorly nourished, so that the eyes remain sterile and should not be taken 
into account in pruning. Besides this, girdled shoots break off very easily. 

In many trees also there is found frequently a hastening of the develop- 
ment of the leaf buds below the place girdled, which can increase to the 
formation of water sprouts. This case is more frequent in apple trees 
than in pears. 

Recently, girdling has also been made use of in herbaceous plants with 
edible fruits. Thus, for example, DanieF obtained larger fruit with the 
Solaneae by this treatment. Other observers could not 
confirm this, but found a retrogression in the develop- 
ment of the whole plant". 

If we now pass over to the study of the anatomical 
conditions produced by the girdling cut, or "pomological 
magic ring," by means of the adjoining illustrations, we 
shall, we believe, best further thereby an understanding 
of the matter by giving first of all a general description 
of Figs. 182 and 183. 

Fig. 182 represents a girdled grapevine; u is the 
lower overgrowth edge, u the upper edge ; bl, the bared 
surface of the wood body. 

Fig. 183 is a longitudinal section through the lower, 
smaller overgrowth edge (Fig. 182, m). S,S' is the plane 
of the lower knife cut in girdling; S,S'C' is the protrud- 
ing tissue of the overgrowth edge. H represents the 
outermost layer of the exposed wood body ; in this, g,g' 
indicates the ducts and h,h' the porous wood cells. R, 
as in Fig. 182, is the bark cut through in girdling, 
which appears pushed back from the wood by the out- 
swelling overgrowth tissue (r,C,C). This tissue at 2' 
lies close against the wood and is protected externally 
by a cork layer (k,k'). This protruding overgrowth 
edge of parenchymatous tissue is differentiated by the 
arched cambial zone c,c,c', into the parenchymatous 
wound wood (zvh) and the wound bark (wr). Both 
are traversed by radiating medullary rays (w). 

Figs. 184 and 185 show how such an overgrowth edge appears in cross 
section. The first was taken from the upper wound wall, close to the place 
where it leaves the bark ; the second figure originates from a broader, most 
distant region. 

In considering Fig. 183, we see that a mass of tissue has protruded 
from the edge of the wound produced by a 3 to 4 fold division of the 

1 Daniel, Lucien, Effets de la decortication annulaire cliez quelques plantes 
herbacees. Compt. rend. PaiMs 1900, p. 1253. 

2 Hedrick, Taylor and Welling-ton, Ring-ing herbaceous plants. New York State 
Agric. Exp. Sta., Geneva, Bull. No. 288. 1906. 





y^A 




\ 


Wk 








V 


^" 




\ 


'^'L 


W^^ 


f 



Fig-. 182. A ring- 
ing- -wound on a 
grapevine -witli the 
upper, more 
strongly developed 
overgrowth edge 
(u') and the more 
weakly formed 
lower one (u). 



790 

cambium and having at first the character of callus'^. This holds good for 
the products of division of the youngest bark, which united with the cambial 
callus from the later overgrowth roll. 

At the time of girdling (in July) the old wood body of the vine (Fig. 
183, H) was already strongly developed. We can recognize elongated, 
thick-walled wood cells in the immediate proximity of the ducts (g), chiefly 



^i ._ 




Fig. 183. 



Longitudinal section through an overgrowth roll which has developed 
from the lower edge of the ringing wound (Fig. 182, u). 



provided with horizontal cross walls {K), otherwise usually pointed like a 
wedge and having fine pore canals (/i'). The narrower vessels are spiral or 
ring ducts (^r) ; the wider ones show circular or slit-like pits (g''). The 
broadest of all have a ladder-like, or reticulated, porous wall. The ladder- 



1 All juvenile cicatrization membrane with apical growth of its cell rows, no 
matter whether produced on a cut surface above or beneath the surface of the soil, 
may be called "callus." We will call the callus which has a bark, is lignified, and 
continues its growth by an inner meristem zone the "overgrowth edge." 



791 

like arrangements of pits corresponds to the pores of the cells surrounding 
the ducts in rows, the walls of which cells are pressed against those of the 
ducts. 

The lower cut, by which the ringed place was laid bare (Fig. 182 bl) is 
indicated in Fig. 183 by the plane S,S'. In this longitudinal cut, therefore, 
the girdled exposed surface extends from S upward along the exposed wood 
cells. At vS", we see how the knife has smoothly cut the bark (R) perpen- 
dicular to the longitudinal diameter of the vine. At the time the cut was 
made, the bark (R) lay close against the wood (//). The tissue lying 
between them and projecting far out (r,C,C') has been produced after the 
girdling. And, indeed, the extreme lessening of the bark pressure con- 
nected v/ith the removal of the bark in the sectional plane S,S' and the parts 
adjoining it in the cells of the cambium, as well as in those of the youngest 
wood, likewise in those of the younger and youngest bark, causes a forma- 
tion of callus with a surprisingly great cell increase, since the end cells of 
the tissues named and those directly adjoining them push outward, divide, 
elongate and cut off their anterior ends by cross walls. In these anterior 
ends, the elongation and construction is repeated many times. In this way, 
a callus wall (C,C') projects in a circle, around the cut edge of which the 
inner side at / lies close against the wood, without uniting with it. 

At any rate, this callus wall at first has neither the extent nor the 
structure given it in the drawing ; this represents rather a wound wall devel- 
oping from the callus which, by the increase of the new cambial zone (c), 
has already formed secondary elements of thickening. Originally this callus 
wall consisted only of thin-walled parenchymatous cells (2,2) appearing 
immediately and radially arranged, their diameter in all directions being 
almost equally long. 

In such a juvenile callus wall, which is early differentiated, a cork zone 
is formed {k,k"') first of all on the outer circumference. It gradually 
increases in thickness and serv^es as a layer protecting the thin-walled, 
newly formed tissue mass. The cut surface of the old bark tissue {R) 
which has been separated widely from the wood by the new wound tissue, 
is cut off in the same way by the cork layer {k"). The old, hard bast cells 
(h), which have been cut, have turned brown from the cut surface deep 
down into the healthy tissue and died. The original bark tissue (r) lying 
inside and back of these bast cells has participated in the cell increase and 
callus formation; only the cells lying next to the hard bast of the original 
bark have formed a cork zone {k"'), cutting off the dead part. Near this 
cork zone run the hard bast cells {b'), which were already formed at the 
time of girdling, but under the influence of the cut do not extend normally 
as at b. The elements of these cells arranged in rows may be traced back- 
ward into the healthy tissue and gradually pass over into the old bast ; this 
row of cells is continued in the wound wall in the elongated, but very thin- 
walled groups of cells {b"), which lie at equal distances from the cambial 
zone. 



792 

The cambial zone, which runs close to the prosenchymatous wood 
elements in that part of the normally developed vine which lies below the 
place of the cut, describes a wide circle c,c,c' at its entrance into the wound, 
or overgrowth wall; it divides the apparently uniform ground tissue into one 
part lying against the old wood body of parenchyma cells with strong, porous 
walls, the wound wood (wh), and an outer part, the wound bark (wr). In 
the clearly marked, radiating arrangement of the individual cell rows, this 
row is recognized as a secondary growth of the cambial zone, appearing 
very early in the callus roll. The elements formed from the cambial zone 
have approximately the same parenchymatous form in the same horizontal 
surface, only, as already said, the parenchymatous wood (wh) differs from 
the bark tissue by its porous walls, which are more greatly thickened and 
more dense and, therefore, lie against one another with sharper angles ; a 
stronger pressure has already made itself felt here. 

But an evident differentiation is noticeable in the bark tissue itself. 
Between the somewhat oval cells, forming the ground mass of the bark, we 
find more elongated, more slender, somewhat prismatic cells arranged in a 
curve (b") approximately parallel to the cambial zones. These represent 
the very beginnings of the hard bast cells. They are richer in content and 
accompanied by pouch-like cells, which, in their longer axis, usually run 
parallel to the young bast bundles and contain raphides of calcium oxalate 
(o). The bark tissue produced from the youngest bark already formed at 
the time of cutting and containing thick-walled, but short and broad hard 
bast contains its calcium oxalate in the form of stellate druses, or separate 
crystals, similar to those which occur chiefly in the normal bark (o'). At the 
place of the transition, raphides and stellate druses are often separated from 
each other only by two cells. Here also only the loosely constructed tissue 
contains raphides. 

The parallel arrangement of the crystal-containing cells, with the bast 
fibers, is seen best in tangential section in the cherry ; here the base bundles, 
lying in a net work upon one another, are found to be accompanied by 
parenchymatous cells lying close against one another and elongated. Almost 
every one of these contains a crystal of calcium oxalate. In the grape this 
is less sharply marked and becomes relatively indistinct as the tissue, as a 
whole, loses its differentiation in the overgrowth walls. In this less differ- 
entiated part may already be recognized thicker walled elements lacking the 
deposition of calcium oxalate in the surrounding tissues. The calcium 
appears in the cells formerly filled with starch, a fact which indicates that 
the calcium oxalate is one of the end products in the solution of the carbo- 
hydrates. 

Therefore, no calcium oxalate is found in the outermost peripheral 
zones of the overgrowth edge because these zones consist of the first formed 
tissue of the quickly growing undifferentiated callus projecting beyond the 
cut surface. In these the material has been utilized entirely for cell increase 
and is not deposited in the end as reserve starch. On the whole, however, 



793 

only a few peripheral cell rows always remain free from starch and free 
from subsequently formed calcium oxalate, for the tissue which extends 
beyond the cut surface, and which warrants the name "callus" only so long 
as it is absolutely undifferentiated, soon shows a difference in its structure 
and passes very rapidly from the callus stage into that of the overgrowth 
edge. Soon after the formation of the peripheral cork covering, a meristem 
zone appears also in the interior of the callus tissue and represents the 
continuation of the cambial ring of the normal piece of the vine within the 
overgrowth edge. Besides this meristematic zone, the first traces of a bast 
body may also be recognized in the separated parenchymatous cells lying 
scattered close under the cork zone. These cells appear to have somewhat 
more strongly refractive, easily swelling walls (&"')• I^^ some of these I 
think I have recognized indications of sieve pores similar to those found in 
the tangential walls of normal bark sieve cells (ss), so that the conclusion 
may be drawn that the first differentiation of the callus tissue, appearing 
almost simultaneously with the formation of the new cambial zone, consists 
in the formation of sieve cells within the bark. 

The tissue formed in the cambial zone appears, in Fig. 183, to be divided 
longitudinally by the medullary ray cells (w). These are elongated radially, 
have clearer contents and like the rest of the tissue are small celled at the 
periphery of the overgrowth edge. Their approximately perpendicular 
direction changes gradually into the normal horizontal one as the rays 
extend into the normal tissue of the uninjured piece of the vine. 

In the youngest portion of the callus edges, where the tissue lying next 
the cork border first arose, one finds the wood lying between the clearer 
medullary rays to be short, thin-walled and parenchymatous. The further 
the wood is examined back toward the normal tissue, the longer and thicker 
walled it appears and it passes from its radial direction more and more into 
the longitudinal elongation of the normal wood elements. The earlier in 
the year the girdling is undertaken, i. e. the longer the newly produced 
cambial zone of the overgrowth wall produces wood, so much the more do 
the later formed elements approach normal wood in length and form. 

Scalariform vessels {g,^) appear in this thin-walled parenchymatous 
wood as the first thick-walled elements ; they have at first the size and 
arrangement of the wood parenchyma cells of the surrounding tissue but 
assume gradually the form and arrangement of normal vessels the nearer 
they approach the uninjured parts of the wood. In opposition to de Vries, I 
must maintain that the short duct cells are not always the first formed thick- 
walled elements. When the callus at the lower margin of a girdle is very 
weakly developed, the wood parenchyma often passes over directly into 
normally arranged, slightly thickened xylem elements, without the previous 
appearance of short duct cells. 

In the callus at the upper margin of a girdle which in the same length 
of time has developed more than twice as extensively as the lower callus, 
the cambial zone is broader, all the elements are more numerous and the 



794 



beginnings of the vascular bundles in the callus always start with duct cells. 

The formation of these cells takes place the earlier the nearer to the old 

wood they are formed. Their form, 
size, thickness of wall and arrange- 
ment will be more nearly normal the 
further back the tissue lies from the 
cut surface. The vascular strand (g,s) 
of this tissue grades gradually into the 
normal wood formed before girdling, 
thereby forming a pseudo-secondary 
growth in that area. 

According to the anatomical condi- 
tions shown in Fig. 183, we may say 
that the girdling has produced an un- 
usual loosening of the wood in the 
uninjured part of the vine adjacent to 
the wound. In this way the vascular 
bundles, which are formed of vessels 
and thick-walled tracheids on one side 
of the cambium and of the thick- walled 
phloem fibres and sieve tubes on the 
other, and which, in normal wood, are 
arranged close against one another in 
concentric circles, are separated and 
broken up into single strands by masses 
of parenchyma. These strands, g,2 
(vascular strands), and b' (phloem 
strands), the elements of which con- 
stantly become fewer in number, change 
constantly and continue into the callus, 
which is gradually covering the girdle. 

We may best see by means of cross 
sections taken at diiiferent heights 
through the callus, what happens to the 
vascular cylinder which in the unin- 
f) jured portion of the vine consists of 
the wood and the phloem rings, only 
slightly broken by few-celled medullary 
rays. This cylinder finally is separated 
into single strands by the growth of 
parenchyma induced by the girdling. 
The strands gradually become narrower 
as they pass outward radially and tan- 

gentially in wavy lines, they are at first distinct, but later anastamose forming 

a net and finally split up into isolated strands arranged in fans. 




Fig. 184. Cross-section through a ring- 
ing- roll close to the point where it 
appears on the plane S to S' in Fig. 183. 



795 



For the sake of greater clearness, the cross sections shown in Figs. 184 
and 185 have been taken from the upper similarly constructed but more 




.2* 



Fig. 185. Cross-section through the ringing roll at a considerable distance from the 

place of its appearance, i. e. where it is more luxuriously developed, as would be 

found in Fig. 183, possibly in the plane k to wh. 

strongly developed callus of the same vine, which furnished the longitudinal 
section, Fig. 183. 



796 

Fig. 184 shows the callus in cross section at the place where it leaves 
the old bark, i. e. about at 6" to S' in Fig. 183. Fig. 185 is a cross section 
through the middle of the projecting part of the callus, i. e. about in the 
place k to wh in Fig. 183. In Fig. 184, H represents a part of the old wood 
formed before girdling, g' indicates the wide, scalariform vessels of which 
those lying nearest the cut surface S to vS" have filled with tyloses (t) as a 
result of the injury, and consequently have become impervious to air; h 
shows the tracheids in cross section. S' to C (in Fig. 185, C to C) is the 
new wood formation of the callus. We find that the medullary rays (m), 
from the normal tissue (H), are continued, after a short interruption, into 
the callus. The medullary rays become constantly broader; the vascular 
bundles, the xylem elements of which in normal wood are closely packed, 
are separated further and further by the constantly widening medullary 
rays. The bundles thus have fewer elements and normal tracheids are no 
longer present. The strand (sf) consists only of short, wide vessels, and 
narrow ones with transverse walls, together with wide, thinner walled wood 
cells, abutting on each other transversely. 

The single strand in Fig. 184 (st) in the normal wood has divided in 
the tissue of the callus into two strands (st'), and these again into four 
strands in the part still further from the cut surface (Fig. 185 st'), at the 
same time the new bundles are pushed out of their original position by 
the formation of new medullary rays (Fig. 185 m'). They advance as 
separate groups toward the periphery of the constantly thickening callus. 
With the broadening of the tertiary medullary rays these thin vascular 
strands (Fig. 185 st'), which (in longitudinal section) seem to branch as 
they growth in length, separate farther and farther from each other until 
they finally disappear entirely near the outer edge of the callus. The 
terminals of these strands are short, broad, porous cells of wood parenchyma. 

It is well known that each vascular strand is made up of both phloem 
and xylem. The wood and phloem are sister elements^ In Fig. 184 b, we 
see a group of wood fibres, which belongs to the xylem strand st ; b' and bb' 
represent the phloem, belonging to st', the cells of which, analogous to wood 
elements, have become broader. The radial thickening of the phloem cells 
is not very well shown in the drawing. 

In the fall, when the grapevine has cut off the cortex by a cork zone, 
the sinuous cork layer (k), in the callus, has divided the phloem bundles 
into two parts (Fig. 184, b' to bb') ; c'c' represents in Figs. 184 and 185, the 
cambial zone. In Fig. 185, is a pouch cell with calcium oxalate in the 
form of raphides. In some pouch cells sharp, jagged very small protuber- 
ances project from the inner cell wall. 

The first differentiation in the callus may still be recognized after it has 
passed over into the finished overgrowth of the callus, beginning at the outer- 
most cork layer; i. e. if, in Fig. 185, the section begins at the part curling 
farthest downward and then advances upward. If we designate the part 

1 Ratzeburg, Waldverderbnis I, 70. 



797 

adjoining the old wood (Fig. 183, 2:' to S), as its innerside, in contrast to 
the spherically convex outer side, the parenchymatous tissue of the inner 
edge, lying directly under the cork zone, is seen even in the second sections 
to color more deeply when treated with iodine than does the corresponding 
part of the opposite outer side. In the same way, by using iodine, a radial 
division of the tissue may also be recognized, for certain bands at first only 
one to three cells broad take on a deeper color than the broader parts lying 
between them. A difference may be seen also in the form of the cells in the 
first cross sections, for those lying nearer the outer edges appear rounder 
than the more densely crowded ones nearer the inner edge ; also all the cells, 
lying directly under the corky outer layer, are smaller than those at the 
centre. The lighter colored bands contain cells with a greater radial elon- 
gation, the first indication of the medullary rays. The zone of the renewed 
cell division, which will form the beginnings of the later cambial rings, 
lies close to the inner side of the callus roll adjoining the region of cells 
which were the last to divide to strengthen the peripheral cork zone. From 
there, in the subsequent cross sections, the division zone moves farther and 
farther from the old wood (compare the curved course in the longitudinal 
section, Fig. 183, c to c'), reaching its greatest distance from the old wood 
outside the plane in which the girdling occurred and again within the old 
bark, approaching the normal wood until it takes up the usual position of 
norm^al cambium. 

The principles that have been discussed here in detail with reference 
to the grape are expressed in any kind of girdling, the special structure 
naturally varying with the kind of plant. 

Czapek^ has shown that, of the conducting elements, only sieve tubes and 
cambiform cells come under consideration for all assimilating products, 
indeed, the paths which convey substances are straight, even in the phloem. 
The phloem parenchyma, like the medullary rays, serves as storage tissue. 
The deposition of reserve substances is influenced by girdling, inasmuch as 
(according to Leclerc du Sablon") the roots of trees girdled near the base 
of the trunk in the spring at the time of sprouting are richer, and the trunks 
poorer, in reserve materials, than those of trees which have not been girdled. 
The leaves of the former to be sure are not so green, but contain much 
more reserve materials than ungirdled specimens and according to my obser- 
vations color much earlier in the autumn. 

Injuries to the Bark. 

A. Historical Survey. 

The processes of healing a wound which has exposed the wood all the 
way around the trunk often a meter in width, produced by the removal of 

1 Czapek, Fr., tJber die Leitungswege der organischen Baustoffe im Planzen- 
korper. Bot. Centralbl. 1897, Vol. 69, p. 318. 

2 Leclerc du Sablon, Recherches physiologiques sur les matieres de reserves des 
arbres. Revue generale de Bot., Vol. XVIII; cit. Bot. Centralbl. v. Lotsy, 1906, No. 
43, p. 447. 



798 

all tissue down to the cambium, have been the subject of observation for 
more than lOO years. 

Thus Treviranus^ quotes that L. Firsch found some apple and pear 
trees on an estate in the Province of Brandenburg, from v^hich all the bark 
had been removed from the points of insertion of the lowest branches down 
to the roots, completely around the trunk, so that the white wood could be 
seen everywhere. The trees were covered again with new bark. Frisch 
assures us that this experiment will always succeed if made at the time of 
the solstice and if the exposed outer surface, over which the sap is spread 
uniformly with a feather, is protected by linen or split cane against the sun 
and wind*. 

The celebrated experimenter, DuhameP, removed a ring of bark from 
several young trees, elms, plums, etc., 7 to 10 cm. wide down to the wood, at 
the time when the sap was flowing and surrounded the wounds with glass 
cylinders, which were closed at the top and bottom against the uninjured 
part of the trunk with cement and tissue. He found delicate, jelly-like 
warts forming on the exposed wood surface, and pushing out between the 
wood fibres of the sap wood (des mamelons gelatineux qui sortaient d'entre 
les fibres longitudinales de I'aubier). These little warts, which push out 
under very tender, probably left over, phloem lamellae, were at first white, 
and half translucent, later gray, and after 10 days (on April i8th) green. 
These new structures, broadened in the course of the summer and finally 
uniting, produced a rough bark beneath which delicate wood lamellae were 
recognizable. "Ainsi il est bien prouve que le bois pent produire de I'ecorce 
et que cette ecorce est des lors en etat de produire feuillets ligneux ..." 

Knight made similar experiments and obtained similar results. He 
found once^ on Ulmiis montana, a regeneration of the bark when the wound 
had not been covered. The tree grew in a shady place. Knight found in 
old topped oaks, with an incompletely formed new bark growth, that the 
jelly-like warts had pushed out from the parenchymatous cell tissue and "in 
many cases new bark was formed in small and isolated portions only on the 
upper surface." 

Meyen* quotes Werneck's observations, according to which the regen- 
eration of the bark will take place only if the barking happens about the 
25th of June, when the trunks are still young and the wounded place is 
"very carefully protected against drying by a hollow and closely adjusted 
bandage." 

We find Meyen's own theory'^ in the description of his experiments 
given in his Phytopathology. On April 30th, 1839, in warm sunshine he 

1 Treviranus, Physiolog-ie der Gewachse, Vol. II, 183S, p. 222. 

2 Duhamel, Physique des art)res 1758, Vol. II, p. 42. Vol. VII, p. 63, and loc. cit., 
p. 44. Vol. VIII, p. 66, 67. 

3 Treviranus, loc. cit, p. 223 (Beytr. 223). 

4 Meyen, Neues System d. Pflanzenphys. 1837, p. 394. 

5 Meyen, Pflanzenpathologie, published by Nees. v. Esenbeck. Berlin 1841, p. 14. 



* Miscell. Berolin. Contin, II (1727), 26. 



799 

removed the bark from the Httle trunks and larger branches of the hazlenut, 
the snowball, Syringa and willow and, like Duhamel, enclosed the barked 
places with cemented glass tubes, which in addition were wrapped with 
paper, although he made the experiments in thickly shaded places. Jelly- 
like drops were "sweated out" here also, "which always occurred on the 
places where the medullary rays appeared on the upper surface of the 
wood." 

Microscopic investigation of this "sweating" showed the warts to be 
composed of tender cell tissue, "which enlarged constantly because of the 
gum in the sap, exuded by the medullary ray cells." 

The greenish color, which these new structures assume, arises from the 
chlorophyll grains. In the course of the experimental year these structures 
reached a thickness of ii mm. but shrivelled greatly when dried. 

Meyen cannot ascribe the significance of bark to these new structures, 
which are also produced naturally in shady places^. For "no separation into 
dififerent layers, of which the normal bark of the same tree is composed, can 
be seen and moreover there is no trace of sieve tubes in it, which are, of 
course, very important ..." 

This physiologist, very distinguished in his time, who according to the 
Mirbelian theory considered the cambium to be a structureless sap, which 
brought forth such cell structures as those from which it had appeared, has 
indeed the merit of having made use of the microscope to investigate the 
new structures which appeared with the healing of bark wounds. He was 
not fortunate enough, however, to observe the production of wood among 
these new structures and to prove the analogy between these forms and 
normal bark. 

Probably the moist air and heavy shading from his cylinder were to 
blame, since as we shall see these factors influence considerably the charac- 
ter of the new structure. 

Dalbret- experimented earlier than Meyen, for on the 21st of June he 
barked an ash and a walnut, enclosed the barked places in a cylinder and 
obtained the same results as Duhamel. 

Th. Hartig^ in the spring of 1852 at the time the new annual rings had 
begun to develop removed the bark from 30 to 40 somewhat older oaks for 
6 to 8 meters above the ground and in August found the majority of the 
mutilated trees bore as dense foliage as the adjacent ones from which the 
bark had not been removed. On 5 or 6 young trunks a scabby eruption, 
pressed out from the medullary rays of the wood, had formed "curiously" 
only on the sunny side. Anatomical investigations showed that the erup- 
tion, quite independent of the phloem and cambium, had come from the 
wood alone and was a product of the medullary rays. 

1 Pflanzenphysiologie, Vol. 1, p. 390. 

- Journal de la societe d'agronomie pratique 1830; quoted by Trecul in 
"Accroissement des vegetaux dicotyledones ligneux." Annales des sciences natur. 
Ill, Serie, Vol. XIX, Paris 1853. 

3 Th. Hartig. Vollst. Naturgesch. d. forstl. Kulturpfl. Deutschlands. Berlin 1852. 
Explanation of the figures (plate 70, Figs. 1-3). 



8oo 

'The new structure begins with the appearance of a layer of cork cells 
at the periphery of the healthy medullary ray tissue, cutting off an outer, 
dead part. The living part of the medullary ray now develops several 
layers of parenchymatous cells about its circumference, which cells turn 
green like the medullary tissue already present. By the increase of the 
parenchymatous tissue around the medullary rays, a callus roll is produced, 
which rapidly becomes larger and constantly presses farther outward the 
cork layer which begins with the formation of lenticels. "The new cell 
tissue does not develop on any one place from the living medullary ray, but 
as everywhere new cells are formed in all places inside the cells already 
formed ; these reabsorb the mother cell, grow out to its size and widen the 
mass on all sides. In spite of the widening of the callus, due to the growing 
cell tissue, the living part of the medullary ray, nevertheless, always retains 
the same circumference, the same size, number, form and position of the cell 
tissue constituting it." 

"When the callus reaches a certain size, different parts become unusu- 
ally thick walled, as is also the case in the normal course of the life of 
the bark (stone cell aggregations). Further, on each side of the living 
medullary ray not far from its tip, a vascular bundle develops in the cell 
tissue, which consists of pitted tracheids and vessels between the medullary 
ray and the cork layer." By the fusion of the individual coordinate tissue 
zones of the new structures, which up to that time had been completely 
isolated and wart-like, a continuous bark layer covered with a cork layer is 
produced, differing only by the radial arrangement of its cell elements in 
cross section from the structure of the normal bark. "Along the sides of 
the tip of the medullary ray, the development of the wood advances up to 
the formation of a connected wood layer, traversed by the cell tissue of the 
old medullary rays just as by newly formed, smaller ones. The various 
wood bundles consist of tracheids and fibres. True spiral elements are 
lacking. A line of division between the wood and the bark (Meristem zone 
Ref.) is formed more and more sharply with the advancing development of 
the wood, although no trace can be discovered either of phloem fibres or 
of sieve tubes." 

Th. Hartig's observations, which represent an important advance, 
show, therefore, that the development of the new bark on a bark injury, 
takes place at the expense of the nutritive substances present in the wood 
and begins with the formation of a callus tissue around the tips of the 
medullary rays. 

It cannot be learned either from the description, or from the drawings, 
which cells initiate the callus formation. 

TrecuP fills this gap with his thorough anatomical investigations, which 
prove at the same time the participation of the whole young tissue left on 



1 Trecul, Accroissement des vegetaux dicotyledones ligneux. Annales des 
science, nat. XIX, p. 165. 



8oi 

the harked wood stem and not merely that of the medullary rays in the 
formation of callus. Nevertheless, under special conditions the medullary 
ray cells can alone cause the formation of callus and yet the case often 
occurs where the callus formation is initiated by the young wood cells alone. 

The young wood cells, the medullary ray cells and the narrow elements 
participate in the callus formation by a transformation into parenchyma 
cells which now increase in number^ 

The youngest cells, left on the wood cylinder, widen, elongate and 
divide. The end cell of the last row of callus cells becomes largest. It is 
often spherical, or club shaped, and the new cross wall is produced generally 
in this stage. The new end ceil now formed by the cross wall repeats the 
process. The older cells, lying back of it, elongate and divide. 

Besides this kind of callus formation, Trecul observed still another 
case. While the outermost remaining cells develop into callus tissue, by 
distention and division, it also happens that they show only a slight develop- 
ment, while the innermost young wood cells, lying beneath them, take over 
the role of the actual callus former. Trecul sketches (pi. 7, Fig. 11) a 
longitudinal section of the elm, the callus on the edge of which consists of 
short, isodiametric cells. This gradually drying layer has been pushed up 
from the wood by means of a thick callus layer, of which older cells now 
adjoin the wood. The youngest cells most distant from the old wood, 
lying directly under the outpushed dying layer, have stretched radially and 
formed radially parallel rows. 

Both cases of callus formation can occur at the same time in the same 
specimen. Probably the innermost layers of the exposed cambial body are 
incited to increase by the drying of the outermost layers. 

As my experiments show, all the cells of the cambial region can partici- 
pate in the callus formation, not only the young wood cells, as de Vries 
thinks, but also the young bark cells. It depends alone upon which cell 
layers are left when the bark is removed. If it is loosened in such a way 
that only a few of this year's sapwood cells still capable of increase remain 
on the old wood, the callus must be formed from them ; if, on the other 
hand, the very youngest cambium cells remain in place, they take over this 
formation of callus, while the underlying young sapwood develops, accord- 
ing to its position, into differentiated wood with vessels and is changed only 
in so far as all its elements become shorter, broader in the radial dimension 
and thinner walled. 

Trecul", in his Fig. 5, pi. 3, of a linden, gives the best example of this 
case. We will use this (see Fig. 186) to confirm our theory. B indicates 
the young wood of the current year formed before the removal of the bark. 



1 "Les fibres' ligneuses, les rayons medullaires et les vaisseaux d'un petit 
diametre eux-memes sont metamorphoses en tissu cellulaire proprement dit; car il 
y a une metamorphose reelle de ces organes elementaires en tissu utriculaire 
ordinaire, et ensuite multiplication de ces utricules nouvelles. 

2 Tr6cul loc. cit., p. 167. 



802 

with its vessels (v). A to A', according to Trecul, is the old bark of the 
previous year^. The split, which pushed up the bark, extends horizontally 
above the highest vessel {v) to the point marked x' ; from there it runs 
downward toward the right almost to the thin-walled, last-formed cells of 
the previous year, so that the whole group {g) should be considered as a 
new structure. At x, the loosened bark has removed only the outermost 
layers of the youngest wood, or has possibly extended only to the central 
cambial zone, so that the whole sapwood has remained in place. The 
outermost cells elongate (/) and divide (T). The upper cell (r) of each 
row, cut off by the new wall, repeats the process. 




Fig. 186. Callus formaton from young bark cells in a barked trunk. (After Trecul.) 



The young wood (sapwood) has been stretched radially by the injury, 
i. e. by the removal of the bark pressure. It forms shorter cells with wider 
lumens but has remained thin-walled, while the vessels already started have 
matured. 

From x' out, the young sapwood has been removed with the loosened 
bark and on the wood of the previous year only a few young wood cells of 
the current year were left. These cells have now taken over the formation 



1 It might seem strange that the annual ring at A' ends with a very thin- 
walled spring wood, but such cases actually occur. I obtained from the Eifel in 
January larches diseased with canker, the annual ring of which had formed over 
the summer wood a layer six cells thick of thin- walled spring wood. 



8o3 

of callus, which naturally lacks vessels, though it reaches the thickness of 
the adjoining parts by a more rapid increase in the lumen of the cells^. 

Opinions differ greatly as to the life period of barked trunks. 

The best example of an unusually long life period in trees which have 
lost their bark extensively, and have not replaced it, the exposed wood con- 
sequently falling victim each year to decay, is furnished by Trecul in his 
description of the linden at Fontainebleau'-. Yet we have still earlier 
observations. 

In 1709, Parent reported the following observation to the Academy: 
An elm in the Tuileries, which at the beginning of spring, 1708, had lost all 
its bark nevertheless developed its leaves, even if somewhat less vigorously, 
and kept them all summer. 

Duhamel" expresses himself as follows in this connection: Trees with 
bark wounds, which remain uncovered, gradually go to pieces (sometimes 
not until four years later). 

At the sitting of the Academy on May nth, 1852, Richard related a 
case, similar to the one described by Parent as something very extraordi- 
nary, since, in the majority of cases, the trees die soon after such injuries. 

Gaudichaud* disputes this latter statement by referring to trees in St. 
Cloud, in the Luxembourg, and at Fontainebleau, which after such injuries 
lived a great many years, although the outside of the exposed trunk was 
partially destroyed. 

At the sitting of the Academy of March 7th, 1853, the same botanist 
returns to this point and now cites the linden at Fontainebleau. According 
to Trecul, this tree was planted about 1780 and in 1810 was very irregularly 
barked by some dump carts. On the north side, the barked place was 32 
cm. long, and began 57 cm. above the ground, while on the south side it 
was 4.05 m. long and began immediately at the surface of the soil. The 
barking extended completely around the tree and yet, despite this, the tree 
lived for 44 years (it did not die until 1854). The diameter at the place 
of injury was 20 cm., below it, 18 cm. The surface of the injured trunk, 
the centre of which was so cut by the carts that the diameters of the 
remainder were 10 and 5^ cm., was entirely worm-eaten and dry. After 
the dead wood had been removed, the remaining living central portion was 



1 To characterize Trecul's theory, we will give his explanation of the figure, loc. 
cit., p. 191: A, A' bois de I'annee precedente, V, vaisseaux de ce bois; R rayons 
medullaires — B jeune bois foi-me au printemps avant la decortication. Tous les 
elements de ce jeune bois, et la partie la plus externe A' de celui de I'annSe prece- 
dente, ont subi un amincissement dans leur membrane. Les cellules externes des 
rayons medullaires R ont donne lieu Sl une multiplication utriculaire, quelquefois 
abondante en r. La multiplication commence aussi en I, V, dans les elements du 
tissue ligneux. En g, cette multiplication s'etend a toute la couche I'annee et m^me 
aux fibres ligneuses les plus externes A' de I'annee precedente. Les vaisseaux qui 
existaient primitivement dans la couche de cette annee, comme en B, v, sont 
disparu en g. 

2 Trecul, M. A., L'influence des cortications annulaires sur la vegetation des 
arbres dicotyledones. Annales di. scienc. nat., IV Serie, Vol. Ill, Botanique 1S55, 
p. 341. 

3 Physique des arbres. Vol. II, p. 46. 

4 Compt. rend, (from 31st of May, 1852). 



8o4 

found to be only 2^^ cm, thick; it was very juicy and looked like young 
wood. Almost all the root nourishment for the top of the old tree had to 
ascend this slender cylinder, and yet in the year observed, viz: March 29, 
1853, the top developed just as early and had as many leaves and blossoms 
as the other lindens. But this tree, which at its base had sent out a number 
of branches and leaved sprouts 5 to 6 cm. thick lost its foliage in August. 

Trecul ascribes to these shoots the maintenance of the basal part of the 
trunk, below the barked place ; they prepared for it the plastic material 
which a normal trunk receives from the top through the bark. 

Lindley^ describes an analogous process in a birch branch which had 
been completely robbed of bark and sapwood near the place where it joined 
the tree and yet had continued to grow for several years. 

Th. Hartig- found that a linden, from which a ring of bark had been 
removed, was still alive 9 years after the operation ; in fact, its fertility 
was increased. 

The court gardener, Reinecken, in Greiz, reports a grafted elm 10 cm. 
in thickness, which for 6 years was connected with its stock only through 
the wood and not through the bark. The Inspector of the Gardens, Roth, 
in Moscow, also found a red beech 75 cm. thick and 25 feet high, which for 
45 years had never been connected with the parent trunk by the bark (as 
Goppert states) but was connected only by the wood layers. Nevertheless, 
it grew vigorously and was finally broken off by the wind. In the botanical 
garden at Breslau, a linden 14 m. high and one-third meter thick blossomed 
every year. Its bark had been removed completely and carefully in 1870 
for a distance of one-third meter, and above the barked place, an overgrowth 
layer scarcely 2 cm. long had grown in the first 2 years^. 

The result of the barking cannot be determined in advance. The life 
duration in the barked trunk depends considerably on the variety of tree. 
Rapid growing, deciduous trees best endure such extensive injuries. Satis- 
factory results have not as yet been reported for conifers. Hartig* did not 
find any new formation of bark but discovered that the piece of the branch 
below this barked place down to the next lower branch had developed into 
very resinous wood. StolP also could find no regeneration of bark. He 
states, however, that Nordlinger had observed a new formation of bark but 
had expressed the opinion that the newly formed bark was not capable of 
conducting the descending sap current. 

Stoll states of monocotyledons that he found a cicatrization of wounded 
surfaces in a Dracaena, from which he had removed the bark. It was kept 
in a greenhouse. 

The resulting phenomena depend not only on the plant variety but also 
on the time of the manipulation and the ease with which the individual can 

1 Gardener's 'Chronicle of Nov. 13, 1852, p. 726. 

2 Hartig-, Th., Folgen der Ringelung- an einer Linde. Bot. Zeit. 1863, p. 286. 

3 Goppert, tJber das Saftsteigen in unseren Baumen. 57. Jahresber. d. Schles. 
Ges. f. vaterl. Kultur 1880, p. 293. 

* Folg-en der Ringelung an Nadelholzasten. Bot. Zeit. 1863. p. 282. 
5 tJber Ringrelung. Wiener Obst- und Gartenzeitung 1876, p. 167. 



8o5 



produce accessory organs in the form of adventitious buds and roots. In 
fruit culture, the girdling process is used only as the most extreme means 
of obtaining the setting of fruit in trees exhausted by a too vigorous forma- 
tion of w^ood. 

Personal Observations. 

To test the processes described 
by earlier observers, the bark was 
peeled from a considerable number of 
strong, about 5 year old, sweet cherry 
tree trunks in July. The upper and 
lower parts of the barked places were 
scraped for a length of 2 to 4cm. with 
a knife to destroy the sapwood ; the 
remaining part of the exposed surface 
was left untouched (see Fig. 187). 
Some of the experimental saplings 
grown on open ground were bent from 
their natural, vertical position to one 
inclined toward the ground. 

The formation of new bark did 
not take place in all specimens, but in 
a few it occurred tO' a considerable 
extent. Among the latter were found 
some small specimens which had 
formed new bark on all sides with 
the exception of the perfectly dry, 
scraped places near the upper and 
lower edges of the cut. The new bark, 
therefore, had no connection whatever 
with the old bark. The initial stages 
had appeared simultaneously on all 
sides. The thickness of the new bark, 
however, was more than twice as 
great on the lower part of the exposed 
surface as on the upper part; in fact, 
at the lower edge, it had spread in 
short bands with wartlike thickenings 
in places on the scattered scraped 
areas. In an indined trunk the con- 
tinuation of the bark had turned aw^ay from the scraped place and started to 
grow down toward the ground, as Fig. 187 e shows. 

In Fig. 187, u is the lower and u- the upper overgrowth edge of the 
peeled surface. This overgrowth edge, which in structure resembles the 
callus of the grapevine, has not been developed all around the trunk, since 




Fig-. 187. A barked trunk of a sweet 

cherry. All young- tissue has been 

removed from the upper and lower 

edg-es of the place barked. 



8o6 

a part of the bark has been left standing in the loose strips / and / . New 
wood with bark (nh) has been formed in places on these strips at a little 
distance from the place of their attachment. The real exposed surface of 
the trunk has been cut ofif from all connection with the overgrowth edges 
u,u, because at i and i' the young wood, as already mentioned, had been 
scraped off all around the trunk, in this manner forming an isolating band. 
The new formation of bark elements with the beginnings of wood had 
started on the exposed surface, cut off from all connection with the bark 
and sapwood layers. These new structures do not form a connected mantle 
but consist of isolated groups. On other, more carefully barked trunks, 



M , 




Fig. 188. 



Cross-section throug-h a newly produced tissue outgrowth on tlie exposed 
wood of the barked sweet cherry trunlv. 



the new bark extends perfectly uniformly over the bared surface. In the 
middle of this surface an irregular zone of exposed wood has remained 
without any new formation. Therefore, the new product (b) is not con- 
nected with the upper one (a), which is considerably thicker. Common to 
both and just as clearly recognizable in all new structures on other trunks 
is the thickening which increases from above downward in each individual 
tissue strip and in its appearance resembles perfectly the phenomenon 
produced by the drippings of a badly burning candle. In fact, the lower 
end of the new structure, resembling the callus, is poured in the form of 
drops over the parts of the wood which have remained naked (ee). On 



8o7 

the trunks which had been kept incHned intentionally the new structure 
hangs free from the axis, like the drippings of a slanted burning candle and, 
in response to the force of gravity, grows downward like an isolated pendent 
braid, perpendicular to the earth's surface. 

In order to show that the various small spots, as has been observed by 
Meyen, Th. Hartig and others, possibly are not merely productions of the 
medullary rays, one such structure is shown in cross section in Fig. i88, and 
in longitudinal section in Fig. 189. Fig. 188 H indicates the old wood, the 
barked surface of which {t to t) is partially dead; only the middle portion 
has started new production (N-N). 

The production began with a raising of the outermost cell layer by the 
rapidly forming products of division of the immediately underlying sap- 
wood layer and, in fact, also of the young wood cells together with the 
vessels and the medullary ray cells. 

After the cork zone (k), which is becoming thicker, has surrounded 
the comparatively scanty new parenchymatous tissue (r to p), an inner 
meristem zone appears ver}^ early at first in bands and then connected. 
This meristematic zone is new cambium (c to c), which now takes over the 
secondary growth of cork. 

In this way the two processes of growth, which can take place in the 
formation of bark on barked surfaces, differ considerably. If, as is the 
case in enclosed wounds, wdiich have been kept moist, the new bark begins 
with a great production of callus, together with a long continued division 
of the peripheral cells, as Fig. 186 shows, the formation of the outer cork 
zone and especially the production of the inner meristem zone takes place 
very late. In contrast to this, as in the present case, the wounded places 
which have been exposed unprotected to the hot summer sun show the 
second process, since the outermost remaining cells c|uickly thicken their 
outer walls, collapse and in this way furnish for the immediately underlying 
layers the necessary protection against drying. In this only a slight forma- 
tion of parenchyma, but a very rapid appearance of the cambial zone, takes 
place. It seems that the inner meristem zone has developed the more 
quickly into a callus the more rapidly a sufficient bark pressure is produced 
by suberisation. 

The next production of the new cambial regions (Fig. 188, c-c) con- 
sists in the formation of isolated new vascular bundle strands, which, 
beginning with scattered short vessels {g), rapidly increase with age the 
number and size of their elements and thus assume a wedge-like form which 
constantly narrows toward the medullary ray regions (m) and at the begin- 
ning is very broad, until structure and arrangement of the elements have 
reached the normal stage of the unbarked trunk. To each xylem part 
belongs a phloem part {ph), near which appear numerous cells containing 
calcium oxalate (0). 

We see that the appearance of the vascular bundles in the parenchy- 
matous ground tissue is the same as in the callus. This is true wherever 



8o8 



a parenchymatous ground tissue of considerable extent has been formed. 
By cross-division of a number of cells which at first do not differ in form 
from the ground mass and are but slightly elongated radially and longi- 
tudinally, a number of meristematic centres are formed from which the 
beginnings of thick-walled tissue elements start. By a very luxuriant 
callus-like cell increase from the beginning, two parallel zones of meriste- 
matic strands can be produced simultaneously, with the tissues as they 
grow older. These parallel zones mature into two wood areas, which 
remain distinct until they have become very thick. The formation of 




Fig. 189. 



Long-itudinal section through the basal part of Fig. 188, about in the zone 
to be found from g to p. 



isolated vascular bundles in the bark of our trees is not rare as is said to be 
shown in tuber-gnarls. 

The first processes of change in the sapwood of the barked cherry tree 
may be recognized in Fig. 189, which gives a longitudinal section from the 
base of the barked portion in Fig. 188. H is the old wood, which because 
of the cut has not changed any further, with its loosely reticulated vessels 
{g)\ In the sapwood, lying just outside it, the cut has so affected the 
nearly mature vessel {g) that its inner' cavity has become filled with tyloses; 
these have been used to form new cells and been changed into wood paren- 
chyma. The new layer of wood parenchyma consists of only a few cells 



8o9 

and exhibits immediately the first stages of thicker walled elements in the 
form of shorter, porous vessels (gs) as the first production of the newly 
formed cambial layer c-c. Each successive tissue layer, formed from the 
cambium, has longer vessels ; at h, we find thin-walled elements, shortened, 
to be sure, but unmistakably resembling the normal wood cells ; correspond- 
ing to these thin-walled elements, the phloem elements appear at j in the 
bark (r) : x is the xylem ray, ph the phloem ray. 

. If in the early spring, when the bark is easily loosened, homologous 
cells are torn around the whole circumference of the trunk in the process of 
removing the bark, thereby causing a reproduction of similar bark, arising 
from similar elements, we find that the bark wounds become more irregular 
from the time of the leaf development until late in June. More cell groups 
remain attached to one place on the wood cylinder than to another and the 
new structures differ accordingly. It thus happens that pieces of sapwood 
of the current year, which contain vessels, are forced up by a callus tissue 
produced beneath them. 

If the bark wounds are left uncovered, the new formation of bark will 
in many cases be more doubtful. According to my experience, the bark 
regeneration succeeds better in July, for some trees in August, than in April, 
May or June. The maple and alder must be barked earlier; numerous 
experiments made on these trees in August gave no results at all. 

If the bark wound, made in the heat of the day and left without any 
protection whatever, is investigated after some hours (sweet cherry trees 
were used for the experiment) it was found that the color of the originally 
white wood cylinder had changed to yellow. The wound surface owed this 
color especially to the browning of the medullary ray cells. 

The browning is more intense on the southwest side than on the north 
side. 

The medullary rays are easily recognized by the fact that immediately 
after the removal of the bark they project somewhat above the barked 
surface. 

This fact indicates that the medullary ray cells at the same radial dis- 
tance from the median line of the trunk have firmer walls than the young 
wood cells, i. e. their development is further advanced than that of the 
equally old cells of the vascular bundle. 

Such an advance of the medullary rays over the other tissue zvill stamp 
them as a tissue of increase, which creates space for the newly produced 
wood tissue in the direction of the radius of the trunk. 

This prominence of the medullary ray groups takes place also in part 
because of the more rapid outcurving of their outer walls, resulting, as a 
rule, from the barking. These outer walls (unprotected) grow thick very 
rapidly and turn brown. 

The cell contents increase in the medullary ray and young wood cells 
lying immediately beneath the wound surface; masses of cyptoplasm and 
later of starch appear, the former, when treated with glycerin, rounds up 



8io 

into scattered yellow globules. Beneath the outermost cell layer, which at 
once collapses and forms a protective mantle for the underlying young 
tissue, the new cell formation begins by means of cross walls. The 
medullary ray, the cells of which as a rule are in advance of the others, is 
frequently broadened by this new formation since the later ray cells push 
out in a fan over the adjoining wood cells. 

It has already been stated that often the medullary ray cells can remain 
partially or entirely undeveloped. Then the parenchymatous callus cells, 
which are never round but always polygonal, and are produced from the 
young wood fibres, spread over the medullary ray groups. As a rule, how- 
ever, the whole tissue participates equally in the formation of a thin callus 
layer which pushes out the outermost cells of the old wood. By drying 
these old cells produce a protecting layer. 

While the callus formation through the excrescent apical growth of 
the various cell rows is very considerable in the barked places, which are 
kept protected and moist, it is very small in unprotected places. Cork is 
formed at once beneath the dried, outer cell layer and becomes a constrict- 
ing, firmly protecting girdle for the underlying young tissue, which is 
turning green. 

The new formation of bark on barked places may occur in still another 
way. If the bark wound is made in such a way that young bark cells form 
the outermost layers of the exposed surface, they initiate the callus forma- 
tion and the real cambial layer is only slightly disturbed. 

The transition of the callus into normal tissue takes places in general 
in such a way that isolated, short celled, vascular strands occur deeper 
inside the callus after the cork cells have begun to form about its edge. 
About this time thick-walled, slightly porous, irregular, or polygonal cells 
are found, possibly in the same radial direction but more in the vicinity of 
the peripheral zone of the callus. These cells are the first traces of a phloem 
formation. In many trees, the first phloem elements in the form of aggre- 
gations of stone cells are found isolated or soon united into groups. In one 
zone, cells with a cloudier, denser content are found between the phloem 
and the vessel elements. In them occur a great many rectangular walled 
cells, somewhat stretched in the direction of thd long axis of the trunk, 
which might be the very first stages of the newly forming cambium. From 
this cambium are produced gradually the elongated elements which finally 
develop into normal wood and fibres but no more long, spiral elements seem 
to be formed. 

With the development of these normal fibres, the last to appear, the 
new bark may take on the function of the uninjured bark. 

The Bending of the Branches. 

Branches are often bent as a special aid in fruit culture. Experience 
shows that shoots which grow upright develop most quickly and strongly 
and that their growth in length will be the more retarded, the further the 



8ii 

branch inclines from the vertical toward the horizontal. The same retarda- 
tion of the apical growth is found, however, if branches are bent artificially 
from a natural horizontal position toward the downward perpendicular, 




Figs. 190 and 191. Artificially bent apple twig in longitudinal and in cross-section. 

from which it is evident that the bending itself exercises the arresting 
influence. 

No externally perceptible wound is produced if the manipulation is 
carefully carried out, though a somewhat greater tension may be seen on 
the upper side and a folding of the bark on the under side. 




Fig-. 192. Fold in the bark on the under side of the bend. 

The development of the buds is affected by the bending, since the buds 
below the place of bending swell up more and, not infrequently burst pre- 
maturely. The success depends upon the time and place where the branch 



8l2 



is bent. The nearer the tip of the twig the bent place Hes, the less the 
internal injury is, but also the less the desired result. The buds beneath 
the place bent will then develop into slender leaf shoots. But when the 
branch is bent near its base the buds stimulated to growth will develop only 
short shoots ; these, however, show a tendency to change to fruiting wood. 




..mk 



^£~-^T^^ ^fcg^^g^^^^|°j_^ ^(^rys;g^g~, 







Fig-. 193. Longitudinal section through the wood within the bend. 

We have spoken above of an internal injury to the axis even when 
carefully bent. This is best seen in a definite example as shown in Figs. 
190-194 of an apple branch. 

The folding of the bark is indicated in Fig. 190 (r/) and Fig. 191 (r/). 
Upon examination with the naked eye, one sees first of all a swelling of the 
wood on the under side, below a pale, brownish zone, widened at the place 
of bending (Figs. 190 and 191, hp), in the longitudinal section (Fig. 190 h) 



and in the cross section (Fig. 191 u). Except for the folding of the bark 
body no perceptible uniformly increased thickening is seen in the wood. 

In the apple branch here drawn the proportion of thickness between 
the bark on the under side and the upper side is 50 to 42, while that on the 
under side of the wood is 2 to i. The pith (m) seems in the longitudinal 
section slightly brown in stripes, especially in the lower half. Under the 
microscope many of the cells of the pith and the pith crown, often arranged 
in wavy lines, are found to have a brownish content and browned walls 
which, in various cells belonging to the under side of the pith, are sharply 
bent here and there and at these places separated from one another by 
newly produced intercellular spaces (Fig. 194). The cells show the same 
^separation even in the cross section. 

The disturbances to the bark may be recognized most easily in the 
projecting folds of the under side (Figs. 190 and 191, rf). In such folds, 
split off from the wood by the bending, the phloem bundles (Fig. 192, hb), 
as a rule, show a marked outward curving, corresponding to the peripheral 
cork layers (k) produced in considerable thickness by the squeezing of the 
epidermal cells and corresponding also , 

to the bark parenchyma (r), which 
has been broken up by numerous holes 
(/) into irregular particles. Some 
time after bending some bridges of 
radially elongated cell rows are found 
in these holes, produced by the elon- 
gation of the still elastic cells of the Fig-. 194. a pith cells which have been 
. . broken apart in the bending-; b those 

young, mner bark. which have remained uninjured. 

The apple branch in question was 
bent at the beginning of summer as is generally done in practice. The bark 
has been pushed up from the wood at the above described folds in the cam- 
bial region. The relief from bark pressure at these places has resulted in 
the formation of an abundant wood parenchyma, filled with starch, as shown 
in the longitudinal section through the wood (Fig. 193 hp). After the holes 
have been filled in and the bark pressure re-established, the wood paren- 
chyma has gradually changed into normal wood (Fig. 193 hh'). 

The filling of the holes takes place here after the coalescence of both 
parenchyma parts growing toward one another and uniting in the medial 
zone (2). This yellow colored zone, under strong magnification, resolves 
itself into a stripe of closely compressed cells. In other cases, the filling of 
the holes is produced also by new parenchymatous structures from the raised 
bark zone as well as from the remaining young sapwood tissue (as in bark 
wounds). In all cases vessels first begin to appear in the wood parenchyma 
after the holes are filled out; they gradually reach their normal length and 
development, are accompanied at first by shorter, thinner-walled wood cells, 
later by normally long and thicker-walled ones, and thus the normal wood 
formation begins. 




8i4 

After these wounds are closed, the influence of the bending is still 
always noticeable in a production of wood which takes place more vigorously 
on the under side than on the upper side. The arrangement of the newly 
formed wood (Fig. 193 h) follows, on the under side, the wavy line caused 
by the cone of parenchyma wood {hp). In contrast to the scantier, simul- 
taneously produced elements of the upper side of the bent place, the prosen- 
chyma cells of the under side are at first shorter and arranged bluntly against 
one another, with broad walls. Further, more abundantly divided wood 
cells and rows of wood parenchyma {hp'), filled with starch, are found on 
the under side between the thick-walled parenchymatous elements. 

On account of the limited space considerable parts of the tissue have 
been omitted in the drawing; also part of the normal wood, formed before 
the bending, as well as a part of the transitional tissue produced after the 
formation of the wood parenchyma and equalizing the bending. In Fig. 
193, fh indicates the spring wood of the current year, g the spiral elements 
bordering the pith (mk). In Fig. 194, a indicates the pith cells, which have 
been loosened by the bending; b, those which have remained uninjured and 
originate from the upper half of the pith body. 

If the bent twig is investigated above and below the bend, it is found 
that in the present case the influence of the bending extends on an average 
over 6 to 8 cm. 

The measurements of the branch, chosen for the drawings, are as 
follows : 

Its thickness amounted to 4.65 mm. beneath the bend, 5.50 mm. at the 
bend and 5.06 mm. above it. The bark showed toward the tip a considerable 
increase in thickness. 

The thickness of the wood, before the treatment, amounted to 

Below the bend | "PPer side 62.0 per cent. ^ 

( under side 61.9 " j of the wood cylinder existing 

at the time of the measure- 
ment, and strengthened by 
subsequent growth. 



At the bend | "PJ^^ 'if 5o.6 
( under side 35.2 

Above the bend j "PP^r side 67.4 
( under side 51.4 



J 



The increase in growth from the time of bending up to the time of 
investigation amounted to 

Autumn Wood 



Below the bend j "PJ^" side 31.0 per cent. 
( under side 31.9 

At the bend | "Pg^^ '\f 39-o 
( under side 51.8 

Above the bend j upper side 28.1 
(. under side 27.2 



Spring 


Wood 


8.0 per cent. 


6.1 




10.4 




134 




5-9 




21.9 





Therefore, the increased wood growth is comparatively greater on the 
upper side of the bend than above and below the bent place in spite of the 
great tension which may prevail on the convex side within the bend due to 



8i5 



the bending of the branch^ The loosening of the tissue, manifested at the 
bend, can no longer be recognized on the upper side. On the other hand, 
on the under side it may be traced for 6 cm. toward the tip. 

The wood cells are the widest at the bend but are wider above it than 
below it ; they seem to be wider on the under side of the branch than on the 
upper side. 

The anatomical changes vary in quantity according to the size of the 
curve, which the twig describes when bent, as well as the time of bending, 
the species and, indeed, the individuality of the branch. 

Therefore, one has in the bending of branches a simple means for mod- 
erating the grozvth in length and for directing the supply of water tozvard 
the buds which, because of their position and nature, are capable of little 
further development. 



The Twisting 
OF Branches 



d d 



i , 






a 









T r. h : A 



m n r 



^\\v vA 



^ n f! 



n n w 



h n 



Fig. 195. A branch bent with its tip downward 

and twisted at the point of bending about its 

longitudinal axis, after the coalescence of the 

inner injuries. 



The effect of twisting 
the branches is much more 
pronounced and persistent 
than that of bending, but 
follows the same general 
principles. It represents a 
further cultural method for 
the fruit grower, when he 
wishes to change the growth 
of branches. During the 
period of growth, a too lux- 
uriantly growing branch is 
first loosened in a short 
woody region by a half turn 

of the tissues about their long axis ; hereby the tissue is usually crushed and 
split longitudinally and then bent at this broken place, with the tip of the 
branch downward, so that the tip is permanently bent toward the base. Thus 
at the place of twisting the under side of the branch lies on top; the former 
upper side forms the inner side of the sharp bend, in which the wood is 
broken down to the pith. 

The most comprehensive view possible of the changes produced by 
twisting is given in the longitudinal section through the knotty, deformed 
place of twisting, which is a year old (Fig. 195). In this figure, m indicates 
the pith which has been destroyed by the breaking of the wood when 
twisted ; h is the wood of the present upper side on which a bud is seen at a. 
Because of the turning of the under side to the present upper side, the wood 

1 On the production of tension due to pressure, compare Ursprung, H., Beitrag 
zur Erklarung des exzentrischen Dickenwachstums an Krautpflanzen. Ber. d. 
Deutsch. Bot. Ges. 1906, Part 9, p. 499. Further: Biicher, H., Anatomische Veran- 
derungen bei gewaltsamer Kriimmung und geotropischer Induktion. Jahrb. f. 
Wiss. Bot. 1906, Vol. 43, p. 271. 



8i6 

has been repeatedly split longitudinally, and the "lamellae" produced by the 
tears have a spiral twist which is indicated by dd. The tears are first filled 
by parenchyma and then the cambial zone, which gradually closes together, 
deposits wavy layers of new wood (m) over the wounds below the unusually 
strained bark (r), which not infrequently splits here and there in spiral, 
longitudinal cracks. 

The original upper side, which has become the under side from twisting, 
shows still greater disturbances. The wood {h'), broken at w and partially 
split off from the pith, ends in a large knot {it) due to \tvy irregularly 
curved particles of wood parenchyma. This knot constantly increases in 
size with continued growth by the formation of new wood {n). 

It is easy to perceive that the nourishment of the tip of the branch must 
be disturbed by such an injury to the tissues and that the reserv^e substances, 
visible as starch in the parenchymatous overgrowth parts of the edges of the 
wound, must be enough for the use of the immediately adjacent buds. From 
what has already been said, it is evident, likewise, that besides this increase 
in nourishment the buds found directly beneath the place of twisting will 
also profit from the increased water pressure. 

The treatment of twisting, as already remarked, is an effective means 
of retarding the apical growth of a branch to the advantage of the basal buds 
■v. it.:ont, however, causing the uppermost lateral buds, lying below the injury, 
to sprout at once. The lateral bud immediately below the place of twisting, 
grows out to a new, vigorous leafy shoot only when the injury to the tissues 
in the twisting has been so great that the leader can no longer receive the 
amount of water most necessary to replace that lost by evaporation. It, 
therefore, dries quickly especially if the maniplation is carried out too early 
in the year. This result is naturally not desired by the grower. A twisting, 
carried out too late in the year, would not produce an effect sufficient to 
prepare the basal buds for fruiting buds, but still would arrest the growth of 
the branch in length and cause a better ripening of the wood so that it will 
better withstand the winter. 

In the propagation of quinces by layering, the branch, which is to be 
layered, is twisted once about its long axis at the place where it is to form 
roots in the soil. This kind of disturbance is similar to that in the above- 
mentioned case; the result different inasmuch as the retarded, descending 
plastic material is used chiefly for the formation of adventitious roots. 

German grape growers in the vicinity of Tiflis are said to tmist the 
stems of the ripe clusters and, thereby, obtain a better wine. The changes, 
initiated by this treatment, dovetail into one another as follows : the supply 
of water, from, the vine to the cluster, is lessened by the twisting of the 
stem. Consequently, the evaporation greatly exceeds the supply and the 
juice of the berries becomes more concentrated. Whatever starch happens 
to be in the stem is carried as sugar to the berries. They break up and utilize, 
thereby, a part of the organic acids. The same processes occur in the 
ripening of cut grapes. 



8i7 

The Effect of Constricting the Axis. 

The "Constriction" consists in the close binding of an inelastic band 
(i, e. string, wire, etc.) about a trunk or branch. The results of this treat- 
ment show, to the casual observer, that this constriction of the axis is 
nothing but a local, artificial increase of the sap pressure. But here the 
most extreme case of sap pressure takes effect at once, since the formation 
of new structures below the constricting place are gradually reduced to a 
minimum and finally disappear entirely. The xylem elements, near the con- 
stricting band, thus deviate from their perpendicular course, even increasing 
their inclination to the horizontal, so that I think in the different normal 
trees themselves the more or less spiral twisting of the wood fibres is con- 
nected with the greater or lesser pressure exerted by the sap. 

Finally, the tree becomes so thick above the constricted place that the 
bark splits above the band and later also below it. This removes the sap 
pressure almost entirely. The result is a luxuriant formation of wood 
parenchyma which, with the aging of the plant part, passes over gradually 
in the later annual layers into normal wood and overgrows completely the 
band or the wire. Such an overgrown constriction bears great outward 
resemblance to a grafted place but has naturally no internal structural resem- 
blance to it. 

In Fig. 196 (see page 819) two dift'erent stages of the constriction are 
shown. Fig. 196, i is a year old maple branch, with a constricted place 
only a few months old. Fig. 196, 2 is an older branch, which shows the 
overgrowth of a wire ring, several years old. Fig. 196, 5 is a longitudinal 
section of Fig. 196, 2, where d and d' represent the cross sections of the wire 
ring ; u represents the overgrowth edge, which is more greatly developed on 
one side (u) by the increased supply of nutritive substances from the branch 
(z) above it. Here it has overgrown the wire earlier than on the opposite 
side. 

An anatomical investigation of the stage represented in Fig. 196, i 
shows that the constriction at first cannot produce very extensive changes. 
The bark has suffered the greatest disadvantage and it is chiefly the cell 
layers, lying on the outer side of the primary bark, between the phloem 
fibres, or between the stone cell aggregations and the epidermal cells, which 
have been especially compressed. The cell layers next the phloem fibres 
seem to be the most pressed together ; the effect is less marked on the next 
layers toward the outside, which are often thickened like collencliyma. 
Their cells are compressed to ^ or ^ their normal diameter and it would 
seem as if they hereby become somewhat longer than the corresponding 
cells in an unconstricted place. The sub-epidermal, almost square cells, are 
compressed to half their diameter. The epidermis suffers least of all. 

If, as in Fig. 196, i, the constricting band is wound several times about 
the branch, apparently very prominent callus rolls become noticeable 
between every two turns. In them the aforesaid parts of the bark are devel- 



oped in a way exactly the reverse of that at the constricted place. The cells, 
bounding the phloem fibres, which in the normal branch are elongated, 
become considerably broader radially; in fact, they appear like long 
cylinders, lying perpendicular to the phloem fibres; thereby, the overlying 
bark tissue, which participates less in the radial elongation, is pushed out- 
ward. Moreover, the rolls, lying between the two constricted places, are 
not absolutely large; they are relatively conspicuous only in contrast to the 
depressions. The secondary bark and the wood follow the convexities and 
concavities of the primary bark even if with far smaller variations. The 
pressure, which makes itself felt in the tissues, acts not only where the band 
lies on the bark but also somewhat above and below the actual place of 
constriction; this is seen especially in the cross section of the cells. The 
mutual proportion in the mean of measurements is : 

In the Bark 

Normal Roll Constricted 

Fig. 196, I n Fig. 196, / w Fig. 196, i g 

11,2 11,8 9,4 

In the Wood 
7.3 6,9 4,6 

Therefore, according to these mean figures which, moreover, show con- 
siderable fluctuation, an increase manifests itself only in the round and 
apparently broader cortical cells ; the wood cells, on the contrary, seem some- 
what narrower than those of the normal wood but it should be emphasized 
that the same maximum diameter of the wood cells has been found in the 
roll as in the normal part of the branch at some distance from the constricted 
place and only the frequency of the occurrence gives the decision. 

If the constriction becom,es older, without the band being broken or 
loosened, as was the case with the wire band shown in Fig. 196, 2 and 5, 
then the pressure of the wire on the layers of the bark finally increases 
because of the growth in thickness of the underlying wood in such a way 
that the bark layers are killed and changed into a brown crumbling mass. 
Finally, the healthy bark splits above and below the wire and inclosure of 
the wire begins. Because the overgrowing layers of the annual ring are 
considerably thicker in wood and bark than at places at some distance from 
the wire, the former constricted place finally projects in a considerable roll. 

Fig. 196, 4 shows the section, indicated in Fig. 196, 5 at a, considerably 
magnified. We see here in longitudinal section a little of the old wood of a 
branch (//) before the wire {d) was bound about it and perceive the new 
structures of the overgrowth edge at first in the immediate vicinity ( U) of 
the wire and then a continuation of these tissues from the older annual layer 
([/'). The transitional stages have been omitted for lack of space, likewise 
the representation of the coalescence, extending about U', of the very 
uppermost overgrowth edge with the under one and the representation of 
the transition from the irregularly running wood elements of the overgrowth 



H' 



,fvffi'le^!^!!J^^l'*'v'-' 






u' 



h'- 



\ ^-'-\ 






!<:'„ 



Ft^.4 



M^f '^ '^-)~' 



^^. 



h/t '\ 







"^ e-S'^' — > 



)Jr 



/^ 






■^ 



-A" 




^^^>^? 







Ti^7 




Fig. 3. 






Jf 



1 







.'c: « 




Fig-. 196. I is a consti'icted one year old bi'anch; 2, a branch several years old which 

has overgrown the wire ring-; 3, longitudinal section through Fig. 2; 4, anatomical 

aketch ot a longitudinal section from a zone originating at a in Fig. 3. 



820 

edge to the normal wood structure, as it gradually forms in the later annual 
layers above the place where the wire is. 

If the wood had grown normally, without the arrestment of the wire, 
its structure would have necessarily remained the same as before it was 
constricted, as represented at H ; wood cells {h) with vessels {g) would 
have been formed in regular succession and this broad wood would have 
been uniformly divided by radially extending medullary rays (w). Instead 
of this, we find the constricted place and above it {h',h) a kind of wood 
produced by the effect of the wire composed almost entirely of wood cells 
without vessels. Only in the beginning are these wood fibres deposited at h' 
exactly parallel with the long axis of the branch; the more they are found 
in the direction {h' ,h" ') the more diagonally they run and the more twisted 
they seem. The wood formed after the wire has been bound on has, there- 
fore, become denser, poorer in vessels and more twisted. The medullary 
rays, which otherwise run as straight radial bands from the pith toward the 
I crk, are as twisted and outspread toward the top as the wood cells, so that a 
section made exactly in the direction of the radius intersects several of the 
curved rays (m"). 

The difference between the wood cells and medullary ray cells is not 
noticed until at some distance from the wire. In the immediate vicinity of 
this we find an almost uniform parenchymatous wood {hp), of which the 
edge is dead and black and represents the dark line which may be seen in 
Fig. 196, J, extending upward a little distance from the wire {d'). The 
black furrow no longer extends entirely to the outside, since the later 
annual layers (Fig. 196, 5,w') have already united with one another. These 
overgrowth edges, united with one another to form a common, connected 
wood layer, are indicated in Fig. 196, 4, by the tissue H.' Here we find the 
ducts {g') and the wood cells {nh') formed as in normal wood (only 
shorter) but their course is horizontal instead of vertical in the plane lying 
at the same height as the wire. Only at some distance from the actual place 
of constriction upward or downward do these elements begin to pass over 
gradually into their normal perpendicular course (Fig. 196, 4 g'h'). The 
browned, or blackened, zone {hp) is not continued to U'. 

The term "browned" or "blackened" has not been chosen without good 
reason, for the color from t to t' is as black as ink, from there toward /" a 
brownish black. In fact, it is ink which colors the clotted cell contents near 
the wire. The tannic acid of the tissue has combined with the iron of the 
wire and, therefore, killed the cell contents in the immediate vicinity. 

This compound is diffused for considerable distances and, in fact, 
farther into the old wood through the medullary ray tissue than transversely 
through the wood cells. The fact that the wire lies directly against the old 
wood and has killed a zone of it should not be surprising, when we think 
that the constantly increasing pressure of the distending branch against the 
inflexible wire, leads to the compression of the soft bark and the cambium 



821 

and kills them. The dead tissue can be recognized only in small fragments 
along the wire. 

We have already explained above how these different tissue forms are 
produced by the sap pressure, at first greatly increased and then nearly 
removed by the splitting of the bark around the wire. The almost complete 
breaking up of the split bark makes possible the appearance of wood paren- 
chyma from the cambial zone; later, if sap pressure begins because of the 
uniting of the wound edges over the wire, thus enclosing it, true wood cells 
and vessels again appear but the arrangement of these elements for some 
time is horizontal, or spiral, diagonally ascending, caused by the strong 
pressure of the wire at the time when the cambial zone still lay back of it. 

The extreme twisting of the wood fibres, which can be confirmed also, 
to a slighter extent normally, in a great many trees, and manifests itself in 
different degrees in individuals of the same species, is physiologically inter- 
esting. The tivisted growth is more noticeable in dry places. The greater 
twisting of the wood fibres, probably caused by the bark of specimens grown 
in dry places which becomes inelastic sooner, is less easily split and, there- 
fore, exercises a higher pressure. 

The practical purpose of constriction is the same as that of girdling but 
without the danger entailed by a complete removal of considerable parts of 
the bark. 

Branch Cuttings. 

The term cutting is applied to any part cut from the parent plant, which 
by its resen-e food materials incites various cell groups, chiefly those near 
the cut surface, to renewed vegetative increase so that a cicatrization tissue 
is formed. The separated part by forming new roots develops into an inde- 
pendent plant. A work by Simon^ throws hght on the anatomical conditions 
and the dependence of tissue differention on external factors, which appear 
during the pressure and can not longer be taken into consideration. 

It may be asserted that an asexual propagation of this kind may be 
found in all classes of the vegetable kingdom and may take place from very 
different organs. We recall here the continued growth of torn off mycelial 
threads, of cut sclerotia, of isolated fruiting stems of the frondiferous 
mosses and of leaf and blossom parts of phanerogams. Beside the fre- 
quently occurring root cuttings, cases have also been known of the formation 
of roots from fruits. 

We are concerned here for the present with cuttings from branches, 
the cut surfaces of which react to the w^ound stimulus by the formation of 
callus. In connection with this, we will then discuss propagation by root 
cuttings, the cicatrization of which also begins with the formation of callus. 
The transformation of the callus into an actual overgrowth edge by the 
formation of a peripheral cork zone bears very" great resemblance to the 
formation of the overgrowth edges on girdled, or transversely cut, woody 

1 Simon, S., Experimentelle Untersuchung-en iiber die Differenzierungsvorgang-e 
im Callusgewebe von Holzgewaclisen. Leipzig- 1908, Gebr. Borntrager. 



822 

branches. But in cuttings the moist medium, in which the cut surface is 
placed, acts as a modifier. A difference should also be determined accord- 
ing to whether the branch furnishing the cutting was already in a woody 
condition, or was still herbaceous. Instead of extensive analyses, we will 
give here illustrations of an herbaceous Fuchsia cutting and a woody rose 
cutting. 

The basal part of the Fuchsia cutting (Fig. 197) is shown in longi- 
tudinal section ; j to j indicates the original cut surface ; the elements appear- 
ing below this line were formed after the cutting was made ; above it {s to s) 
lie the original tissues, only one-half of which have been shown, ni is the 










11 ^fv^m.,^ 







Fig. 197. Fuchsia cutting. 



pith ; h, the wood, r, the bark, in which extend the phloem fibres {h). These 
as well as a part of the wood cells {K) have browned on the cut surface and 
died. The outer bark (r) also has dried up in the region of the cut surface. 
The younger, inner bark layers, on the contrary, and especially the pith, 
have healed over the wound surface by an abundant cell increase. The 
outer part of this cicatrization tissue is turned to cork and this cork layer 
{k) has grown to a considerable size through the activity of the cork cam- 
bium {ke), which forms the protection for the more tender, inner bark 
tissue. In the callus bark we find the broadened pouch cells (0), with 
calcium oxalate in raphides. Near these are isolated cell groups, with 
thicker walls {h'), which represent the phloem of the vascular bundles 



823 

already formed in the callus, their wood being suggested by strands of short, 
reticulated vessels (g"). These adjoin the vessels in the wood of the cut- 
ting, the thin-walled wood cells of which, rich in starch and bounding the 
pith, have participated in the formation of callus. The old wood of the 
cutting was torn when cut. The torn place (d) is filled with callus and the 
cambial zone {c to c) may be traced even into this torn place; it passes 
through the callus in a connected curve. The normal cambium of the cut- 
ting lay on the outer side of the wood (h). By cutting off the branch in 
making the cutting exactly the same change has taken place as in the ringed 



«.' 




Fig'. 198. Rose cutting. 



branch. At first uniform parenchymatous tissue was formed from the 
cambium, in which short, reticulated vessels (g) gradually appear. Toward 
the cut surface these tissue parts have become bounded by a heavy cork 
layer (k'), but in the outermost bark cells increase has also taken place and 
in the new tissue a formation of short vascular cells (g) on the outer side 
of which is recognizable a meristematic layer (c'). 

In the present example the pith, as well as the cambium, has been the 
chief centre of callus formation. 

On the other hand, the pith has remained quite inactive in the case of 
the rose cutting (Fig. 198). 



824 

Here too j to j indicates the line of the cut; all below this is callus 
formation, which has pushed out the thick rolls from the original cambium 
and spread over the cut surface from its outer edge inward. In the longi- 
tudinal section shown in the figure, we distinguish a roll (ca) cut through 
radially and a callus (ca-), projecting outward from the back edge and then 
cut across, the bark of which has already united with the laterally incurving 
ca. Thus, in this older rose cutting at any rate the pith is covered but this 
takes place by the union of edges, curving in from the periphery toward the 
centre, while in the Fuchsia cutting illustrated above the main mass of callus 
is formed by the pith itself. 

The indication of the various elements agrees in general with that of 
the preceding drawing, m is the pith, which was here torn when cut. The 
cut (li) has been filled with callus projecting out from the back edge; h is 
the old wood, formed before the branch was cut off; nh, the new wood 
formed during the period of propagation, exactly corresponding in character 
to the new wood of the callus in the grapevine. This begins with short, 
wide, porous, thick-walled cell masses, rich in starch, in which occur like- 
wise short reticulated vessels. Their elements become narrower and nar- 
rower toward the outside and more elongated, more and more resembUng 
the normal ones the later they are formed after the cut is made, i. e. the 
closer they lie to the cambial zone cc. This cambial zone extends around 
the cut surface of the old wood in broad curves and is covered on the outside 
by the newly formed bark (nr) which is not completely reproduced in the 
drawing. We notice on the outermost edge of the bark the corked and 
dying first stages of callus (a), extending at first over the cut surface and 
formed of broad, spherical to pear-shaped cells, arranged in rows, the end 
cells of which are rounded. These cell rows are increased at first at the 
ends, since the outermost cells have enlarged and been divided by cross walls, 
and the small end cells thus reduced in size repeat the process when growing 
further. 

In the callus roll (ca-), which extends from the back outward, and has 
been cut transversely, g indicates the short reticulated vessels, which repre- 
sent the beginnings of the new wood. Around this extends the cambial zone 
(c'). b is the old phloem strand, formed before the cutting was made. It 
has been pressed far away from the old wood at the cut surface by the 
abnormal new wood formation, and has died at its free end. The cells lying 
against both sides of the phloem fibre groups have been released from the 
sap pressure by the cut and have stretched transversely (/), while in 51 
normal condition they would be elongated. The remaining outer part of 
the old bark (r) has not changed and has closed the wound with cork. 
indicates the rhomboid, isolated crystals and stellate druses of calcium 
oxalate. 

The new roots grow sometimes from the callus itself, sometimes from 
the basal regions of the cutting above the callus, according to the plant 
species. 



825 

The Utilization of the Various Axial Organs for Cuttings. 

Callus formation itself as we see is, therefore, the simple process of 
healing a transverse wound. The formation of the cicatrization tissue at 
the base of the cutting is aided by especially favorable conditions. Except 
in healing the upper edge of the wound, the reserve substances in the cutting 
momentarily find no other use than in the cicatrization of the lower wound 
surface, since the usually shady place of propagation does not favor the 
bursting of the buds. Where the growing conditions given the cuttings 
through ignorance cause a rapid development of the buds, the formation of 
callus and roots is reduced or fails entirely. In the second place, the moist 
place of growth and the usually increased temperature of the soil act in 
such a way that cell increase is favored on the lower cut surface, i. e. the 
cicatrization tissue assumes a very luxuriant character. The formation of 
callus is not absolutely necessary for the cutting. Plants, which very easily 
produce adventitious buds, reduce their callus tissues to very small amounts. 
They cover their cut surface by a formation of cork and utilize their reserve 
substances at once for the formation and further development of new root 
primordia. Here an abundant cell increase occurs only in the cambial zone, 
lying immediately in the cut surface, whereby the base of the cutting 
enlarges considerably (Begonia). The formation of callus can become very 
injurious in trees which form, adventitious roots with difficulty, since by its 
especially abundant development it consumes the material provided for the 
formation of new roots. We find, at times, enormous knotty callus swell- 
ings without any formation of roots (conifers). 

The kind and age of the cutting and the vegetative conditions given it 
determine which tissue shall participate in the callus formation. The 
cambium always takes part in this. Where it does not assume exclusively 
the process of healing, it is assisted by the parenchyma of the inner bark, or 
also by a part of all of the parenchyma of the pith. Further, even the 
parenchyma of the wood and that of the older bark can participate in this. 
In herbaceous, rapidly growing plants, even in their thick-walled elements, 
a cell increase occurs near the cut surface because of the formation of 
tyloses in the vessels and of a new formation of cross walls in the collen- 
chyma of the older bark. It has been observed here ^ that the thickened 
walls of the coUenchyma cells and the vessels in the immediate proximity 
of the tyloses swell up, become porous, and are, in part, re-absorbed. 

The more living parenchyma therein present, the more rapid and 
abundant is the callus formation. The cuttings are generally made at a 
node directly beneath a bud. In a cross section through a bud-cushion it is 
found that the parenchyma mass is greatly developed here by the passing 
over of the medullary connections into the bud. At the node the pith 



1 H. Criig-er on Trinidad; Westindische Fragrnente, XII. Einig-es iiber die 
Gewebesveranderungen bei der Fortpflanzung- durch Stecklinge bei Portulaca oler- 
acaea. Bot. Zeit. 1860, p. 371. 



826 

parenchyma, as a whole, is usually livhig and capable of dividing, while it 
has died in the remaining part of the branch and is partially torn. 

It should be remarked, however, that no constant rules may be given 
for the kind of callus formation. Often, especially in herbaceous plants, 
the cuttings form only very little if any callus on the wound surface, swell- 
ing out and being cut off by cork, but in another case the plants furnish 
considerable masses of callus. The perfectly herbaceous summer cuttings 
of Vitis, especially the American varieties, usually develop but little callus ; 
sometimes, however, great masses of it. The same is true for rose cuttings, 
if they are cut in the early spring in a vegetative soft condition, from forced 
plants and stuck in a warm sand bed. A large supply of food and its slow 
utilization awaken a tendency to callus excrescence. 

A work by J. Hanstein\ provided with a detailed' bibliography, takes up 
girdled cuttings. He found that such cuttings, with isolated wood and bark, 
w^hich had been girdled near the base, developed roots above the girdled 
surface and not on the under cut surface. If cuttings, which had already 
formed roots, were girdled, the further development of these roots ceased 
and a new formation began directly above the girdled surface. An excep- 
tion to this rule is found in all those plants in which fully developed vascular 
bundles are found or, at least, a fully developed, sieve tube system in the 
pith. In them despite the girdling roots are found on the under cut surface 
of the cutting. When stating these results, we need only add that the oper- 
ation must be carried out with ripe, or nearly ripened axes in order to obtain 
these results. If very young herbaceous tips of woody plants are used, in 
which also the girdling can be done cleanly only with difficulty, the new root 
system is produced on the cut surface, or in its immediate vicinity. In this 
all the tissues with the exception of the old prosenchyma elements participate 
in the callus formation. The part above the girdled surface then frequently 
dries up. The same phenomenon may be observed if cuttings are placed 
upside down in the earth. Only infrequently do such cuttings grow further. 
After they have formed callus and even roots on the end standing in the soil, 
which is organically the upper end, they usually die back from above down- 
ward to a small basal part and then develop new shoots from this. 

The results are of practical importance inasmuch as they clearly illus- 
trate the transference of the plastic material, necessary for all new structure 
formation. We see that the main paths for the building materials should 
be sought in the sieve tube system in the bark. If such paths exist also in 
the pith, a transference of the plastic substance likewise takes place there. 
Besides these main paths there are also in cases of necessity side paths, which 
become of importance. The parenchyma cells of the bark and pith will also 
conduct the plastic materials upward and downward and likewise, as we see 
in the new formation of bark on bark wounds, the medullary ray cells in the 
axis can radially transport dissolved, reserve substances ; but the quantity 



1 Hanstein, Johannes, tJber die Leitungr des Saftes durcli die Rinde. Pring- 
sheiin's Jahrbiicher fiir wissensch. Botanik, Vol. II, 1860, p. 392-467. 



827 

fransported in this way is small and, therefore, insufficient for any new 
structures worth mentioning. The plastic substances are carried much 
more poorly organically upward, i. e. toward the tip, than organically 
downward. 

As we see from cuttings set upsidedown and can perceive also from 
intentionally reversed grafts, under favorable conditions a transference of 
all fluid materials in the plants, the raw soil solutions as well as the plastic, 
organized constructive substances, is possible in all directions. The most 
easily passable paths are naturally used first ; when any hindrance occurs 
there the side paths become of increased importance. In cuttings callus can 
be formed on every wounded place and this callus can produce axes con- 
taining chlorophyll and roots. Whether such a case will actually occur 
depends on external conditions and the typical developmental law peculiar 
to each plant, changed only with difficulty. Many plants form adventitious 
roots from the internode so rapidly that the callus formation on the cut 
surface has not sufficient time to make any development worth mentioning. 

Contradictions in the results of the various observers are explained by 
the diversity of the external influences. Thus Stoll^ states that no callus 
became visible with Pogostemon Patchouli, while Hansen- observed it. The 
former found no new vegetative points were developed from the callus 
tissue, while the latter could prove them, etc. 

In practice it is advisable in propagating bushes not to make cuttings 
from, ripened, old wood but from succulent shoots, which when possible are 
taken from plants forced in the winter in greenhouses. Under certain con- 
ditions it is advisable to make cuttings also from plants, which as a rule are 
propagated from seeds. It is a well known fact that cucumber and melon 
plants from seed of the previous year make very luxuriant foliage growth 
but set fruit less abundantly. Old seed with contents poor in water, how- 
ever, like wilted seed potatoes and the like, behaves more favorably since 
the vegetative activity of the plant appears to be modified. Cuttings from 
the tips of vigorous shoots of cucumber and melon plants, forced in the hot 
bed and bearing the first fruit possibly in May, give within a few days and 
about this time well rooted plants with greater fertility than plants from seed. 

Here, at the end of the chapter, it is necessary to call attention to the 
fact, that propagation by cuttings is often used for the development of new 
varieties. Many teratological and pathological conditions, which appear 
temporary in different parts of the plant, become fixed in the cutting. A 
great many plants with highly variegated foliage, varieties with double 
blossoms, etc., which originally appeared on isolated shoots, have been made 
permanent by cuttings. Temporary juvenile stages in Conifers varying 
with the place of growth are propagated further by cuttings and offered for 
sale as new forms or varieties. A few striking examples of this kind form 



1 Tiber die Bildung- des Callus bei Steckling-en. Bot. Zeit. 1874, Nos. 46 and 47. 

2 Hansen, Ad., tJber Adventivbildungen. Sitzung'sber. d. phys.-med. Sozietat 
zu Erlang-en June 14, 1880. 



828 

valuable suggestions for further experiments along this line. According to 
Beissner^ in order to obtain Chamaecyparis squarrosa from cuttings of 
Biota orientalis only the small branch axes with decussate leaves should be 
used, which are found close above the cotyledons. The majority of these 
little branches always give Biota meldensis, but with an evident scale-like 
position of the leaves, Biota orientalis. Likewise, cuttings of the first shoots 
of Callitris quadrivalvis give a new form. The fixed juvenile stage of 
Cupressus sempervircns may be seen in C. Bregeoni; the first shoots of 
C. Lawsoni give a form with squarrous leaves. Retinospora ericoides,, 
Zucc. was obtained from Chamaecyparis sphaeroidea var. Andalyensis. 

The diversity of plants obtained from the ivy according to whether the 
cutting is taken from blind or blossoming wood is well known. 

Aside from the often simpler leaf form of blossoming wood, which is 
easily transmitted to plants from cuttings, we often find their habit of 
growth to be more dwarfy and bushy. The subject of the retention of 
juvenile forms has recently been treated thoroughly by Diels". 

Propagation by root cuttings is still but little used, although very advan- 
tageously in many woody plants. Paulownia, Ailanthus, Syringa, Aralia, 
Mespilus, Rosa, Malus may be propagated by removing larger root branches 
before the first growth in the spring, or before the second growth in July. 
These are cut into pieces possibly 5 cm. long and laid flat in rows in the soil; 
New plants rapidly becoming independent by their own root formation are 
produced at different places in the piece of root by adventitious bud forma- 
tion. Among the conifers, Araucaria, Podocarpus and Gingko are said to 
be advantageously propagated by root cuttings especially if these are set in 
a warm bed. Large root stocks survive splitting lengthwise; each half then 
develops adventitious buds. 

Some plants may also be propagated by bud cuttings (Vitis, Paeonia 
arborea). The buds are cut from the old wood in the spring just as if one 
were cutting long buds with some wood for grafting and these hud cuttings 
are laid flat on the surface of the soil in pots. It is advisable, however, to 
excite rapid growth by warming the soil. 

We can also speak of tuber cuttings, since there exists a method of 
propagating plants by boring the eyes out of the fleshy tubers with a part 
of the tuber tissue containing reserve substances (potatoes, caladiums). 
Usually the part of the tuber, which has been cut out, forms cork on its 
exposed wound surface at the expense of the starch and retains the remain- 
ing reserve substances for the first nutrition of the eyes, which become 
independent quickly by the development of adventitious roots. The cutting 
of seed potatoes should be discussed in this connection. In practice the 
precaution is observed, as a rule, of not placing the pieces of tubers in the 
soil immediately after cutting. This precaution is perfectly justified, since, 

1 Beissner, tJber Formveranderung- von Koniferensamlingen. Regel's Garten- 
flora 1879, p. 172, cit. Bot. Jahresber. 1879, II, p. 2. 

- Diels, L., Jug-endformen und Bliitenreife im Pflanzenreich. Berlin 1906, Gebr. 
Borntrag^er. 



829 

in planting freshly cut pieces, a decay easily occurs among them as soon as 
even a little moisture is present in heavy soils. If on the contrary the cut 
pieces are left a few days in the air, cork layers are formed under the cut 
surface, which protect the pieces of tuber. If the tubers are cut too early 
before sprouting, it may happen in some varieties that the pieces remain for 
some time in the soil apparently unchanged without any sprouting of the 
eyes. It is, therefore, advisable with tender varieties to spread the tubers 
before planting in a light, warm place until the eyes begin to enlarge and 
then to undertake the cutting. 

The importance of the cork formation on the cut surface is shown by 
an experiment made by AppeF, who supplemented the results of studies by 
Kny- and Olufsen^. While the two last named investigators perceived the 
tuber's chief protection against infection by parasites to be the wound 
periderm forming beneath the cut surface after a short time, Appel proves 
that the potato is able to protect itself before the wound cork is produced. 
He finds that in the most favorable cases the periderm formation sets in 
only on the third day after the injury and ends after two days more. There- 
fore, the wounded place would lie unprotected for that length of time 
against the demonstrably rapidly penetrating bacteria of decay if the walls 
of the undestroyed cells lying directly beneath the wound surface did not 
turn to cork immediately on the side toward that surface. In fact, this cork 
deposition completed after twelve hours was found in a part of the cell wall 
of the first and second cell layers beneath the wound surface to be entirely 
sufficient to prevent infection from Bacillus phytophthorus. The process 
of suberization develops less well if the pieces of tuber dry at once and are 
kept warm (for example, within doors). The outermost cell layers of the 
cut surface then dry up so quickly that the two factors necessary for the 
turning to cork, viz : oxygen and moisture, have only insufficient access to 
the tissue layers under consideration. 

The closing of wounds in all fleshy parts of plants takes place in the 
same, or a similar manner*. 

Grafting. 

Improving the stock by grafting consists in the artificial removal of one 
or more buds and their insertion in a living part of a plant for the sake of 
further nutrition and development. The inserted parts are usually held 
fast by a bandage and protected by grafting wax from the injurious effects 
of the atmospheric conditions. The inserted part can in general be called 
the "scion," while the nourishing trunk is called the "stock." The newly 
produced tissue furnished in part by the stock and in part by the scion, 



1 Appel, Otto, Zur Kenntnis des Wundverschlusses bei den Kartoffeln. Ber. d. 
Deutsch. Bot. Ges. 1906, p. 118. 

2 Kny, L., tJber die Bildung- des Wundperiderms am Knollen in ihrer Abhan- 
giglceit von ausseren Einfliissen. Ber. d. Deutsch. Bot. Ges. 1899, p. 1.54. 

3 Olufsen, Untersuchung-en iiber Wvmdperidennbildung an Kartoffelknollen. 
Bot. Centralbl. Supplement, Vol. XV, 1903, p. 269. 

* Kiister, Ernst, I'atholog'ische Pflanzenanatomie. Jena 1903, G. Fisher, p. 185 ff. 



830 

which unites the two artifically connected members, is called the "connecting 
layer," or, according to Goppert, "intermediary tissue." The scion is either 
a single bud, which has been separated, together with a part of the adjacent 
bark, or a piece of a twig with several buds. According to the cultural 
purpose the scion can be inserted at the place of its removal, or at some 
other place in the same individual or (most frequently) on some other indi- 
vidual. In the first phase, only the effect of the injury; in the latter, in 
addition the influence of the difference in character of the scion and the 
stock will have to be considered. 

This process of improving the "stock" will have to be considered first 
of all as a process of wound healing; the favoring, or arresting influence, 
will have to be taken into account secondarily, due possibly to the mutual 
interaction of the two artificially connected plant parts. 

Among the authors treating this subject thoroughly, Goppert^ should 
be named first of all. He took up the subject especially through anatomical 
studies. A year after the publication of Goppert's well illustrated work I 
published a supplementary article, in part confirming it and in part correct- 
ing it". Among the earlier physiologists, the statements of Hanstein^, of 
de Candolle*, of Treviranus^ are especially worthy of consideration. 
Thouin*' made a systematic compilation of all the possible variations in the 
process of grafting. He based his work on DuhameF, La Quintinye^ 
"Rozier^, Cabanis^" and the other horticultural writers and by means of 
abundant bibliographical citations facilitated tremendously the study of the 
history of the art of grafting. 

Of the various forms of grafting which Thouin describes in his book 
under separate names and usually illustrated, only a very few have found a 
general acceptance. All the forms in use at present will from a pathological 
point of view be best arranged in their respective values, according to the 
degrees of injury which the stock suffers and according to the greater or 
lesser degree of ease with which the wounds can be healed. Under other- 
wise similar circumstances, the success of the manipulation will be the more 
certain the more rapidly the tissue of the scion forms a firm connection with 
the stock and, since this connection is brought about by means of the newly 
produced cicatrization tissue of the wound, the rapidity with which the 
wound is closed becomes the standard, chiefly, if not exclusively, for judging 
the value of the form of grafting. 



1 Goppert, tjber innere Vorg-ange bei dem Veredeln der Baume und Striiucher. 
Kassel 1874. 

2 Sorauer, Vorlaufige Notiz iiber Veredlung. Bot. Zeit. 1875, p. 201. 

3 Hanstein, Dr. J., Das Reproduktionsvermogen der Pflanzen in Bezug auf 
ihre VeiTnehrung und Veredlung. Wiegandt's Volks-und Gartenkalendar 1865, 
p. 190. 

4 De Candolle, Physiologie vegetale II. 

5 Treviranus, Physiologie der Gewachse 1838, 11, p. 647. 

6 Thouin, Monographie des Pfropfens. Berg's translation, 1824. 

7 Duhamel, Physique des arbres 1758, II, p. 75. 

8 De la Quintinye, Le parfait jardinier. Paris 1695. 

9 Rozier, Cours complet d'Agriculture, Vol. V, p. 346. 
10 Cabanis, Principes de la Greffie, p. 105. 



- 831 

The phenomena of union possible in grafting may be traced to the 
healing processes of three classes of wounds which I have called bark 
wounds, surface wounds and cleft wounds. 

The injuries termed bark wounds (as evident from the earlier chapters) 
are those produced by a complete removal of the bark, so that the wood is 
exposed without, however, losing any of its parts. The form of grafting 
in which this peeling process forms the main part of the injury belongs to 
the type of budding. Here, at the time of the greatest cambial activity, the 
bark is raised for a certain distance from the wood of the stock and the 
scion (bud) is inserted into the exposed place. This scion consists of a 
single eye with a small bark shield {budding with bark), or of an eye which 
has been cut out with some wood from the parent branch (budding with 
zvood) or of a piece of an entire twig which can be inserted in different 
ways and is shoved under the bark of the stock with its cut surface against 
the wood cylinder (bark grafting). 

Under the term "surface wound" are included all the injuries in which 
a piece of the wood is taken away together with a complete removal of a 
part of the bark. The surface wound looks and behaves differently, accord- 
ing to whether this wound surface is produced by a longitudinal or a cross- 
cut. If the piece is cut from the axis longitudinally, the elements of the 
bark and wood are exposed lengthwise. The rain water runs off easily 
from this surface wound, while in a cut across the trunk it collects in little 
troughs and can much more easily cause the decay of the wood, A hori- 
zontal surface wound is always much more dangerous for the axis than one 
running vertically. On this account in general practice diagonal cuts are 
usually made, instead of horizontal ones. 

The kinds of grafting, in which surface wounds come into play chiefly, 
or exclusively, belong to the type of "Copulation." The simplest form of 
this consists in the setting of a scion in a diagonally cut surface, produced 
by the cutting off of the tip from the stock where it is of the same thickness 
as the scion. Most nearly related to this is the single and double saddle 
graft. The scion and stock can be united also by actual longitudinal surface 
wounds, if the stock is cut at the side in only one place without loosening its 
tip. The scion either remains attached to the parent plant and, likewise, is 
cut only at the side (ablactation), or cut off from the branch, as in other 
forms of grafting, it is fitted to the stock by lateral paring. In order that 
the scion may fit more closely in a lateral position, its lower end is cut to a 
wedge and this end is forced into a cleft at the base of the surface wound 
of the stock. In many plants (Camelias) the scion is not infrequently cut 
to a short wedge and this wedge is forced into a lateral cleft in the stock, 
produced by a short diagonal downward cut into the wood (insertion). 
When the grafting fails, stock thus cut suffers least of all and after a short 
time can be used again. 

The injury from which the trunk suffers most is the cleft wound. The 
form of grafting with such wounds is cleft grafting. This was at first used 



^?,2 




833 

generally in Germany but now only for isolated, special cases to rejuvenate 
older trunks. Cleft grafting consists of pushing a scion, cut wedge shaped 
on two sides, into a cleft in the stock which has been cut off square. This 
cleft is produced by splitting or by cutting out a wedge from the wood. 

In considering the processes of healing, i. e. processes of union in the 
different forms of grafting, we must distinguish first of all whether this has 
been carried out on soft wood, or on branches of mature, strong wood. In 
the first case more tissues participate in the formation of the "layer of 
union" than in the latter case in which a mass of tissue is chiefly involved, 
formed from the cambial zone (at times also from the pith zone). This 
tissue forces itself into the space between the scion and the stock, or figur- 
atively speaking must pour in between the two adjacent parts. 

OCULATION OR BUDDING. 

The most interesting processes of union are found in oculation. In the 
plate here given, a budded rose is pictured. In one-half of this drawing 
(from I to ^), the tissue structures are shown after six days; in the other 
half (from 2 to j) after about four weeks. The section through the place 
of budding clearly shows the inserted bud at E, the stock at w. In the 
stock, hh is the old wood of the previous year, sh, the wood of the current 
year, formed at the time of oculation. R L are the bark strips, raised by the 
T-cut ; in them, h should indicate the phloem fibres, t the dead tissue of the 
cut edge. 

At the time the bark strips were spread out from, one another by the 
inpushing of the bud {E), the cambium was very active. The raising of 
the bark takes place here in the sapwood in such a way that the youngest 
vascular primordia (//) and the cambial layers (c) lying in front of them 
remained attached to the bark strips. 

Often only the bark is raised. In fact, under some conditions, pieces 
of the entire cambial region with the youngest bark cells remain attached to 
the wood. No evidence of any fixed law has been recognized in this con- 
nection. It seems that the momentarily tenderest part is torn when the 
bark is raised and that individual homologous tissues can behave differently 
at the same time in the same varieties ; in fact, that even the bark on the 
different sides of the trunk has a different loosening quality. Therefore, 
the processes of healing are unlike in the same species and variety even in 
the same grafted individual at different heights. 

Even after 12 hours a change in the peripheral cell layers may be recog- 
nized on the edges of the wound in the bark as well as in the wood; the 
walls of these cells have thickened and turned yellow, either on the exposed 
side alone, or on all sides of the cell ; the cell contents have increased. It 
cannot be determined whether this has taken place only because of swelling, 
as in the wall, or by the transference of material from the inner part of the 



834 

wood toward the periphery. The first developmental stages differ according 
to the life activity of the exposed cells. As a rule, all places on the exposed 
wood are not covered with sapwood capable of increase. If the tissue of 
the sapwood does not begin to increase, the cell walls on the edges of the 
wound swell and turn brown, together with their contents ; they also collapse 
somewhat and form an irregular thick yellow stripe. The walls in the cell 
groups, which are adjusting themselves for increase, usually turn brown 
only slightly and frequently after a short time begin to form wound callus. 
The thin-walled tissue, gradually growing out in parallel rows (ok), is the 
wound tissue, the growth conditions of which were described under wounds 
due to barking. In Fraxinus, for example, this could be observed to be i6 
cells thick after two days. The arrangement of the callus is comparatively 
rarely as regular as it is shown in the drawing. Because some parts of the 
wood do not form wound callus, the adjacent cell rows radiate from one 
another and cover over the places remaining inactive. This callus forma- 
tion is so rapid that the covering of the inactive places and the close union 
of the elements coming from the different sides is a matter of course. 

The bark strips on an average proceed less rapidly to the formation of 
wound callus. The products of the new formation are also different. To 
be sure, the peripheral cells, rich in cyptoplasm, project somewhat (k) soon 
after the operation, but cell increase does not always occur or, in case it 
does begin, its product is only cork which can protect the wound surface. 
The formation of new structures is more energetic and increases until an 
abundant wound callus tissue is formed usually first toward the inner angle, 
where the bark strip is firmly attached to the wood (ok). 

The rapidly formed wound callus masses of the bark and wood, as well 
as ultimately those of the scion, unite and in the shortest possible time form 
a temporary protection for the graft wound. We say "a temporary protec- 
tion" for, actually, the tissue as yet reproduced is only short-lived. As soon 
as the the callus tissue has acquired a considerable extent and seems exposed 
to increasing pressure, a meristem zone is formed in it at a certain distance 
from the peripher}^ which at times is strengthened by cork cells. The 
maturing of this meristem zone depends upon the distance between the stock 
and scion. At times, at a very short distance, only a few lateral, isolated 
aggregations may be recognized but when the intermediate space is great 
and the wound callus formation luxuriant, continuous zones may be discov- 
ered, which often after having a looped course are connected with the 
sharply protruding cambial zone of the older overgrowth tissue formed on 
the bark strips (cc,cc). 

The meristem zone is not drawn in the young wood callus because it 
does not appear until later. 

In common with the cambial zone of the bark strips (cc), this callus 
meristem furnishes first of all the actual connecting tissue consisting of 



835 

wood parenchyma in the form of thick-walled, isodiametric cells, or cells 
somewhat stretched radially, irregularly quadrangular, which appear not 
infrequently with somewhat bent walls (kg). These represent the begin- 
nings of a wood body, which is being formed under slight pressure. By 
their increase they gradually compress all the thin-walled, first-formed 
tissue, retaining the character of phloem parenchyma (ok) and representing 
the first closing of the wound. When the meristematic zone is formed in 
loops, round masses of wood parenchyma are produced, enclosing the brown 
dead cell complexes of the original tissue. Gradually the whole tissue (ok) 
is pressed back between i and 2 by cells similar in character to those marked 
(kg), which store up starch. 

Under favorable conditions, the scion also participates in closing the 
wound. In the present drawing, a bud is shown with the bark shield, but 
without any wood. The cut £ is a cross section only through the bark 
shield. The bud belonging to this, which must be imagined in the direction 
(0), lies above the plane of the section ; in this section only the large central, 
vascular bundle (gb), which extends to the bud, and a smaller one adjacent 
to it have been drawn. The third, smaller bundle, present in every unin- 
jured bud cushion and likewise traversing slantingly the axis of the branch 
on the other side of the central bundle, has been cut away here in removing 
the bark shield; this does not affect the outgrowth of the bud. On the 
other hand, the absence of the central vascular bundle will always signify a 
failure in budding. The bark shield with the rapidly drying bud bracts can 
grow further without the vascular body but in my experience it has never 
happened that an excessively luxuriant overgrowth tissue from the bud had 
formed adventitious buds and in this way compensated for the dead bud. 

To be sure, the formation of adventitious buds takes place in many 
bud grafts, as is shown in the following Fig. 200 of an herbaceous bark 
graft of Aescuhis rubicunda on Aesculus Hippocastanum, but up to the 
present I have found this bud formation only on luxuriant overgrowth 
edges of the stock. The bark strips (ne) have produced such strong new 
structures that they have thereby been pushed out from the scion like wings. 
Numerous adventitious buds (a) stand on the edge. 

In the budded rose (Fig. 199), the whole inner surface of the bark 
shield (E) has already produced new wound tissue, sometimes more, some- 
times less, according to the age of the mother cells. The cambial zone of 
the bundle, lying below the phloem fibre groups (b), has formed the new 
cells very abundantly, as is shown by the protruding tip (2). The new 
structure on the inner side of the shield bears the character of bark tissue 
and is already distinguished by numerous crystals of calcium oxalate, while 
the cambial zone (c), which begins to form new wood elements, appears in 
later stages of the coalescence in connection with the cambial zone (cc) of 
the bark strips. As soon as this union takes place a continuous cambial ring 
is formed again about, the whole circumference of the tree. The cambial 



836 

zone of the bud represents an integral part of this. The zone (cc), if traced 
backward, is found to be a direct prolongation of the cambial ring of the 
uninjured axial part. 

If the wound is closed by the coalescence of the dififerent wound tissues 
and the union of their cambial zones, the thin-walled tissue of the wound 
callus (ok) has almost disappeared and has been replaced by actual uniting 
tissue in which groups of porous cells may be often distinguished from less 
porous ones, as mentioned above. As indicated by the bark tip (2-3) the 
wood parenchyma, which takes over the formation of a permanent union, is 
also produced directly and in fact in the angles where the bark strip and 
wood body join, i. e. where the indicating line from kg ends. When it is 
perceived that the bark strips (3 R L) have been so raised by the budding 
knife, that not only the whole cambial zone but also the young sapwood 
elements already differentiated remain attached to them, then it is evident 
that this connecting tissue is a product of sapwood cells already somewhat 
older (not those most recently formed). This tissue is not produced from 
th6 wound callus (which is never formed in the inner angles) but from the 
division of cells already destined to be wood cells and vessels. 

We have, therefore, three different factors which furnish a similar 
product, the wood parenchyma, already described as the uniting tissue, 
which takes over the process of uniting scion and stock. The first factor is 
the bark strip from the stock, the second the callus of the exposed wood 
body, the third the scion. The momentary strength of the different factors 
determines which one of these three actually produces the union in a grow- 
ing graft or bud. The variations which may be observed are extraordi- 
narily great. The quickest possible formation of wound callus, which takes 
over the temporary closing of the wound, is essential for the success of the 
graft. However, the union becomes permanent only if the cambial zone 
(cc) of the strips (R L) which forms the new wood and which I have 
occasionally called "the mobile ivound-wall" occurs in permanent union with 
the cambial zone (c) of the scion (or bud) and forms wood elements 
remaining in a connected layer. The mobile wound-wall shows the charac- 
ter of the usual overgrowth edge by its cambial zone which is spirally 
twisted on the free side, and distinguished from this overgrowth edge, the 
"fixed wound-wall," by the large, inpushed zone of wood parenchyma (kg), 
which passes out from the fixed wound-wall. The point of union of the 
cambial zones of stock and scion (or bud) is recognizable not only in the 
year of the union but remains so for many years, by the course of the wood 
elements. In the line of union, which extends from c to cc, the elements 
are more or less strongly elongated tangentially, while in the interior of the 
wound-wall they have already assumed the normal vertical arrangement 
and, therefore, in cross section appear actually cut across (hK), thus resem- 
bling the normal wood (hh). If, in the production of this uniting tissue, 
the cambial zone (c) of the scion (or bud) unites with that of the stock (cc) 
to form a continuous ring, it is evident that this ring is not evei;ywhere 



837 



equally distant from the centre as in an ungrafted or unbudded trunk, but at 
s and cc shows a deep depression, an S-like curvature. This curved line of 
union, Gopperfs "line of demarcation," is visible to the naked eye and is 
noticeable even in the bark covering^. 

In the second, usual method of budding "with a heel," the bud is cwf/rom 
the branch with a little piece of wood attached and is shoved into the stock. 
In this the processes of healing vary somewhat from those described above. 
The disadvantage in this method is a retarding of the union ; the advantage, 
however, lies in the increased certainty of preserving the bud. In separating 
the bark shield from the wood body, 
for the purpose of bark budding, the 
actual bud cone is not infrequently left 
on the branch if its vascular bundle 
cylinder has been too greatly lignified. 
The bud on the bark shield then has a 
hole on its underside and does not 
sprout. Untrained workers overlook 
this little hole and bud in vain. 

The same process of healing, as in 
budding with a heel, is found in hark 
grafting. Only in this case the stock is 
more injured since it must first be cut 
square off, then the bark on one side is 
split and somewhat raised for the in- 
sertion of the scion as is done in bud- 
ding. Instead of the single eye a diag- 
onally cut branch is used, bearing 
several buds. The slanting cut surface 
forms simple overgrowth edges, i. e. 
fixed wound-walls, which unite with 
the mobile wound-walls of the bark 
strips of the stock and the uniting tis- 
sue of its exposed wood surface. In 
bark grafting {"whip grafting"), how- 
ever, the stock has more to do and 

stores up less reserve plastic material, since the part of the cross section on 
the end surface of the stock not covered by the scion must also be overgrown. 

The luxuriance, to which the process of coalescence can attain in bark 
grafting on strong stock, is shown by the accompanying drawing (Fig. 200), 



nl- 




Fig-. 200. 



Bark graft of Aesculu.s, with 
adventitious buds. 



1 The difference between the present experiments and previous worlc lies in tlie 
proof of the different origin of the tissue of union or, according to Goppert, the "inter- 
mediary cell tissue." He tliinlis that tire production of tlie tissue whicli, in common 
with tlie cambium, takes over tlie coalescence, must come from the medullary rays, 
while Hanstein considers the whole tissue of union to be produced by the cambium 
alone. Actually, all elements, still capable of new formation, can take part in the 
formation of tlie wound callus and tissue of union. In many trees, for example, 
good instances of wound callus may be obtained which is formed from the pith 
body, particularly the pith crown. (Tilia.) 



838 

of the grafting of Aesculus rubicunda on Acsculus Hippocastamim, taken 

from nature. A few weeks after the grafting the new structures on the 

inner side of the bark strips («/) of the stock had become so extensive that 

they stood out Hke wings from the scion and produced adventitious buds (a) 

on the cut surface. 

Copulation and Grafting. 

In copulation, the lower end of the scion and the upper end of the stock 
are cut slanting, and, when possible, both are of the same size. The two 
cut surfaces are so fitted to one another that the respective tissues of both 
coincide. Thus we have here simply two surface wounds. These form 
complete overgrowth edges which push in between the scion and stock. 
When the manipulation is well carried out and the space between the wound 
surfaces very small, the closing of the wound is so perfect that even the 
microscope can show no spaces between the old wood of the cut surfaces 
and the compressed connecting tissue. Goppert finds that, in copulation, this 
connecting tissue dies in a young condition without disappearing, while in 
grafting, when the union is complete, it remains for a long time organically 
active. In my experience, no such difference dependent upon the method 
used has appeared in the length of life of the connecting tissue. In older 
cases, holes may indeed be noticed, or brown, decayed masses of dead tissue. 
It seems to me, however, that this would occur in all grafting without any 
distinction as to method used, if the wound by very careful adjustment of 
stock and scion has been closed by the wound callus first produced without 
any subsequent formation of woody parenchymatous connective tissue in 
the union. Copulation may, therefore, retain the value and the universal 
application which it has had up to the present. However, I consider the 
simplest form to be the best and the so-called English grafting, as well as 
Thouin's methods (Miller, Kiiffner, Ferrari, etc.) disadvantageous or even 
injurious and trifling. 

Cleft grafting may be considered as the most dangerous operation. The 
stock is usually cut off square and split once, or several times, deep into the 
wood. The scion is cut wedge shape and so clamped in the cleft that its 
cambial zone forms the connection between the two parts of the cambial ring 
of the stock separated by the cleft. In case the wedge-shaped scion is not 
herbaceous, it will on both sides produce wound walls from the remaining 
part of its cambium alone. This occurs also on the split edges of the stock. 
The united connecting masses will endeavor to fill out the space in the old 
wood. On an average, this succeeds very rarely; in spite of the grafting 
wax, moisture penetrates into the split from the square cut surface of the 
stock and easily causes decay or allows some fungus to enter. 

The process of grafting naturally does not depend upon the existence 
of a definite cambial zone but will be possible also in monocotyledons. 
DanieP gives an example of this ; he carried out grafting experiments suc- 
cessfully with Vanilla and Philodendron. 

1 Daniel, L.., Greffe de quelques Monocotyledones sur elles-rrffemes. Compt. rend. 
1899, II, p. 654. 



839 

In concluding this consideration of the healing processes of wounds, it 
should be emphasized once more that the decision as to the relative value of 
the grafting method used refers here only to axes at least one year old and 
already provided with well developed wood. In grafting the, soft wood of 
woody plants, or herbaceous plants, the choice of method may be governed 
by purely practical considerations. In the coalescence usually so many 
elements of the cut surfaces (older bark and wood elements in pith) partici- 
pate in the formation of wound callus that a close union takes place under 
all circumstances favorable for the plant body, provided, of course, that a 
sufficient relationship exists between scion and stock. 

The Longevity of Grafted or Budded Individuals. 

It cannot be denied that, aside from the possible action of different 
peculiarities of the two grafted parts on one another, grafting influences the 
development of the individual. As Duhamel has already emphasized, the 
tissue changes at the place grafted will at any rate cause a change in the 
conductive capacity. The connecting layer will produce retardation of the 
water conduction and an easier storing up of the descending, plastic ma- 
terials in the part which consists of wood parenchyma, rich in starch, as also 
later when the connecting layer is formed from interwoven prosenchyma 
elements. The results of these changes have already been discussed. 

The limit, up to which different individuals can be united with one 
another to form a persistent, normally functioning organism, as yet little 
understood, may be determined by the fact that, in general, only plants of 
the same natural families can be grafted (or budded) upon one another with 
any prospect of success. According to all previous experience, this would, 
however, represent the extreme limit. A sufficient number of examples are 
known of cases where members of the same family cannot be united perma- 
nently. In fact, varieties of the same family can remain united for a few 
years and then in the end break the union, in which case, as a rule, one part 
dies. It is probable that, aside from the material relationship, a similar 
biological development is absolutely necessary in the two individuals which 
are to unite. I, therefore, believe that the different beginning and end of 
the vegetative phases (leaf formation, setting of fruit, etc.) and the different 
amounts of water needed by the individuals is very decisive for the perma- 
nence of even those unions which were successful in the beginning. Often 
such cases of grafting remain fresh for many months without any firm 
union. In herbaceous grafting of heterogeneous varieties, or organs, it is 
found that the scion often continues growth and develops a sickly inflor- 
escence but finally dies. So far as I have had insight into this matter, no 
union had taken place. Both parts may have done their best ; all their 
tissues, capable of developing further, can produce new structures and 
even, in places, a nominal wound callus but a brown stripe extends 
between the tissue masses of both parts, which shows at once to which 
individual the tissue in question belongs. The brown stripe is either formed 



840 

of the swollen walls of the outermost cells, or caused by the collapse of all 
the cells of the wound edges.- Usually on the boundary a cork layer has 
been formed by the suberization of the walls of the peripheral parenchyma 
cells or, besides this, by the appearance of actual cork cells. 

In genera which finally unite, as, for example, Iresine on Alternanthera, 
it is found that for whole stretches of the grafted surfaces, the connecting 
tissues grow side by side, cut off from each other by a cork layer. 

Similar cases may be proved in root grafts {Bignonia) and it could be 
•observed in cleft grafts of Paeonia arhorea on fleshy roots of Paeonia offici- 
nalis that the root, as stock, had served only as a receptacle for the scion. 
This latter had formed roots without any union with the stock. 

Root grafting is in general a very good method. Even for our fruit 
trees it had been used by Sickler at the end of the seventeenth ( ?) century 
and later Seigerschmidt in Mako recommended it very highly^. Root 
pieces, varying in thickness from the size of a quill to that of one's thumb, 
seemed suitable, if provided with fine roots. They were cut in pieces eight 
to twelve cm. long, were grafted by copulation or cleft grafted and the place 
of union covered with earth until only two or three eyes extended above the 
soil. Trunks of old seed- or stone-fruits give an abundant material for 
stock, when they have to be removed. Of course, the roots must be very 
healthy. The method of grafting roses on pieces of roots in January or 
February has been adopted already. For Clematis and other woody plants, 
this method of grafting is becoming more and more of a favorite. 

It may be presumed from the very beginning that under certain cir- 
cumstances which condition a scanty coalescence, the life period of a graft 
will be very short. The question, wdiether'the process of grafting in itself 
limits the life period, as Thouin and Goppert have stated, must be laid 
aside. It cannot be denied that grafted fruit trees, on an average, are 
shorter lived than those grown on their own roots. It may even be granted 
that a dying of the trees, as Goppert has observed, is initiated in the line of 
demarcation by a gradual rotting of the place of union but it is not credible 
that this process of rotting may be the cause of actual death, or even of 
disease, in grafted trees. It is found, on the contrary, that even badly united 
copulants, which at first may have been simply stuck together on one side, 
can in the end give perfectly healthy permanent trunks. The old places of 
union have the firmest wood. A storm may twist the trees off more easily 
at any other place than at that of the union. Goppert's observations may 
possibly hold as the rule only in old trunks which have been regrafted later. 
I would explain the comparatively earlier death of grafted trunks by the 
fact that not only better but also more tender cultural varieties are used for 
grafting. These, aside from the disturbances which they undergo in the 
cutting, are in themselves more susceptible to disturbances in growth and 
to unfavorable weather than the specimens grown from the seed, which 
approach more or less the hardier nature of the stock. 
1 Weinei; Obst- und Gartenzeitung 1876, p. 587. 



841 

Mutual Influence of Scion and Stock. 

In regard to the influence of the stock on the scion, the experience of 
practical growers has shown for some time that apples set on Paradise 
stock retain a lower habit of growth and at times bear fruit even in the first 
year after grafting. In the Doucin the forms become larger and fertility 
begins after a few years, while the scion, on a stock of Pirus Mains, attains 
the usual tree form and bears fruit only after a considerable number of 
years. For pears, the quince and Crataegus, which love moist soils, 
form the best dwarf stock. For exposed or dry positions, Pirus Malus 
prunifolia major, together with P. M. baccata cerasiformis, the cherry apple, 
have been recommended from several localities as stock for apples^ P. M. 
prunifolia, originating in Siberia, is hardy and may be used as a street tree. 
It differs from the variety of P. M. baccata by its conspicuous, retained 
calyx. With the variety of P. M. baccata belongs also P. M. cerasiformis, 
which drops its calyx at the time of ripening. 

Lindemuth states, in regard to the life period of tree trunks, that varie- 
ties grafted on Paradise stock seldom live more than 15 to 20 years, while 
specimens grafted on seedlings of true tree varieties of Malus can become 
150 to 200 years old. Of the remaining literature, we will mention the 
following examples : 

Sour cherries grafted on sweet cherries thrive less well than sweet 
varieties on sour ones". Oberdieck found that sweet cherries bore abun- 
dantly on sour cherries. 

Treviranus" cjuotes that walnut and chestnut trees of the late sprouting 
varieties are said never to succeed on early sprouting varieties (according 
to Cabanis, Trait f de la grcffe). On the other hand, in seed fruits, this 
method of grafting later varieties on early ones is said to have good results 
and to bring about an earlier ripening of the fruit*. In peaches, grafting 
in itself, whether of early varieties on late varieties, or conversely, seems 
to give good results. Gauthier reported to the Parisian Societe cent, d' 
Horticulture' that he had grafted peaches in August or September on typical 
fruit spurs (coursonnes), as well as on those which have elongated, both 
late varieties on early varieties, and conversely. The fruits are said to 
become larger because, in the tree which is grafted with a late ripening 
variety, the fruit of the stock can be harvested first and then the tree can 
use its remaining strength to mature the fruit on the branches of the grafted, 
late variety. In the opposite cases, of grafting on late varieties, the whole 
tree becomes stronger because late varieties in general have a more luxuriant 
habit of growth. 



1 Lieb, Pyrus Malus prunifolia major. Pomolog". Monatshefte 1879, p. 130. 

2 Lindemuth, Vegetative Bastarderzeugung- durch Impfung. Landwirtsch. 
•Tahrbiicher 187S, Part 6. 

3 Treviranus, Physiologic der Gewachse II, 1838, p. 648 f£. 

4 V. Ehrenfels, tJber die Krankheiten und Verletzungen der Frucht- und Gar- 
tenbaume. Breslau 1795, p. 108. 

5 Ortgies, Vorteilhaftes Pfropfen von Pflrsichbaumen. Pomolog. IMonatshefte 
V. Lucas 1879, p. 6i. 



842 

An older example from Duhamel^ should be mentioned in this connec- 
tion. Almonds grafted on plums and, conversely, plums on almonds, at 
first grow very well but usually retrogress after one or several years. The 
almond has a much more luxuriant habit of growth, sprouts earlier in the 
year and, as scion, forms a strong roll at the place of grafting. It is 
probable, therefore, that such a scion, requiring more water earlier and 
constantly, will thrive on a less luxuriant stock as long as this is able to 
satisfy the young twigs from its reserve store in the trunk. If the grafted 
branch becomes several years old, its needs become greater and, if it cannot 
accommodate itself to the stock, as frequently occurs (dwarf trees of seed 
fruits), it gradually degenerates from a lack of nutriment. The results vary 
greatly, according to soil, amount of water and variety. Conversely, a 
stock which blossoms too early and grows too luxuriantly will supply more 
to a scion, requiring a lesser amount, than this can take up. The super- 
fluous material from the stock is quickly worked over into new structures. 
If many groups of buds are present, this excess manifests itself in the pro- 
duction of long shoots. If, however, as in grafting, most of the lateral 
buds, or eyes, are suppressed, the material remains at the disposal of the 
thickening ring of the trunk. Thus, instead of prosenchymatous elements, 
aggregations of wood parenchyma are formed, which, in the Amygdalaceae, 
easily become gum centres as I also have observed. Among the older 
observers, Duhamel reports that almond stock, grafted with plum scions, 
will die from gummosis at the place of grafting. 

Experience has also taught, in the very general practice of grafting 
pears on quince or apples on Paradise stock, that death sets in the more 
quickly for rapid growing scions, the drier the soil and the fewer the roots 
which the stock has developed in it. The scions fail much the more rapidly. 
Duhamel also cites cases when, under such disproportionate need of water 
in scion and stock, even simple transplanting has led to death through failure 
of union (almonds on plum stock), while the little trees of the same series, 
left standing in the nurseries, remain healthy. The pruning of the roots 
in transplanting has decreased too greatly the momentary capacity of water 
absorption in the stock. Peaches on prune stock are also said to give no 
especially permanent union-. The wood of the scion is said to turn red and 
soon degenerate. I would add here an experiment with the grafting of 
raspberries on Rosa canina^. Among rubus scions grafted by copulation, 
I found two branches developing on one specimen, one of which bore four 
normal raspberries. In the autumn, however, the scion died and, upon inves- 
tigation, the coalescence was found to have been very slight. On the upper 
part of the surface of copulation, only the stock had developed cicatrization 
tissue. On the other hand, on the lower part of Rosa, as on Rubus, abundant 
wound callus had been formed, showing normal processes of coalescence. 



1 Duhamel du Monceau, La physiqvie des arbres 1758, II, p. 89. 

2 Pomolog. Monatshefte 1879, p. 370. 

3 Sorauer, P. Rubus auf Rosa. Zeitschr. f. Pflanzenkrankh. 1898, p. 227. 



843 

Evergreen foliage seems to be no hindrance to growth on deciduous 
stock. Scions of Prunus laurocerasus on Pr. Padus, of Quercus Ilex and 
Q. Suher on Q. sessiliflora, of Cedrus Libani on Larix europaea are said to 
thrive but there is no report as yet as to a favorable growth of deciduous 
wood on evergreen stock. Thouin contradicts the former statement^ 

Of the noteworthy results of Duhamel's experiments, it should be men- 
tioned here that, for example, the fruit of the winter Christ pear on quince 
had a more delicate, juicier flesh and a finer, deeper colored skin, as con- 
trasted with scions grafted on wild stock. Leclerc du Sablon- observed 
that pears grafted on pears store up less reserve substances in their aerial 
parts than when grafted on quince stock, while the roots are poorer in 
reserve substances. This latter fact might be explained by the greater fer- 
tility after grafting on quince stock. 

It is remarkable that pears and apples, which form so perfect a union 
with remotely related stock, can never, or rarely ever, be brought to form a 
permanent union with each other. Numerous experiments have been made 
in this connection. Thus Knight'' reports a case of apple on pear stock, 
which for one year yielded an abundant harvest but died the following 
Winter. The fruit is said to have had blackened cores, not containing a 
single seed. Recent observers have affirmed this fact in general, but em- 
phasize the fact that exceptions may occur. Thus Stoll* reports that apple 
scions took well on pear trees and bore very soon but the fruit was small and 
the graft usually died in the fourth year. The head gardener, Seifert, in 
Segeberg (Holstein) describes a five year old apple graft on pear stock 
which in the fourth year had borne six well developed apples (Ribston 
Pippin). The apples had a good flavor but the crown of the tree had a 
weak growth. I have known of some favorable results from pear grafts on 
apples. In Czerwentzitz, near Ratibor, many examples were found of pears 
which had been grafted on apples. The method was in use at least ten years 
ago. In the first experiment (Geisshirten pear on apple) it was found that 
after the second year the fruit from pears on apple stock ripened two weeks 
earlier than on the main trunk. The scion lived eight years. Less vigorous 
stock gave no good results. Most varieties, to be sure, remained alive but 
made no growth. When the same grafting was repeated on the middle 
branches of the crown, a number of specimens died after two or three years. 
The others lived in a weak condition for some time without setting fruit. A 
note by Gillemot^ originates from this period. He had two-year-old pear 
grafts on apple stock and also had grafted cherry scions (Royal Amarelle) 
in the bark of a plum (Prunia institita). The scions developed very long 

1 Thouin, Monographie des Pfropfen.s. Berg-'s translation, 1824, p. 114. 

2 Leclerc du Sablon, Sur I'influence du sujet .sur le greffon. Compt. rend. 1903, 
CXXXV. p. 623. 

3 Hort. Transact. II, p. 201. 

4 Stoll, Das Veredeln von Birnen auf Apfeln. Wiener Obst- und Gartenzeit. 
1876, p. 10. 

5 Gillemot, Beitrag- zur Veredlung verschiedenartig'er Gewiichse aufeinander. 
Wiener Obst- u. Gartenzeit. 1876, p. 121. 



844 

shoots and bore comparatively many and handsome fruits in the second year 
but died after bearing. 

Up to the present, such experiments have been repeated on all sides but 
as yet no further desirable results have been attained than those known for 
a long time in regard to the use of dwarf stock. In some cases it was 
evident that the manner of grafting decided the success. Thus, for example, 
Carriere^ reports that the varieties of pears Bon chretien Rans, Doyenne de 
Juillet, Beurre* Gifford, Beurre Box. did not grow, or died soon after pro- 
ducing weak shoots, if they were budded on quince (greffe en ecusson). On 
the other hand, the results are considerably more favorable, if cleft-grafting 
is adopted and branch tips used as scions. The fertility is unusually great. 
Ligustrwn ovalifolium as stock is also said to behave differently with differ- 
ent varieties of lilac. Only Syringa Josikea is said to succeed when budded 
(greffe en ^cussion) while Syringa Emadi pcrsica and others develop well 
only when cleft grafted {greffi en fente). 

Recently special attention has been given this question in the grafting of 
grapes because of the struggle against the grape louse. The number of 
works on this subject is very great, so that we call attention only to a few 
important ones. First of all Couderc- determined, by questioning about 450 
French grape growers, that even the power of resistance of an American 
stock to the attack of the grape louse is usually somewhat reduced by graft- 
ing and also that the different varieties used as scions exercise an influence 
varying in intensity. 

Cases occur, however, in which a very vigorous scion can increase the 
power of resistance. Ravaz^, among others, lays especial emphasis on the 
fact that the stock influences the growth of the scion and also its fertility. 
We owe to Hotter* precise figures on the changes in grapes, due to the influ- 
ence of the stock. He investigated different varieties of grapes grown on 
vines grafted on Riparia and on self roots of vines of the same varieties. 
Among 9 varieties, yy per cent, of the juice from the grafted vines contained 
more acid than that from the non-grafted vines, of which 65 per cent, con- 
tained more sugar than those grafted on American stock. These statements 
are directly opposite to those of CurteP, who found the fruit of grafted 
vines larger, the skin thinner and the seeds less numerous but larger. The 
juice was richer in sugar than acid, poorer in ash elements, especially phos- 
phates, richer in nitrogenous elements but poorer in tannin. We have 
purposely cited both observations in order to show how differently the stock 



1 Carriere, Quelqiies observations k propos de la greffe. Revue hort. 1876, II, 
p. 20s. 

- From the Weinbau-Konj^ress of tlje 16th to 19th of August, 1S94 in Lyon; cit. 
Zeitschr. f. Pflanzenkrankh. 1895, p. 118. 

3 Ravaz, L., Choix des porte-gi'effes. Revue de viticulture 1895, Nos. 100, 
105, 106. 

4 Hotter, E., Der Einfluss der amerikanischen Unterlagsreben auf die Qualitat 
des Weines; cit. Centralbl. f. Agrikulturchemie 1905, p. 625. 

5 Curtel, G., De I'influence de la greffe sur la composition du raisin. Compt. 
rend. 1904. Vol. CXXXIX, p. 491. 



845 

can act. We find further experiences reported in the Memoirs of the Im- 
perial Department of Heahh in Berlin. 

Thus, for example, the twenty-fifth Memoir confirms the above men- 
tioned observation that the American vine, when grafted, loses in power of 
resistance to the grape louse, jaundice, etc^. 

In regard to the technic which has come into use in grafting grapes, we 
will follow Schmitthenner's- statements. He emphasizes the fact that, at 
present, the so-called English tongue grafting is almost universally used. 
This is a form of splice grafting in which the diagonal cut is not long but the 
cut surface of graft and stock have also an axial incision. The scion is split 
and shoved into the cleft of the stock so that scion and stock dovetail. Ana- 
tomical investigation shows that in grafting grapes the activity of the 
cambium is more reduced than in any other form of grafting; the annual ring 
formed after grafting is much weaker than the normal one. The influence 
of the wound is much more considerable than in grafting other woody plants 
and extends even to the next node, since all the ducts are filled with corky 
tyloses containing wound gum. 

Tompa^ had already given detailed anatomical data on grafting grapes 
in a herbaceous condition. However, the grafting of grapes will be com- 
pletely eflrective only if one uses as stock, not the American varieties, but 
hybrids of those which are adapted to the various localities*. 

Since the end of the last century, the formation of hybrids by grafting 
has been better understood. The best known example is Cytisus Adami 
which is said to have come from the grafting of Cytisus purpureus on Labur- 
num vulgare and, at times since 1826, has produced on different branches 
sometimes the blossoms of one variety, sometimes those of the other. 
According to A. Braun*^ the retrogression did not appear until sixteen years 
after the grafting. Laubert" found that retrogressive formation should be 
ascribed to a bud variation, in which the branch form, representing Cytisus 
purpureus, also completely resembles anatomically the true variety. Bei- 
jerinck'^ found that this bud variation could be incited often by wound 
stimulus. 

The description of a different example was published in 1875^. In an 
English grape house, a vine which had been grafted with Black Alicante was 
re-grafted some time later with three varieties on the Black Alicante as 



1 Funfundzwanzig'ste Denkschrift betieffend die Bekanipfunjar der Reblaus- 
krankheit. Bearbeitet im Kaiserl. Gesundlieitsamte bis October 1, 1903. 

- Schmitthenner, F., Verwachsung-sersclieinungen an Ampelopsis- und Vitis- 
Veredlung-en. Internal, phytopath. Dienst. 190S, No. 1. 

3 Tompa, A., Soudui-e de la greffe herbacee de la vigne. Annal Instit. ampelo- 
logique hongrois 1900, Vol. I, No. 1. 

4 Teleki, Andor, Die Rekonstruktion der Weingarten usw. Wien und Leipzig, 
Hartlebens Verlag, 1907. 

.". Bot. Jahresber. 1873, p. 537. 

6 Laubert, R., Anatomische und morphologlsche Studien am Bastard Labur- 
num Adami. Poir. Bot. Centralbl. Supplementary Volume X, Part 3. 

'' Beijerinck, M. W., Beobachtungen iiber die Entstehung- von Cytisus purpureus 
aus Cystisus Adami. Ber. d. Deutsch. Bot. Ges. 1908, Part 2, p. 137. 

8 Grieve, Ciilford, Bury .St. Edmunds, Singular Spoi't of a Grape Vine. Gard. 
Chron. 1875, p. 21. 



846 

stock. One of these three varieties, together with a small piece of its stock, 
was cut off later. Immediately a sprout, standing near the centre of the 
branch of the second inserted variety (Trebbiano) showed a spur with 
grapes which resembled absolutely the variety (Golden Champion) which 
had been removed. On either side of this abnormal spur, the Trebbiano 
stock bore its characteristic fruit. Therefore, no other hypothesis remains 
possible than that the Champion variety, which had been removed, had 
exercised an influence backward into the stock {Black Alicante) and 
through this to the laterally grafted Trebbiano variety. 

Lackner has cited another remarkable and older case\ He found in 
the garden Palavicini near Genoa, under the name Maravilla di Spana, an 
orange (Bigardia hizarro Riss.) which, on parts of its outer surface, showed 
callus excrescences and corresponding ones in the flesh, resembling in places 
a lemon, in others an orange and sometimes candied lemon peel. It has been 
proved that this form originated about 1640 when a gardener in Florence 
grafted some stock but the scion did not take. Directly beneath the place 
grafted, however, a branch appeared which bore this very remarkable fruit. 
The blossoms are likewise different, some being white, others red. 

In 1873 the "Revue horticole" published a case in which a Mr. Zen had 
bred new rose varieties by grafting. These varieties remained true. 

Focke- mentions a white moss rose which had been grafted on a red 
Centifolia. Such a plant developed bottom shoots which bore some white 
moss roses, some Centifolia and also moss roses with partly red petals. 
Besides the roses here described, Pirus, Begonia, Oxyria and Abies have also 
been named as genera in which graft hybrids can occur. 

Daniels found a backward action of the scion on the stock in one in- 
stance in which old pears, grafted on quince, had been sawed off 2 m. above 
the surface of the soil. Branches developed from these naked stumps, some 
bearing normal quince leaves, others mixed forms, between quince and pear^. 
This same author, in collaboration with Jurie, cites similar instances in 
grafted grapes. Of these, however, Ravaz* has proved that such variations 
also occur in non-grafted vines. Such cases of interchange occur often ; 
there is always a tendency to trace formal differences back to the special 
influence of the grafting, which, in fact, are only variations in luxuriant 
branches. Such variations appear also after severe pruning of the older 
axes. We need recall only the manifold leaf forms on the bottom shoots of 
Morus, Populus, etc., after the trunks have been sawed off. 

The majority of errors occur in grafting experiments on herbaceous 
plants. For this we have also examples by Daniel^ who grafted turnip 

1 Lackner, Einfluss des Edelreises auf die Unterlage bei Orang-en. Monatsschrift 
d. Ver. z. Bef. des Gartenbaues v. Wittmark 1878, p. 54. 

2 Focke, Die Pflanzen-Mischling'e. Ein Beitrag- zu Biologie der Gewachse. Bot. 
Centralbl. ISSO, p. 1428. 

3 Daniel L. Un nouvel de la grefCe. Compt. rend, 1903, Vol. XXXVII. 

4 Ravaz, L., Sur les variations de la vigne grreffee; response a M. L. Daniel. 
Montpellier 1904. 

5 Daniel L., Creation des varietes nouvelles au moyen de la greffe. Compt. rend. 
1894, I, p. 992. 



847 

rooted cabbages on Alliaria and this on the green cabbage. He found mor- 
phological and anatomical differences in the plants produced from the seed 
of the grafted specimens. Under this head belong also potato grafting 
experiments and the grafting of Solanum Lycopersicum on potatoes. In 
regard to the grafting of various Solanaceae on each other there exist very 
many experiments which we have described more fully in the second edition 
of this manual (cf., p. 692 if). The most thorough experiments, continued 
up to the present time, are those by Lindemuth, whose investigations have 
been considered under the section on Albinism (cf., p. 677 ff). Molisch^ 
has repeated earlier experiments and, agreeing with Strasburger and 
Vochting, has arrived at the conclusion that the production of graft hybrids 
may well be explained theoretically but has not actually been satisfactorily 
proven since, as he says, he and the others had found that scion and stock 
always retain their morphological character. 

We are not able to share this point of view since Lindemuth's'- latest 
experiments, as well as those of E. Baur, sufficiently demonstrate the influ- 
ence of the scion on the stock. Nevertheless, bud variations in many cases 
are also found which have nothing to do with the material influence of the 
scion on the stock but are probably traceable to wound stimulus. Arrest- 
ment phenomena of very different kinds, as, for example, increased pressure 
in the bud, can initiate a different development of the young axis. 

The influence of the stock on the scion is a well known fact in horticul- 
ture. We will recall only the dift'erent effect of the stock on one and the 
same apple variety. Grafted on Doucin, a stronger wood growth and a 
later fertility was produced, on Paradise stock a lesser wood growth and an 
earlier setting of fruit. No general rule may be laid down. The result 
depends not only on the plant variety but also on the accessory conditions 
(age, habitat, form of nutrition, etc.). 

The Natural Processes of Coalescence. 

Very frequently we find in hedges the union of two branches, which 
oftentimes have grown toward each other from opposite directions. The 
same phenomenon may be observed in roots in dense tracts of trees. 

The root fusions can take place in a young stage of the organ at a time 
when the epidermis is still capable of division. According to Franke^ this 
process appears in the ivy {Hedera Helix) and the wax flower {Hoy a car- 
nosa), in both of which plants the epidermal cells of two adjacent roots 
grow toward each other like papillae and unite. These cells then divide and 
thereby produce a few layers of connecting tissue. This, however, does not 
have the firmness of the connecting tissue produced from the cambial zone 



1 Molisch, H., tJber Pfropfungen. Lotos 1S96; cit. Bot. Jahresber. 1897, I, p. 155. 

2 Lindemuth, H., Kitaibelia vitifolia Willd. mit g-oldg-elb marmorierten Blattern. 
Gartenflora 1889, p. 431. tJber Veredlung-sversuche mit Malvaceen. Ibid. 1901, No. 1. 

3 Franke, Beitrage z. Kenntnis der Wurzelverwachsung-en. Beitrage z. Biologie 
der Pflanzen von F. Cohn, VoL III, Part 3; cit. Bot. Centralbl. 1882. Vol. X, No. 11, 
p. 40L 



848 

in two bark-covered roots of older, woody plants. The same process sets in 
here as in the union of aerial organs. The bark on the surfaces of contact 
is sometimes pushed toward the outside, sometimes enclosed like little 
islands ; the cambium no longer increases where the pressure makes itself 
felt on the places of contact, but unites from a common layer, enclosing both 
roots. Each year, when properly nourished, this layer forms new wood 

layers above the place of union. 
In regard to the anatomical 
conditions in the coalescence of 
tree trunks, we will refer to 
Kiister's different works^ and 
will mention here only one rare 
case which we have observed 
personally. This was found in 
the Ellguther forest, near Pros- 
kau, in a pine ; at several places 
on its trunk a second, thinner 
trunk had grown fast by natural 
in-arching. 

The base of the weaker 
tree had been cut off many years 
before so that the trunk was 
obliged to draw its nourishment 
entirely from the older pine. At 
the time observed, they were 
perfectly healthy, and formed a 
common crown ; only it seemed 
to me that the in-arched, root- 
less trunk bore somewhat 
shorter needles. 

I possess a piece of the 
trunk of another pine in which 
the tip of a branch, possibly five 
cm. in diameter, had bored into 
the main axis and there disap- 
peared entirely. This is an 
example of so-called "handled 
trees." 

All processes of this kind 
arise from the ability of the cambial tissue to form connecting layers between 
different axes. The processes differ from grafting only in the previous 
separation of the cambial layers by the bark of the plant parts ; these layers 

Woind^VooS "^'^ Pflanzenanatomie. Jena 1903, Gustav Fischer, p. 173, Section 




Fig". 201. Pine from the Ellguther forest in 

which one trunk has continued to nourish a 

second, rootless one connected by natural 

grafting-. 



849 

unite later. The bark must have been removed by gradual rubbing. If the 
union of the axes takes place of itself, a connected wood covering is depos- 
ited each year over the place of union. Often rather larger brown pieces of 
dead bark are incorporated in the surface of the union. This may be 
explained by the uneven formation of the two axes which have come in 
contact. If two trunks, covered with bark scales, touch each other, the 
most prominent places are rubbed down first and unite, while more deeply 
lying hollows do not participate in the union but are enclosed by the new 
tissue. 

In forests and especially spruce and pine tracts, twin trunks are fre- 
quently met with, which, beginning at the base, had united for different 
distances. Less frequent are the cases in which the upper parts of the main 
axes of separate origin have grown together. 

A cross section of the base of a twin trunk often shows three centres. 
In conifers, the middle, third stem has, as a rule, become very resinous. At 
any rate, the top of the main axis was broken off when young and two 
lateral eyes have taken over the growth. Instead of forming horizontal 
branches, these have developed into two top shoots which, after a consider- 
able number of years, have suppressed the dying main axis and finally over- 
grown it. Their overgrowth edges have gradually united so that, finally, 
one single, united cylinder has come from the three axes. 

According to the experiments mentioned under grafting, it may be 
assumed as a definite fact that a union can take place between parts of indi- 
viduals of different kinds. Spruces and firs, apples and pears, with each 
other and on quinces, or almonds and plums, and the like, may serve as 
examples well known to all. Nevertheless, a limit in the relationship of the 
plants certainly exists here, beyond which actual coalescence cannot take 
place in spite of the closest contact and vigorous rubbing. To be sure, a 
whole list of reports on the union of very heterogeneous plants may be found 
in the literature on this subject but a part of these statements is based cer- 
tainly upon erroneous observations^ in which union was assumed where only 
overgrowth took place. 

Having so fully described the processes of wound healing, we may here, 
without being misunderstood, express the opinion that the apparently rigid 
wood body of a tree may be caused to take on all imaginable forms if the 
tissue produced from the cambium is confined in some way. It can be said 
figuratively that the wood trunk flows about any object standing permanently 
in the way of its growth in thickness ; it grows over it and can enclose it 
entirely. Examples of so-called encysted stones, fir cones and even animal 
mummies have frequently been observed. 

We can here omit the enumeration of special cases, since we now 
possess a number of most interesting books about remarkable trees and all 



1 Moquin Tandon, Pflanzen-Teratologie, Schauer's translation, 1842, p. 274. 
Masters, Vegetable Teratolog-y 1869, p. 55. 



850 

kinds of botanical nature curiosities. The one by Ludwig Klein^ may be 
the most instructive at present. This seems especially fitted to arouse and 
increase a love of trees by its more than 200 illustrations, made from photo- 
graphic exposures. 

Wound Protection. 

We have already partially discussed natural wound protection in so far 
as it is produced by cork formation. In the wood body of trees, however, 
no cork deposit is found rapidly covering the surface of the wound, but the 
vessels in all such places are filled with tyloses or a gummy substance 
(wound gum) usually easily soluble in boiling nitric acid (dissolved with 
difficulty in the Correae). This is found when healthy wood adjoins the 
dead wood. As a rule, the tyloses are accompanied by some gum formation. 
Both kinds of filling make the wood of the branch stump absolutely imper- 
vious to water and air and quickly close the wound within the period of 
growth. It is evident from this observation that we would do well to thin 
our trees in winter shortly before cambial activity begins-. 

In a great number of woody plants, the vessels and frequently many 
of the other wood elements are filled with calcium carbonate^. This is 
found, as a rule, in the heart wood and those tissues of which the cells have 
a chemical and physical constitution resembling heart wood, such as the pith 
enclosed by the heart wood and the dead, discolored wood of knots and 
wounds. This filling is usually so complete that, after such pieces of wood 
have been burned, solid calcium casts of the cells are found which had con- 
tained the carbonate. The process may be explained as follows : whenever 
opportunity is afforded, the soil water, containing the calcium in the form of 
bi-carbonate, quickly passes through the wood cells and vessels, and gives 
off carbon dioxid ; it also deposits the calcium, which is no longer soluble, 
as a precipitate on the inner side of the vessels. In living heart wood which, 
unlike the growing sapwood, cannot quickly work over the calcium salt, each 
increase in temperature will cause the giving off of carbon dioxid and induce 
the precipitation of calcium. In wounds, the carbon dioxid will likewise 
disappear because of the exposure of the tissue. While the sapwood, which 
deposits no lime, protects itself from the entrance of air by the formation of 
tyloses or gum (probably as the result of the entrance of air into vessels 
previously filled with sap) we find in heart wood a deposition of lime as a 
means of protection. 

In the normal trunk, the formation of heart wood occurs first in the 
advance stages ; after injury, however, it sets in at once and gives rise to the 



1 Klein, Ludwig-, Bemerkenswerte Baume im Grossherzogtum Baden. Heidel- 
berg' 1908. "Winter's Universitatsbuchhandlung. 

2 Bohm, tJber die Funktion der vegetabilischen Gefasse. Bot. Zeit. 1879, p. 229. 
The most abundant literature on the formation of Tyloses may be found in Kiister, 
E., Pathologische Pfianzenanatomie, 1903, p. 98. 

3 Molisch, tJber die Ablagerung von kohlensaurem Kalk im Stamme dicotyler 
Holzg-ewachse. Sitzungsber. d. mathemat.-naturwissenschaftl. Klasse d. k. Akad. 
d. Wissensch. zu Wien., Vol. LXXXIII, No. 13 (1881). 



851 

false heart zvood formation^ which, through the action of fungi and bac- 
teria, can be transformed to heart rot-. 

This attack by micro-organisms has led to the establishment of a num- 
ber of parasitic diseases, which, however, essentially arise from disturbances 
in the process of wound healing. As first in importance, we will name 

Wound Gum. 

Prillieux describes this disease as "Gommose hacillaire," and Viala as 
"Roncet." The leaves remain green but become irregularly cleft and de- 
formed. In cross section, the wood shows black points and specks which 
enlarge and loosen its structure. Later the phloem separates from the 
xylem. On the cut surfaces from which the disease spreads, clefts arise 
which are infected by saprophytes. Prillieux found that the plant died 
after three to five years. 

The black points in the wood arise from a brown, gummy deposit, which 
fills the vessels and cells of the wood parenchyma and swarms with bacteria 
(motile rods). PrilUeux found in an infection experiment, made in May 
in the laboratory, the characteristics of the disease, which bear great resem- 
blance to those of Baccarini's "Malnaro." 

Viala and Foex, as well as Mangin, disagree with Prillieux, in that they 
hold that the described phenomena of disease can be produced by very dif- 
ferent causes and are not absent even in healthy plants. 

This difference in opinion was settled by Rathay"', who proved first of 
all that gum can occur in perfectly healthy vines. He found gelatinous 
threads in healthy, one-year-old shoots of Vitis riparia, extending from the 
ducts and composed of gum. The vessels filled with gum {"gum cells") 
may be seen in Fig. 202, i. This gave the color reactions of the pentoses. 
In Vitis vinifera, V. Labrusca, V. Solonis, V . arisonica, etc., the reaction is 
found only in wood two or more years old. If this process occurred in young 
vines, it could not be observed until July, when the gum is pressed out. In 
the root, gum formation is less abundant. 

As Rathay reports, even in the grapevine, a normal heart wood forma- 
tion may set in finally in plants twenty years old but takes place irregularly 
since scattered places of the inner sapwood are involved in the change and 
produce the brown spots, which Prillieux has described as the symptoms of 
Gunimose hacillaire. When such a brown place, extending backward like a 



1 Tuzson, J., Anatomisclie und mykologische Untersuchung-en iiber die Zer- 
setzung- iind Konservierung des Rotbuchenholzes. Berlin 1905, cit, Centralbl. fiir 
Bakt. 1905, 11, Vol. XV, p. 482. 

2 Herrmann, tJber die Kernbildung bei der Buche. Naturf. Ges. Danzig-; cit. 
Bot. Centralbl. 1905, Vol. XCIX. 

3 Rathay, E., tJber das Auftreten von Gummi in der Rebe und iiber die "Gom- 
mose bacillaire." Krenila, H., tJber Verschiedenheiten im Aschen-Kalk- und 
Magnesiagehalte von Splint-, Wund- und Wundkernholz der Rebe. Jahresber. d. k. 
k. onolg. u. pomolog'. Lehranstalt in Klosterneuburg. Wien. 1896. 



852 

thread in the sapwood (Fig. 202, 5) is examined, it is found that the broad 
vessels are filled with a brown gummy mass in which are crystalline precipi- 
tates of calcium carbonate (k) ; the contents of the wood parenchyma and 
medullary ray cells surrounding the vessel are deep brown and the adjoining, 
narrower vessels (e) are filled with tyloses. Starch is found only in the 
sapwood; in the heart wood, instead of the starch, brown grains are found 
which turn to bluish black with ferric chlorid. Stoppages of the vessels are 
not found in the sapwood but only in the heart wood. They are caused 
primarily by tyloses, which occur exclusively in the inner heart wood, while, 
in the outer heart wood ring, stoppage by gum or calcium predominates. 
Often whole rows of vessels in summer wood are filled with calcium, usually 
in the carbonate but at times in the oxalate form (Fig. 202, 4). The calcium 
carbonate, deposited in the youngest parts of the heart wood, is dissolved 
later. In the same way, the great amount of gum in the sapwood disappears 
with the change to heart wood. 

The tissue next to the wound surface in a horizontal wound dies back, 
more or less. In the living tissue immediately underlying this, the vessels 
are stopped up by means of gum, farther back by the formation of tyloses. 
The fact that the vessels have drops and layers of gum only on the parts 
adjoining the wood parenchyma cells, while the gum is lacking when they 
adjoin neighboring vessels, proves that it is the wood parenchyma cells 
which excrete the gum. The changes which characterize the heart wood 
begin much earlier on wound surfaces than on normal uninjured trunks, 
extending backward, however, only so far as the wound stimulus was effec- 
tive. On this account, it is termed "wound heart wood," by some observers 
"false heart wood" in order to distinguish it from true heart wood. Many 
bacteria are found near the cut surface but not in the deeper part of the 
various centres of heart wood formation, beginning at the wood surface and 
extending as light brown tissue stripes through the sapwood. Since the 
disease agrees in appearance with Gummose hacillaire, it is understood to be 
an immediate result of injury in older parts of the trunk. This wound 
stimulus may act chiefly on the protoplasm of the wood parenchyma cells 
surrounding the vessels; it may be continued further because of the con- 
tinuity of the protoplasm of adjoining cells and may incite the wood paren- 
chyma cells to a premature formation of tyloses. These cells, therefore, 
grow old and die prematurely. The normal secretion of gum, at first very 
abundant, ceases with the formation of tyloses. The process described is 
made clearer by an examination of the accompanying figures. 

In Fig. 202, 2 (an alcohol preparation from a ten-year branch of Vitis 
riparia), j indicates the boundary between two annual rings ; m,m medullary 
rays, g, gum cells, g vessels with strongly contracted gum contents. At the 
right (Fig. i), are reproduced two gum cells from a one-year-old shoot of 
Vitis vinifera (blue Tollinger) ; their contracted gum contents are seen in 
the centre. Only the inner outline of the cell walls is drawn. Fig. j is the 



853 






mi?^^ 





Fig-. 202. 



Stoppage of the ducts in a grapevine suffering from wound decay. 
(After Rathay.) 



854 

cross section of a brown wood thread from the sap wood of a very old vine ; 
j,j,j,i, the boundaries of the annual rings; k, a radial, fibrous crystalline 
aggregation of calcium carbonate imbedded in the brown gum mass of a 
broad vessel; the contents of the adjoining wood parenchyma, of the libri- 
form fibres and medullary ray cells are much browned and those lying 
nearest the vessels tt, are filled with tyloses. 

Fig. 202, 4, shows a vessel in cross section, the adjoining wood paren- 
chyma cells from a dead piece of wood lying under the terminal wound of a 
one-year-old shoot. Besides colorless gum, it contains radially arranged, 
stem-like aggregations of calcium oxalate. The lower figure is that of a 
vessel with the surrounding wood parenchyma from the heart wood of a 
very old grapevine. The vessel is filled with tyloses in which are contained 
crystalline aggregations of calcium carbonate (after Rathay). 

We have cited this case here because, as typical of many other cases, it 
proves clearly that the gum formation is the result of wound stimulus and 
at the same time shows how easily diseases may be listed as parasitic, in 
which is concerned only a subsequent infection by parasites which infest 
wounds. 

This concerns especially herbaceous, fleshy and juicy organs. In this 
connection, attention should be called to a work by Spieckermann^ who 
points out especially the resistance of a cork membrane to bacteria and the 
necessity of a definite high amount of moisture in the surrounding air as 
well as the water content of the tissue itself, aside from its specific sensitive- 
ness, in order to make possible bacterial decomposition even on a wound 
surface. 

The Slimy Exudations of Trees. 

In connection with the relation of parasitic infection to wound surfaces, 
already mentioned under "Gummose hacillaire," we will mention here the 
phenomenon where a usually sHmy, or gelatinous, and at time clayey looking 
exudation is noticeable very frequently in different kinds of trees, and even 
in summer remains moist and variously colored. 

According to our conception of the matter, an excessive bleeding of the 
trunk is involved here from wounds which cannot heal. Molisch- has 
proved that a local bleeding pressure makes itself felt in every wound which 
begins to be overgrown. In consequence of the injury, the cambium, as 
well as the parenchymatous elements of the wood and bark, is incited to 
increased activity and cell division. With this is connected such an increase 
of turgor that water is pressed out of the wound often under enormous 
pressure (at times, 9 atmospheres). 



1 Spieckermann, A., Beitrag zur bakterielleri Wundfaulnis der Kulturflanzen. 
Landwirtsch. Jahrbiicher 1902, p. 155. 

2 Molisch, H., tjber lokalen Blutungsdruck und seine Ursachen. Bot. Zeit. LX; 
cit. Just's Jaliresber 1902, II, p. 618. 



855 

If the analyses of the sap from bleeding grapevines are studied closely \ 
it is found that besides small quantities of organic substances, nitrogen, 
phosphoric acid and calcium are also present, i. e. it may be considered as a 
nutrient solution very well suited for infection by micro-organisms and for 
their increase. Ludwig has studied this thoroughly ^ In a number of pub- 
lications he describes a ivhite slimy exudation in the oak, birch, Saliceae, etc., 
due to Leuconostoc Lagerheimii Ludw. with which are associated various 
fermenting fungi (Saccharomyces Ludwigii Hans, etc.). A "brown slimy 
exudation," found in apples, birches, poplars, horsechestnuts and other fruit 
and street trees, showed Micro-coccus dendroporthos Ludw., with which is 
associated Trula monilioides Cord. Ludwig found a "red slime" in the late 
summer on the stumps of old, healthy beeches and observed in it a filament 
bacterium (Leptothrix?) and Fusarium moschatum. He met with the same 
bacterium in a yellowish white bleeding sap with a gelatinous, granular con- 
sistency in lindens and sometimes in birches. He also found toward the 
middle of April on fresh branch wounds of a hornbeam a milky looking slime 
which contained Endomyces vernatis Ludw. together with alcohol producing 
yeast. In one of his later works" we find mention of mites (Hericia) and 
eelworms (Rhabditis) as animal companions of such bacteria and fungi. In 
the Zeitschrift fiir Pflanzenkrankheiten 1899, p. 13, we find a list of all the 
inf esters of slimy exudations which have been confirmed not only for 
Germany but also for the tropics. Of course this list will be constantly 
increased according to whether the micro-organisms, belonging to specific 
localities, have had opportunity to infect the bleeding wounds of trees. 

The organisms here named may be considered to be injurious to trees 
only in so far as their infection delays or prevents the closing of the wound. 
Wounds which have been made by frost, Hghtning, animals, etc., and intro- 
duce periodic bleeding, form the primary cause of the slimy exudations. If 
it is found necessary agriculturally to remove such weakening causes, the 
only method possible would be to cut out carefully the diseased places and 
paint the fresh edges of the wound with coal tar. 



1 Ravizza, F., Uber das Thranen der Weini'ebe usw. Staz. sperimentali 1888; 
cit. Biedemiann's Centralbl. f. Agrik. 1888, p. 541. According- to investigations by 
Neubauer and v. Canstein (Annalen der Oenologie, Vol. IV, 1874, Part 4, p. 499) the 
sap of the grapevine (gathered in the dry year 1874) wliich, in its fresh condition, 
is as clear as water, and neutral, but easily becomes clouded by bacterial growth and 
then reacts as an alkali, contained at the time of experiment 2.1204 g. of solid matter 
per liter, of which 0.7408 g. were mineral elements and 1.3796 g:. organic substance. 
An analysis of the ash g^ave 10.494 percent, potassium; 1.437 percent, sulfuric acid; 
0.188 percent, ferric oxid; 2.822 percent, pliosphoric acid; 41.293 percent, calcium; 
5.534 percent, magnesia; 34.791 percent, carbon dioxid; 2.857 percent, chlorid; 0.810 
percent, silicic acid in the raw ash. Besides these acids, an orga,nic magnesia salt, 
g-um, sugar, and calcium tartarate, inosit, succinic acid, oxalic acid and unknown 
extractive substances, were found. Rotondi and Ghizzoni (Biedermann's Centralbl. 
1879, p. 527) also mention besides starch, sugar which the Neubauer investigations 
had not found in the fresh sap. Only the volatilized sap which, with the giving off 
of carbon dioxid and the elimination of calcium phosphate, togetlier with a yellow 
coloration, had a weakly acid reaction, sliowed all the sugar reactions. 

2 Ludwig-, F., Der Milch- und Rotfluss der Baume und ihrer Urheber. — ^tJber das 
Vorkommen des Moschuspilzes im Saftfluss der Baume; cit. Zeitschr. f. Pflanzen- 
krankheiten 1892, p. 159, 160. 

3 Ludwig, F., tJber die Milloen der Baumfliisse und das Vorkommen des Hericia 
Robini Canestrini in Deutschland. Zeitsch. f. Pflanzenkrankh. 1906, p. 137. 



856 



Root Injuries. 

Having thoroughly discussed the overgrowth processes of the aerial 
axis after all kinds of injury, we can quickly summarize the healing of root 
wounds. They correspond with those of the aerial axis and undergo modi- 
fications only inasmuch as the surrounding medium often interferes with the 
process of overgrowth. For example, if the soil is very moist, the stage of 
callus formation is prolonged, the transformation of the callus tissue to the 
firmer overgrowth edge is slower and 
the possibility of infection by wood de- 
stroying fungi greater. These factors, 
however, become less significant if the 
root wound surface is exposed to the air. 
The influence of light, warmth and dry- 
ness promotes the closing of the wound 
and removes any far-reaching influence, 
from even large wound surfaces, on the 
condition of health of the whole root. 
The best proof is found in much fre- 
quented forests in the vicinity of large 
cities where the superficial roots are 
constantly rubbed bare by pedestrians 
and, nevertheless, find opportunity to 
cover the edges of the wound with over- 
growth walls. The adjoining figure illus- 
trates such a root so worn that only the 
first formed annual rings are found to be 
still intact on the upper side. A cross 
section shows that no parasitic wound 
decay has occurred at the wounded 
place; the wood of the lower side is 
sound. 

The wounds produced in transplant- 
ing deserve the most consideration. 
Transplanting is a necessary process, 
which cannot be omitted in any nursery, 

for trade requires the delivery to the purchaser of trees which, after trans- 
portation to a permanent place, exhibit the greatest possible capacity for 
vigorous growth and development. 

In transplanting older trees with well developed tops and extensive root 
systems, a cutting off of the larger root-branches cannot be avoided ; hence 
the great danger of attack by parasitic root decay, which gradually advances 
into the trunk. But even if this danger has been prevented by the painting 
of the cut places with tar, the transplanting of old trees is always a danger- 
ous operation because the activity of the root system is retarded until new 




Fig. 203. A flat-lying- root of the 
alder barked by the tread of feet. 



857 

root fibres may be formed and the top, during this time, must draw water 
from the reserves stored up in the wood body. Because of the mutual 
dependence of the subterranean and aerial axes^ it is necessary to cut back 
the top of the transplanted tree, corresponding to the change in the root 
system. The further advanced the foliage of the tree, the more necessary 
is this pruning. In practice, other means for reducing, as far as possible, the 
evaporation of the aerial parts are used, such as, for example, the wrapping 
of the trunk, frequent sprinkling of the top, artificial shade, etc. 

Trees are usually sold from nurseries in a leafless condition but even 
here the quickly developing foliage requires a sufficient supply of water. 
This can be made possible only by newly formed roots. It is, therefore, of 
the greatest importance to deliver the trees in such a condition that they will 
form new roots as quickly and abundantly as possible. This depends upon 
the method of growing the trees and the way in which the roots have been 
cut. The older the root is, the scantier the development of new fibrous 
roots on the cut surface ; the larger the cut surface, the more slowly it is 
overgrown and the greater the danger of root decay. R. Hartig^ has thor- 
oughly described this for conifers and deciduous trees. 

On this account, the first rule is to grow the trees so as to avoid as far 
as possible wide spreading, large roots, such as trees usually form when 
developing undisturbed in one place and to produce a root system in the 
form of a ball of close standing, short but well branched roots. This is done 
best by repeated cutting of the roots in the first years of growth. 

Twisting the long tap root is often recommended instead of cutting it, as 
this would avoid decay. The widely experienced Goppert^ holds to this 
view. As a fact, twisted roots develop lateral roots quickly on their convex 
side*. In the water cultures of fruit trees, which I made in Proskau, some 
seedlings of the. apple, pear, pine, maple, etc., had curved tap roots because 
they had reached the bottom of the small receptacles and remained there for 
some time. The root tips of other plants were injured when taken from the 
sand. The majority of both kinds of seedlings developed lateral roots 
much sooner than the uninjured experimental plants, set earlier in larger 
i^eceptacles. This circumstance seems practical, as a confirmation of the 
view of those who recommend striving for early root branching in trans- 
planting by bending the tap root and not injuring it. We cannot, however, 
approve of this method ; in heavy soils, especially, where we had experi- 
mentally planted apple seedlings with cut back tap roots and others with 
uninjured but spirally twisted ones, the removal from the soil for the second 



1 Kny, L.., On correlation in the growth of roots and shoots. (Second paper.) 
Annals of Botany, Vol. XV, No. 60, Dec, 1901. 

" Hartig-, R., Die Zersetzungserscheinung'en des Holzes der Nadelbaume und 
der Eiche. Berlin 1878. — Lehrbuch d. Pflanzenkrank. 3rd. ed. Berlin 1900. Springer, 
p. 263. 

3 Goppert, Innere Zustande d. Baume nach ausseren Verletzungen. Breslau 
1873. 

4 Noll, Fr.. tJber den bestimmenden Einfluss von Wurzelkriimmungen auf 
Entstehung und Anordnung der Seitenwurzeln. Landwirtsch. Jahrbiicher 1900; cit. 
Zeitschr. f. Pflanzenkrankh. 1902, p. 55. 



858 

autumn transplanting was attended with much greater danger for the twisted 
specimens. To aid in the removal, the plants were pulled slightly and, in 
doing so, it became evident that the twisted specimens broke very easily at 
the first bend in the root. 

It is, therefore, advisable to cut the seedling tap roots at once at the first 
transplanting, so that several root branches are formed at the root neck; 
those near the cut surface develop new lateral axes in the second year. 

This makes possible not only an increase of the organs of absorption but 
also causes the production of a root ball in which the earth is held between 
the numerous roots. 

PrantF first studied thoroughly the anatomical changes which occur 
when younger roots, especially the germinating ones, are injured. He found 
in vegetables (peas, horse beans, etc.) that the loss of the tender root tip 
was completely made good by the development of a new one in which all the 
tissue systems participated if the injury took place close to the tip of the 
root. If he cut off the germinating root somewhat further back from the 
apical cell regeneration took place but all the tissues did not participate in 
this, only the juvenile vascular strands. The method of cutting, used almost 
exclusively in general practice, viz : the one injuring the mature tissues, 
does not bring about a regeneration of the root tip; instead of this, callus 
formation by the bark body sets in, thereby covering the cut surface. 

Nemec's" work is even more thorough and comprehensive. 

In contrast to the assumption that true regenerations, in which the part 
removed from the individual is directly formed anew in its original shape 
and with its original physiological peculiarities, rarely occur in the vegetable 
kingdom, experiments show just the opposite for roots. 

It is here only a question of injurying the youngest possible organs. In 
roots, restitution remains Hmited really to the zone where the cells on the 
whole wound surface (possibly with the exception of the epidermis and the 
outermost bark layers) are still meristematic. As soon as the cells of the 
outermost bark layers, together with the central rows of the sclerome, 
approach maturity, the meristematic cell layers alone, adjoining the peri- 
cambium, participate in the regeneration. It is found further that the vege- 
tative point of a root, of which the meristematic cells externally appear uni- 
form, still possesses a certain specialization. The cells are not equipotential 
and can not produce different tissues under arbitrarily changed conditions. 
Such specific differences are present in the "Statocytes." The mobility of 
starch grains in these presupposes specific peculiarities of the protoplasm, 
since in different callus-like hypertrophied cells starch grains are also formed 
which at times can be still greater than those of the statocytes and yet, under 
the influence of gravity, cannot be moved easily. The fact that, under the 
influence of a sufficiently strong centrifugal force, they can move cen- 



1 Prantl, Untersuchung-en iiber die Regeneration des Veg-etations-punktes an 
ang-iosp^;-m.en W^urzeln. AVurzburg- 1873. 

2 Nemec, B., Studien iiber die Regeneration. Bei'lin 1905, Gebr. Borntrager. 



859 

trifugally, proves that they are, nevertheless, specifically heavier than the 
cytoplasm. Therefore, the cytoplasm of the statocytes must have less specific 
weight and must be very fluid, i. e. it must contain very few elements of 
considerable consistency. Nemec also discovered peculiar cytoplasmic 
accumulations in the statocytes of the root cap, which certainly represent 
an especial reaction. 

If a young root is cut ofl: above its zone of growth and not within it, no 
regeneration but substitution takes place, for new lateral roots are produced, 
of which those nearest the wound surface are caused by their geotropic 
sensitiveness to grow down more perpendicularly than if they had developed 
from an uninjured main root. This makes possible the utilization of the 
soil layers for nutrition, which the perpendicular, downward growing main 
root would have traversed^ A fasciation of the lateral roots takes place at 
times after injury, or removal of the main root. Lopriore- was able to 
produce this fasciation artifically. 

Gnarly Overgrowth Edges. 

One universal characteristic in the overgrowth of wounds is that the 
wood fibres do not always parallel throughout the new structure but are 
often bent and twisted until at times they are looped. These variations in 
the course of the fibres form what is termed "gnarly wood." The adjoining 
figure of the overgrowth cap of an oak'branch, from which the bark has been 
removed, gives the best insight into this. The oak furnishes especially good 
examples of a complete closing of large wound surfaces by overgrowth and 
the luxuriance of the uniting wound edge not infrequently brings about the 
condition where, for example, in sawed ofif, larger branches, the newly 
formed tissue does not have a flat surface but one more or less strongly 
convex, becoming hemispherical to spherical in form. In such overgrowth 
caps small centres are often found, the so-called gnarl eyes (Fig. 203, a), 
around which variously twisted wood fibres (p) are deposited. By the term 
"gnarl eyes," however, actual buds are not understood but rather depressed 
tissue centres, around which are deposited the wood fibres in the form of a 
bowl and later serpentinely twisted ; in this way representing the "curly 
grain" in wood. While a spear-like, woody excrescence appears where 
actual eyes are produced, in gnarl eyes a deep depression is found formed of 
parenchymatous tissue, often increased by the rounding up and separation 
of the cells. Wood is deposited around this depression, normally composed 
of wood cells, medullary ray cells and vessels. The abnormality lies only in 
the bowl-like arrangement, recalling the gnarl tuber, and the frequent 
occurrence of medullary ray structures greatly broadened and resembling 
medullary spots, which at times can develop into secondary centres. 

1 Bruck, W. P., Unter.suchung-en iiber den Einfluss von Aussenbedingnngen auf 
die Orientierung- von Seitenwurzeln. Zeitsch. f. allg-em. Physiologie Vol., Ill, 1904, 
Part 4. 

- Lopriore, G., I caratteri anatoniici delle radioi nastriformi. Roma 1902. Note 
sulla biologia dei processi di rigenerazione delle cormoflte, etc. Atti Acad. Gioenia. 
Catania 1906, Vol. XXL 



86o 

We consider the curly or gnarly wood only as an extreme case of per- 
fectly normal processes, in the variation of the wood fibres when obstacles 
occur which prevent their longitudinal arrangement in the part of the plant. 
Such obstacles can differ greatly. Each normal branch insertion becomes 
the cause of a change in the course of the wood fibres surrounding it. The 
new formation of wood bodies within the bark, described under bark tubers, 
represents a further cause. Finally, however, we find the most varied 
phenomena of arrestment in the formation of an annual ring, produced by 
differences in tension in the growing axis. Such differences in tension are 
constantly present and are often strengthened by external influences. Frost 
action, for example, which causes the formation of parenchyma bands, is 




Fig-. 204. Gnarlly Wood structure of the overgrrowth cap of the stump of an oak 

branch. 



of especial significance. Another external cause is the contact of one 
branch with another. Besides mechanical pressure, conditions of light are 
also of influence; they cause variations in the nutrition of the different sides 
of the cambial ring. Internal processes of growth, as, for example, the 
rapid outpushing of a suddenly broadened medullary ray, are also of impor- 
tance. These can distend the bark into knobs, causing a repression in the 
growth of the adjoining wood layers and the like. All such disturbances 
must change the pressure conditions which the bark girdle in its entirety 
exercises on the cambium and will, therefore, influence the development of 
the wood formed from it. We find in the spiral twisting of the wood body 
in every trunk, hew greatly the course of the fibres is influenced by the 



86i 

pressure conditions, even in the normal trunk. Our experiments in binding 
a wire ring around a growing axis prove how much the wood fibres can be 
forced from a longitudinal into an approximately horizontal position by 
pressure. 

It is, therefore, the different pressure constantly endured and exercised 
by the bark girdle, which conditions the development and course of the wood 
fibres. Therefore, to explain gnarly wound wood, it is necessary to assume 
a theory of the polarity of the cells and the displacement of like poles as 
represented by Voechting and Mauled 

Bark Tubers. 

In concluding the chapter on the processes of wound healing, we have 
still to consider the production of spherical woody swellings, or tuberous 
outgrowths of the bark of trees and (more rarely) herbaceous plants. These 
structures are generally called "wood tubers" or "gnarl tubers." Their 
structure and production differ, thus necessitating a svibdivision into separate 
groups. Their character as correlative hyperplasias is their common quality. 
They are to be considered as the counteraction of the organism to previous 
phenomena of arrestment. The arrestment can consist in the cessation of 
the development of a bud or, independent of any bud, can be produced by 
the death of scattered tissue groups in the bark. The dying of different cell 
groups in the bark body of the woody axes occurs extensively. Frost and 
heat, local increase in pressure and the like, can cstuse the death of cell 
groups without any injury to the whole organism, which responds, not infre- 
quently, by an increased new formation near the centre of arrestment. The 
dead tissue groups are sometimes only encysted by cork layers, sometimes 
also accompanied by cell layers, increasing for some time, or permanently, 
according to the time and kind of disturbance and the amount of the nutri- 
tive supply in the surrounding tissue. The cell layers either produce only 
parenchymatous protuberances or cause the formation of new wood bodies, 
spherical in arrangement, with gnarled fibres. The latter process can 
increase to the production of independent tuberous wood bodies within 
the bark. 

I have made no personal study of the first group -of bark tubers, the 
production of which is traced back to bud primordia retarded in develop- 
ment, and in consequence will quote the descriptions of earlier authors. 
Trecul- should be named first among these. He describes in detail some 
cases of tuber formation (in the oak and hornbeam) and comes to the con- 
clusion that the tubers always owe their production to a bud which originally 
is directly connected vascularly with the wood body of the branch or trunk. 
Such a bud may lie dormant a number of years without projecting more 



1 Maule, C, Der Faserverlauf im Wiindholz. Bibliotheca botanica Part 33. 
Erwin Naegele. Stuttgart 1896. 

2 Trecul, Memoire sur le developement des loupes et des broussins, envisag'es au 
point de vue de I'accroissement en diametre des arbres dicotyledones. Annales des 
scienc. nat. 3 serie. Botanique t. XX, 1853, p. 65. 



862 

than 2 mm. (at least in the hornbeam) above the surface of the bark. After 
a few years of such lethargy, the fibro-vascular body can renew its activity 
and develop into a spherical, oval or even ellipical wood tuber. 

The death of dormant buds occurs of itself after a considerable number 
of years, if not hastened by external circumstances, since the connection is 
broken between the part of the bud lying in the bark and that in the wood 
body by the interposition of the wood mantle of the branch which bears the 
bud. ■ The outer part of the bud, covered with scales and lying on top of 
the bark, remains in place for some time; it dries up very slowly and finally 
is thrown off. 

This bud, originally attached to the wood body, can also be loosened by 
the splitting off of its fibro-vascular bundle from the wood of the trunk. As 
a rule, the portions of the bud which project above the bark surface die, 
while its fibro-vascular body, thus isolated in the bark continues to form new 
wood layers and its own bark without the aid of foliage ; it must, therefore, 
draw its plastic material from the surrounding green bark of the trunk. 
This growth may continue for years ; the outer side of the wood tubers may 
die from the destruction of external agents and, nevertheless, the tubers can 
continue to form new wood on the inner side. In the red beech, as in the 
hornbeam, these tubers are produced from adventitious buds. 

Til. Hartig^ describes the production of tubers in the red beech from 
preventitious buds. The weak basal buds in the red beech die after possibly 
twenty years inasmuch as the bud stem, lying in the bark, is separated from 
the part of the bud in the wood by the interposition of a completely uniform, 
connected wood layer of the branch bearing the bud. The part of the pre- 
ventitious bud lying in the bark, however, can remain alive for some time 
and leading, as it were, a parasitic life, grow by continued, concentric wood 
formation, into those wood tubers which, as large as peas or hazelnuts, 
project above the bark and are peculiar to the luxuriantly growing beech 
trunk in middle age. 

Dutrochet", whose personal view is related to the then prevailing bud 
root theory, describes the tuberous outgrowths as bud embryos (meri- 
thalles). Unlike the normal buds of the axis, these are not inserted on top 
of and between each other but remain without any connection with the other 
bud embryos and their vascular strands and, therefore, do not form a part 
of the axial cylinder. So long as such an embr}^o, the primordium of an 
adventitious bud, remains isolated in the other tissues, it develops no leaf and 
no bud but retains its spherical form and grows by constantly developing 
new wood layers, covered with their own bark. If this isolated wood body, 
the primordium of an adventitious bud, finally comes in contact with the 
axial body, its own bark disappears because of the pressure and the wood 



1 Hartigr, Th., Vollstandig-e Naturgeschichte der forstlichen Kulturpflanzen 
Deutschlands, p. 176. Berlin 1852. 

2 Observations sur la forme primitive des embryons gemmaires des arbres 
dicotyledones, 1837. (Nouv. Mem. du Mus. d'Hist. nat. IV). 



863 

knot forms a real bud, which develops leaves. It now represents a gnarl 
tuber (loupe) ; the coalescence of several such tubers forms a wen 
(broussin). 

This theory dififers from those developed earlier, inasmuch as in it the 
bud is considered the final product of the tuber formation, while in the 
others it is held to be the initial one. Lindley^ who describes the tubers 
mentioned by Dutrochet in the beech, cedar and poplar and who found in 
one poplar- that branches could develop from them, considers them to be 
produced from adventitious buds and cites a further case in old olive trees, 
mentioned by Manetti. He says that the tubers (gnaurs) in these trees 
were cut out, together with a part of the bark, and planted and that these 
tubers, which Manetti called Uovoli, gave young plants. Treviranus, to 
whom Morren sent some cedar tubers, confirms in general the structure of 
the tubers described by Dutrochet. He places in the same category the 
phenomena of the isolated vascular bundles (leaf trace strands) in climbing 
Sapindaceae, Calycanthus floridus and C. praecox, some Bignoniaceae, etc. 

Schacht-^ explains the tubers in the bark of poplars, lindens, beeches, 
etc., as dwarfed branches which have grown in circumference but not in 
length. While Hartig points to the first beginnings of the tubers in dormant 
buds, Ratzeburg* lays stress upon the bark as the productive centre of the 
same beech tubers and says explicitly that they do not extend to the wood 
body. Similarly Rossmassler"' declares that the tubers of thfe mo'untain ash 
(Sorbus aucuparia) , which he investigated, lie only in the bark and have no 
connection with the wood body; Kotschy*', on the other hand, describes 
bark tubers lo to 15 cm. large on the old trunks of the Lebanon cedar, as 
gnarly, woody excrescences, firmly fixed in the bark, which are connected 
with the mother trunk by a few vascular bundles. Masters'^ also suspects 
that some of the tubers {gnaurs or burrs) in the elm, etc., as also in many 
apple varieties, are only aggregations of adventitious buds. 

A work by Krick- reconciles the apparently contradictory theories. He 
has determined that the bark tubers (Sphaeroplasts) of the red beech de- 
velop in connection with preventitious buds, either separating from the wood 
axis of the trunk, or developing independently in the bark. In the latter 
case the tubers have a woody, cork, or phloem core but never real pith. 

The latter kind of tuber formation which takes place in the bark paren- 
chyma, outside of the primary group of phloem fibres, carries us over to the 
second group of bark tubers in which certainly no bud primordia participate. 



1 Lindley, Theory of Horticulture 198. Translated by Treviranus 1850, p 37. 

2 Loc. cit, p. 224. 

3 Scliacht, Der Baum, 1853, p. 134. 

4 Ratzeburg-, Die iStandortsgewachse und Unkrauter Deutschlands und der 
Schweiz. Berlin 1859, p. 243, Note 1. 

5 Ro.ssmassler, Versuch einer anatomischen Charakteristik des Holzkorpers 
der deutschen Waldbaume. Tharandt. Jahrb. 1847, Vol. IV, p. 208. 

6 Kotscby, Reise in den cilicischen Taurus. Gotha 1858, p. 267. 
"! Masters, Vegetable Teratolog-y 1869, p. 247. 

s Krick, Fr., tJber die Rindenknollen der Rotbuche. Bibliotheca botanica 1891 
Part 25; cit. Bot. Zeit. 1892, p. 401. 



864 

In this we have to mention first Geniet's^ investigations of tuber formation 
in Sorbus aucuparia. He found the dead tubers so loosely attached to the 
bark that they could easily be lifted out with the finger nail while the living 
ones were apparently firmly fixed in the sapwood. Nevertheless, they 
proved to be "completely separated from it and appeared as bodies possibly 
belonging in some way to the phloem because the very reddish color of their 
smooth under end corresponds to that of the phloem." Most tubers, when 
cut through, show several centres about which complete wood layers have 
developed in 13 to 15 annual layers, provided with vessels and medullary 
rays and agreeing in their cell structure with the wood of the trunk. The 
course of the wood layers was gnarly. The annual rings were almost always 
broader in the under half of the tubers toward the trunk than in the upper 
one, projecting from the trunk. It was not possible to prove any connection 
with a bud. Even when a tuber lay near a wen, no connection could be 
found with any of the many bud cones of the wen. 

Unfortunately, Gernet had no opportunity to study the initial stages of 
tuber development; the youngest stages in his material were tubercles 0.5 
mm. in size, still completely enclosed in the bark, without having caused any 
external protuberance. They lay outside the phloem fibre and were spher- 
ical or ellipsoid and showed several centres about which the wood body had 
already been deposited. This consisted of parenchymatously formed cells 
in which a differentiation of medullary ray cells became recognizable in 
longitudinal sections. The first indications of vessels may be considered to 
be represented by a few cells with large lumina but still lying above each 
other with almost horizontal, unbroken walls and containing less starch, or 
none at all. The farther all these cells lay from the centre, the more clearly 
noticeable became the lessening of their radii and the lengthening of their 
tangential axes ; their cross section approximated that of summer wood. In 
older tubercles are found at first sharply differentiated a few pitted vessels 
and a clearly recognizable central parenchymatous centre, rich in starch. 
The wood body was surrounded by a cambial zone and its own bark. In 
the upper half of the tubers, cork formation took place at times in the inner 
bark. The outer side of this newly produced cork zone was united, not 
infrequently, with the cork zone of the trunk. The part of the bark isolated 
by such a cork zone (Gernet's "cork dam") loses its starch grains, becomes 
filled with air and dies gradually so that the outer side of the tuber body 
contains dead tissue. As a rule, the appearance of these cork layers also 
introduces the death of the tuber, which occurs within the next few years. 
The under half of such diseased tubers, as well as that of perfectly healthy 
ones, retains its living bark tissue and the formation of the bark body pro- 
gresses with that of the wood body. From this we may conclude that the 
tuber grows downward and thus its upper part gradually projects above the 
surface of the bark of the trunk by rupturing it. 



1 Gernet, C. v., tjber die Rindenknollen von Sorbus aucuparia. Moskau 1S60. 



865 

Judging by this, Gernet arrives at the conclusion that, even if he did 
not know the initial stages of the tubers, he must still deny any connection 
between them and the wood body of the trunk and can consider the tubers 
to be produced neither from preventitious nor adventitious buds. 

Having investigated the tubers of apple trees, I can confirm absolutely 
this point of view. For my investigation I had at my disposal tubers vary- 
ing in size from a millet grain to a pea ; they came from the base of the trunk 
of a young apple tree, possibly eight years old. The tubers lay in the outer 
bark, from which they could be easily separated. The under side was either 
completely covered with a smooth bark (Fig. 205, / a) or showed a 
brownish, dry point, without any bark and somewhat depressed (i-k) which 
was surrounded by a green circular bark wall. 

Fig. 205, 2 gives the median cross section of the latter kind of tuber. 

In this we see a median core i2,b) consisting of two phloem fibre 
groups separated by a little parenchyma ; other tubers have only one phloem 
strand in the core, or two or three isolated cores. Around the bundle are 
deposited cells, parenchymatous in form, with slightly lignified walls and 
arranged radially. It is evident that they are formed after the manner of 
cork cells. At times only a group of thick-walled, brown parenchyma cells, 
with or without starch or phloem fibres, is found in the centre of the tuber ; 
yet this) is a more rare case. Finally, tubers are formed now and then 
with a small central cavity, filled with the brown remains of cells. 

The radially arranged, circular zone of lignified, parenchymatous cells 
passes over gradually into narrow, thick- walled, somewhat elongated wood 
parenchyma cells, horizontal or diagonal in course, between which lie scat- 
tered, short, broad vessels with simple pits (Fig. 205, 2,g'). These groups 
are already divided into numerous circles of vascular bundles by approxi- 
mately cubical medullary rays deposited in one to three rows. The 
phenomenon begins here which continues in alternative zones out to the 
periphery of the wood body, viz : that the elements of the one part of the 
bundle, which lies between two medullary rays, show a course differing from 
that in the adjacent bundle. While the cells and vessels of the one part 
seem cut crosswise (2 h"), the fibres of the adjacent part are cut longitudin- 
ally. This is found in trunks which have overgrown some constriction and 
may be explained only by the theory that the different parts of the cambium 
of the wood body, which curves about the core like a shell, are exposed 
simultaneously to different pressure and strain. Since the young tuber 
body has no exact spherical form but is only approximately round, the parts, 
which are to overgrow the corners already formed elongate more in the 
same length of time. 

The elements become narrowed, longer and thicker-walled toward the 
outside of the tuber until they have nearly the length, form and, in places, 
arrangement of the normal wood body. 

Inside the tuber, as in the wood, a differentiation of the annual rings 
into spring and summer wood is found, so that it is evident that the tuber 



866 

is a wood body, provided with the pecuUarities of the species and isolated in 
the bark ; its elements grow in all directions around one or more elongated 
or short cores. 




Fig. 205. Bark tubers from an apple trunk. 



The cambial zone {2 c), surrounding the wood, annually produces a 
new bark (2 rs) and, in injuries, heals the wounds just as in a normal trunk. 
Such an injury has taken place in Fig. 204,.? since the bark and sap wood 
have been removed from the tip of the tuber by some external influence. In 



86; 

consequence of this a normal overgrowth edge (2 u) completely covered 
with bark is produced which forms the outwardly noticeable circular wall 
about the tip of the tuber (Fig. 204, ik). 

The fact, noticeable at first, that phloem fibres are found in the centre 
of a wood body, leads to the conclusion that the tissue surrounding the 
phloem fibre groups is the place where the formation of the wood begins. 
This conclusion is still more strengthened by the structures near the tubers. 
Frequently younger phloem bundles are found here, even at times the very 
youngest ones just appearing from the cambial zone, which are surrounded 
by peculiar, radially arranged cells (Fig. 204,5). In some cases these 
plate-like cells of the "phloem circumvallation" turn blue with iodine and 
sulfuric acid; in most cases, however, they turn yellow. This shows that, 
as a fact, the tissue surrounding the phloem group tends easily to cell 
increase. 

The overgrowth of the phloem by cork tissue is in no way restricted to 
the tissues surrounding the gnarl tuber. In the trees I have investigated it 
was found in different places after many an injury. In this, however, the 
cells always have the character of cork cells and serve excellently to cut off 
a diseased phloem bundle from the healthy wood. Any one who has worked 
much with diseased trees knows how sensitive the bark cells are which have 
apparently so resistant a structure. Their brown color and the more dis- 
tinct appearance of their layers make it possible to trace the disease deeper 
into the healthy tissue than can be done in the surrounding bark parenchyma. 

The overgrowth of the phloem begins, as a rule, in the cells of the 
phloem sheath and remains limited at times to one side, or at least develops 
more vigorously on the outerside. Similar phenomena, like the overgrowth 
of the phloem bundles, are found also in some parts of the parenchyma. 
Without any reason, known as yet, the parenchyma here substitutes for the 
core a meristem zone in the bark which increases by growing around the " 
centre of fibres, thus beginning the formation of bark tubers. Such tubers 
have usually a somewhat regular structure since the course of the tissue 
elements in several annual rings keeps to the same direction. In a median 
longitudinal section which may be recognized by the fact that the medullary 
rays lie in approximately the same plane, the bent vessels are cut through 
their whole length so that they interrupt the dark, parallel wood cell zones 
as clear, concentric rings. 

The drawings (Fig. 206) made from the bark of a healthy one-year-old 
pear twig give an interesting contribution to the explanation of tuber forma- 
tion. We see in Fig. 206, i, the basal part of a very strong one-year-old pear 
shoot of which the buds (a) are set in the normal two-fifths position ; h is the 
one-sided swelling in the centre of the internode, reproduced again in cross 
section in Fig. 206, 5, cut through in the deepest part, which is turned 
toward the base of the twig, in Fig. 206, j in the median region, and in Fig. 
206, 4 in the highest zone. In Fig. 206, j, 4, 5, the same letters indicate the 
same parts ; r, the bark, g and g-, etc., the bark vascular bundles in various 



868 

stages of development. It is evident that those first formed also become 
smaller at first after entering the axis, ni is the pith ; m b, the pith bridge 
of a central leaf trace, of which the secondary bundles are unequally devel- 
oped ; ni* st, medullary rays ; hb phloem fibre groups, which compose the 
central core of the wood cord formed in the bark. In Fig. 206, 4 rt' is the 
bark killed by pressure and pressed into the trunk by the xylem strand 
formed in the axis of the branch. Fig. 206, 5 g^ indicates a xylem strand 
with the beginnings of overgrowth ; this is seen to be more strongly devel- 
oped on the outer side. Fig. 206, j ^' is a xylem strand which has not closed 
completely into a wood cylinder. Its formation took place as follows : cell 
increase began on the outer side of the phloem fibre group in the phloem 
sheath and led to the formation of vascular elements and wood cells. The 
one-sided wood body thus produced is closed by the gradual union of the 
two edges, turned to the centre and growing toward each other. Fig. 206, 
5 c' is the cambial zone of a xylem, strand already closed internally but still 
pressed into a kidney shape at the place of union. Fig. 206,2 gives a part 
of Fig. 206,5 9 somewhat magnified. 

In Fig. 206,2 is seen the complete correspondence with the centre of 
the gnarled tuber in the apple, hb is the phloem fibre group ; p, the wood 
parenchyma; g, the vessels; x, short, cross-cut wood cells; x, wood cells, 
extending horizontally from the inner convexity of the wood cord at the 
place where the two edges have united ; m represents the rows of medullary 
rays spread out like grasping arms ; c, the cambial zone surrounding the 
strand; r, the youngest bark parenchyma of the specialized zone of bark. 

The xylem strands (Fig. 206,5) are, therefore, produced' at the base of 
the swelling by an unusually abundant nutrition of the phloem sheath; 
their primordia lie at unequal heights. When enlarging, they compress at 
first the bark tissue. (Fig. 206, j) which separates them from each other and 
finally also the tissue lying above them, which separates them from the axial 
cylinder and is found later as a brown mass in the centre of the wood body 
(Fig. 206,^ rt). With their entrance into the axial cylinder, the form of 
the xylem strands in the bark is changed; the core becomes eccentric and 
finally pressed back to the tip of the wedge-shaped strand as shown in Fig. 
206,^ g, g^, g^. The change of form is, therefore, exactly the reverse of 
that undergone by the normal vascular bundle which enters the bark from 
the axial cylinder. 

Farther out the branch becomes normal^. 

The occurrence of bark-produced wood strands, therefore, explains as 
follows the production of the gnarl tuber. The mature tuber is a wood 
sphere isolated in the bark, of which the upper surface is composed of a 
cambial and bark mantle, receiving its nourishment from the surrounding 
bark tissue. According to the investigations of the above-named scientists. 



1 On the similarity of this formation of the secondary wood with that in the 
Papindaceae compare Sorauer, Die Knollenmaser der Kernobstbaume. Landwirtsch. 
Versuchsstationen 1878. 









I. 



> ■' 









^ 



-/^' 



<:f' 






-.r 







.QCICE^^^^^-^ 



r 






e?^ 






<^.^ 

-,4^ 



^ 




^•"^^r.; 







~p^^ 



Fig. 206. Production of isolated wood centres in the bark of a one year old pear 

branch. 



870 

which need repeating, the gnarl tubers, or tuber gnarls, can develop from a 
dormant bud and are, therefore, originally connected with the wood body 
of the branch. In many cases, however, they are produced as bowl-like 
wood deposits around a group of' phloem fibres, or some other bark tissue 
group without any connection with the wood cylinder or a bud primordium. 
The tuber is gradually pushed out into the outermost regions of the bark, 
which is beginning to form the cortex ; the longitudinally elongated xylem 
strands of the bark, related to the tuber formation, can press back into the 
axial body and become elements of the normal wood cylinder of a branch. 
External wounds in the tuber body are healed by overgrowth, just as in the 
normal branch and there is no reason to doubt that adventitious buds can 
develop from the overgrowth edges as well as from the normal bark of the 
tuber, as has been stated for the olive. 

Mention should be made of the fact that the large spherical swellings, 
produced on oak branches by the overgrowth of places where Loranthus 
europaeus had grown, have also been termed gnarl tubers or heads. Accord- 
ing to our division of the subject, these are not actual "gnarls" but gnarly 
overgrowth edges. 

Tine Tammes^ describes as abnormal overgrowths the peculiar cone- 
like processes on Fagus silvatic a which, usually grow broader on one side 
and overlap. Investigation shows that the stump of a branch is involved 
here, which has been closed by gnarly, hypertrophied wound edges. The 
hypertrophy has been caused by the severe pruning of the trees on account 
of which a superabundance of plastic material is deposited at the remaining 
centres of growth. 

Peters, in his observations on H elianthus anniius and Polygonum cus- 
pidatum^ gives an example of bark tubers in herbaceous plants. The tubers 
produced in the middle bark should be considered as the reaction of the 
plant to wound stimulus. A few cell groups in the bark die and dry up ; 
the cavity thus produced becomes surrounded by a cambial zone which 
forms wood on the inner side and bark tissue on the outer. 

Th. Hartig^ mentions examples of tuber formation in roots when 
describing the fact that young aspens occur in great numbers on cleared 
tracts where no seed bearing trees had stood for some time. As Th. Hartig 
explains, the little plants owe their existence to the continued growth of 
roots left from long dead and outwardly vanished frees. 

The basis of root growth in these cases is always a tuber-like woody 
thickening of a weak root strand. The tubers themselves are somewhat 
like those at the gnarly base of old oaks or lindens and those in the bark of 
the red beech ; they are the woody trunk of a dormant eye which, completely 
individualized, lives a parasitic life on the root of the parent plant "like the 
dormant eyes of the American species of pine." The aspen roots are kept 

1 Tine Tamnies, tJber eigentumlich gebildete Maserbildungen an Zweigen von 
Fagus silvatica L. Recueil des travaiix bot. Neeii. No. 1. Groningen 1904. 
-' Cit. Zeitschr. f. Pflanzenkrankh. 1905, p. 26. 
3 Loc. cit., p. 429. 



871 

alive by these tubers without any growth of the feeding root. As a rule, 
the piece of root, bearing the tuber, is found to be dead and decaying a few 
centimeters from the tuber. Andreae^ describes gnarled tubers on the roots 
of Ailanthus glandulosa; they are produced from roots and from branch 
primordia. 

In connection with this, a structure may be mentioned here which is 
often described as the Club root of beets- but has not yet been sufficiently 
explained. Usually in dry soil there appears near the crown, or a little 
farther down, a spherical swelling covered with cork, resembling the root 
body in structure but differing from it in composition because of. a greater 
water, ash and protein content. The vascular body shows that the swelling 
should be considered as the enlargement of a vascular ring of the parent 
root and may, therefore, be considered an offshoot of it probably caused by 
an excess of nitrogen after some injury^. The swelling is not parasitic but, 
because of its porous bark structure and its inert sugar content, is easily 
infested by animal and vegetable enemies. 

Leaf Injuries. 

In consideration of the fact that the results of injuries appear more 
clearly in leaves and other fleshy parts of plants, we will call attention to 
the conditions which we call wound stimulus. The first effect of the 
stimulus, which is exercised on the organ by every injury, may well consist 
in a traumatropic deposition of protoplasm in the tissue immediately adja- 
cent to the wound surface. According to Nestler's* investigations, the 
protoplasm in the uninjured cells collects on the side toward the wound and 
somewhat later the nucleus moves toward that side. This action of the 
stimulus extends a few cell rows into the healthy tissue and after about 48 
hours reaches its maximum. After this, a more or kss complete return to 
the normal condition sets in. This change in position seems to take place 
more quickly in the light than in the dark. 

In the same way, the chlorophyll apparatus often undergoes a consid- 
erable change of position-''. In many cases an increase of respiration may 
be noticed at the same time; in the fleshy parts of plants, especially, a rise 
in temperature could be proved which has been called fever reaction"'. The 
production of carbon dioxid in wounded leaves is said to be especially in- 
creased if they are poor in carbon-hydrates'. The reactions set in earlier 

1 Andreae, tjber abnorme Wurzelanschwellungen bei Ailanthus glandulosa. 
Inaugural dissertation. JErlangen 1894. 

2 Briem, H., Strohmer und Stift, Die Wurzelkropfbildung- bei der Zuckerriibe. 
Osterr. Ungar. Z. f. Zuckerindustrie 1892, Part 2. 

3 Geschwin, Le goitre de la betterave. La sucrerie indigene. Cit. Bot. Centralbl. 
f. Bakt. II, 1905, p. 486. 

4 Nestler, A., tJber die durch Wundreiz bewirkten Bewegungserscheinungen des 
Zellkerns und des Protoplasmas. S. Akad. Wien CVII, I, 1898. 

5 PfefCer, W., Pflanzenphysiologie. 2nd Ed. 1904, Vol. II, p. 819. Here also 
literature on the action of Wound Stimulus. 

6 Puchards, Herbert Maule, The evolution of heat by wounded plants. Annals 
of Bot. XI; cit. Bot. Jahresber. 1897, p. 99. 

7 Dorofejew, N., Zur Kenntnis der Atmung verletzter Blatter. Bcr. d. Deutsch. 
Bot. Ges. XX, 1902, p. 396. 



872 

or later according to the degree of injury. According to Townsend^ the 
hastening of growth becomes evident in 6 to 24 hours after slight injuries, 
while severe injuries at first cause an arrestment before the increase in rate 
begins, which, according to the plant, reaches its maximum in 12 to 96 hours 
and then gradually returns to the normal condition. Krassnosselsky- traces 
the increase of respiration to an increase of the respiratory enzyme. He 
carries out further Kovchoff's experiments which show that an increase in 
the whole amount of protein and especially of the nucleo-proteids takes 
place after an injury and then proves (in injured bulbs) that the sap con- 
tains more oxydases than does that from uninjured specimens. The same 
is true of potatoes. 

The subsequent reactions of leaves after injury vary greatly according 
to the species of the plant, the age of the leaf and the time of injury. We 




n{f 



P'ig. 207. Injury to a leaf of Leucojum vernum, which is being- closed by callus 

formation. (After Frank.) 

will content ourselves with discussing the two extremes, viz : the reaction of 
a tough leathery leaf and that of a fleshy one. In the former, Prunus 
Laurocerasiis represents a case in which a sloughing process of the injured 
cell group is connected with the injury as has already been mentioned under 
the results of spraying with copper. According to Blackman^ and Matthaei* 
either the injured cells alone die, or those immediately adjoining them, 
according to the part of the leaf injured. A brown zone with a lighter 
colored centre is produced around the wound. The epidermis splits in this 
hyaline region and colorless, very thin-walled, cells grow out of the adjoin- 

1 Townsend, C. D., The correlation of growth under the influence of injuries; cit. 
Bot. Jahresber. 1897, I, p. 98. 

2 Krassnosselsky, Bildung der Atmungsenzyme in verletzten Pflanzen. Ber. d. 
Deutsch. Bot. Ges. 1905, Vol. XXIII, p. 143. 

3 Ber. d. Deutsch. Bot. Ges. 1903, p. 165. 

4 Blackman, F. F., and Matthaei, G. L., On the reaction of leaves to traumatic 
stimulation. Ann. Bot. XV; cit. Zeitschr. f. Pfianzenkrankh. 1902, p. 61. 



873 

ing mesophyll. These form a cuticle and thus represent a complete cover- 
ing of the wounded leaf surface. When this covering is complete, the dead 
tissue is thrown off. In this the pressure of moist air is taken for granted. 
In other cases a normal periderm is formed from several cell layers which 
suffices as a protection for the healthy leaf tissue. 

The second case of the healing of leaf injuries, viz : by callus formation, 
is explained by the accompanying figure. It is the cut wound from a cut 
on Leucojum vernum. The wound lay in the open space between the two 
tissues of lamellae / and f ;vv v v are the edges of the wound with the dead 
pieces of tissue. The wound cavity is now filled by the callus cells devel- 
oping by elongation from the fresh tissue, which lack chlorophyll and have 
suberized walls. The normal condition of the leaf is represented at the 
left side of the figure where i i indicates a large air chamber; the tissue sur- 
rounding it has not been changed by wound stimulus, o is the upper and u 
the under side of the leaf. Many fleshy leaves react according to this 
scheme, but their processes of healing vary greatly, depending on the subse- 
quent participation of the process of cork formation. Complete union of 
the edges of the wound can also take place, as may be observed, for example, 
in the cut surfaces of fleshy roots and tubers^. The union is sometimes the 
result of organic coalescence, sometimes only a cementing of the surfaces 
since the cut cells are changed into a gum-like mass by the swelling and 
disintegration of their walls. 

The leaf can under certain circumstances reproduce the part arti- 
ficially removed (regeneration, according to Kiister) or form a compen- 
sating organ (restitution-) according to the specific character of the leaf, 
its youth and its distance from the reserve-substance containers. 

Frequently whole leaves, or pieces of leaves, removed from the plant, 
can form new roots and aerial axes. This capacity is utilized for 

Leaf Cuttings. 

The best known and most frequent use of leaf propagation is found 
in begonia culture. According to Hansen'^, in the various varieties of 
Begonia Rex wounds produced by slashing the nerves of the leaf lying flat 
on the soil are closed at once by callus. In this way a tuberous tissue is 
formed on the mother leaf from which tissue, or that immediately sur- 
rounding it, roots develop ; later, sprouts are formed from the same tissue, 
which, however, do not develop their own roots but are nourished by the 
above-mentioned roots of the callus. Sprouts develop there from one or a 
few cells of the epidermis near the cut rib, sometimes nearer, sometimes 
farther from the wound. In such cells, a horizontal partition wall is pro- 

1 Fig-dor, Wilhelm, Studien iiber die Erscheinung- der Verwachsung- im Planzen- 
reiche. Sitzungsber. d. Akad. d. Wissensch. Wien; cit. Bot. Zeit. 1891, No. 23. 

- Pigdor, Wilhelm, tjber Regeneration der Blattspreite von Scolopendrium. 
Bericht d. Deutsch. Bot. Ges. 1906, Vol. XXIV, Part 1. — Figdor, Wilhelm, tJber Resti- 
tution-serscheinungen an Blattern von Gesneriaceen. Jahrb. f. wiss. Bot. 1907, Vol. 
XLIV. Part 1. 

. 3 Hansen, Ad., Vorlauflge Mitteilung. Flora 1879, p. 254. 



874 

duced at first and gradually by further division the meristem of the young 
sprout from which a roll differentiates as the first leaf. 

The roots are formed laterally from a few cells lying near the cambial 
zone of the vascular bundle. These, therefore, "endogenously" formed 
roots soon rupture the overlying tissue. As Fr. Regel^ states, the roots of 
begonia branch cuttings can also arise from the inter-fascicular cambium. 
This author, who has investigated several other begonias beside Begonia 
Rex with rhizome-like, recumbent petioles, as, for example, Begonia im- 
perialis and B. xanthina, mentions that the formation of buds also takes 
place on the leaf blade near the incisions. After the epidermal cells have 
divided, the underlying collenchyma and the ground tissue are also drawn 
into the new formation and help in producing the mound of cicatrization 
tissue at the place cut. This tissue differs from that of branch cuttings 
only in the fact that here the epidermis participates in the cell increase. 

This activity of the epidermis can become of very especial physiological 
importance immediately after the cut is made since a few of the upper epi- 
dermal cells near the wound elongate like hairs (pseudo-root hairs) and, 
without doubt, develop a root-like activity until the true roots are formed. 

In the adjoining Fig. 208 are shown the new structures on the cut sur- 
face of a larger leaf rib in a hybrid Rex begonia. A indicates the old part 
of the leaf, B the new structures. At first an abundant callus tissue (c) 
develops from the cut and soon shows an apical growth of its cell rows but 
indicates by the parallel edges of the cork cells that it is in the process of 
transition to overgrowth edges. The endogenously formed new root (w) 
breaks out on the under side of the boundary between the callus and the old 
leaf tissue, while on the upper side, two new bud primordia have already 
been formed. The younger one of these shows at d the meristematic tissue 
of the young bud with the epidermis {e). This meristematic tissue is pro- 
duced by the division of the original epidermal cells and the sub-epidermal 
tissue. The second bud has been formed earlier at a point lying farther 
away from the cut and already is further developed. The real bud cone {d) 
is already overgrown by a more convex leaf primordium {hi) into which 
extend young spiral vessels (/). The vascular bundle ring of the older 
part' of the leaf is indicated at g, while t indicates the vascular bundles 
extending into the new root. 

Kny- noted that the vascular bundles had become larger on the petioles 

^of Begonia Rex, on which adventitious sprouts had been produced. The 

cambium, like the adjacent ground tissue, had continued its cell division, 

whereby the new walls between the adjacent bundles were predominantly 

parallel to the outer surface of the petioles. Kny regarded this as the 



1 Reg-el, Fr., Die Vermeliruns: der Begoniaceen aus ihren Blattern usw. 
Jena'ische Zeitschr. f. Naturwiss. 1S76, p. 477; cit. Bot. Jahresber. 1876, p. 423, 439, 
452, etc. 

2 Kny, L... Tiber die Einschaltung- des Blattes in das Verzweig-ungssystem der 
Pflanze. From "Naturw. Wochenschrift" 1904; cit. in Bot. Centralbl. (Lotsy) 1904, 
No. 50, p. 612. 



875 

beginnitig of an inter-fascictilar cambium which, developing further, would 
have closed the peripheral bundles into a circle. ■ 

From the many observations already made on leaf cuttings, the assump- 
tion is justifiable that the processes described above for begonia may occur 
also in many other leaf cuttings. The foliage shoots develop from more or 
less superficial cells ; the root primordia are produced from the cells border- 
ing the cambial zone and either break through the old tissue of the cuttings 
or arise from the cicatrization tissue of the wound. Variations in the 
different genera are usually unimportant and differences of opinion among 




Fig. 208. Leaf catting from a hybrid form of Begonia Rex. 



the various authors are often explained by the fact that individuals of the 
same plant species under different conditions and of different age do not 
always show exactly the same processes. Beinling's^ investigations, for 
example, prove that the genus Peperomia does not form any callus but 
covers the cut surface with wound cork. He also found buds produced 
from the ground parenchyma of the petiole, or the blade, but not from the 
epidermis and always independent of the vascular bundle. On the other 



1 Beinling, E., Untersuchungen iiber die Entstehung der adventiven Wurzeln 
und Laubknospen an Blattstecklingen von Peperomia. Inauguraldissertation. 
Breslau 1878, p. 23. 



876 

hand, Hansen^ describes in detail the processes of root and sprout formation 
in Achimenes and Peperomia from the callus. In this only the first adven- 
titious roots are produced from the already existing tissue elements. After 
the callus tissue had increased for some time numerous pro-cambial strands 
showed themselves in the callus, extending in all directions toward the 
surface. Their cells soon changed into tracheae ; so that "callus"- is pro- 
vided with a branched system of vascular bundles. Soon the peripheral 
cells of this tissue appear to be abundantly filled with protoplasm ; they 
divide and produce a meristem which differentiates, as do the normal vege- 
tative points, and soon an epidermis becomes very distinct. 

In the leaf cuttings of the monocotyledons, the processes of bud forma- 
tion are the same as those in dicotyledons. Magnus'^ describes bulb cuttings 
of hyacinths. Numerous adventitious buds are formed on the ventral side 
of the cut surface which, in case the bulb scale was still young, are produced 
from an epidermal cell or in older scale pieces from the underlying paren- 
chyma. At first tender knobs of tissue are formed from the dividing tissue 
cells which continue growth at 'the apex in diverging cell rows ; dividing 
dichotomously. It is, therefore, actual callus. On further developed knobs, 
a circular wall appears, developing into the first sheath-like scale of the 
adventitious bud, while the enclosed apical cell shows growth in diverging 
cell rows. On the bulb scales of Lilium Tigrinum and L. Auratum the buds 
are also formed on the outer edge of the inner side. The rootlets, arising 
on the outer side from the phloem region of the vascular bundles, live only 
a short time since the young plant at once forms independent roots. 

The processes of bud formation in leaf cuttings do not differ essentially 
from the voluntary production of the buds on uninjured leaves on the plant. 
Numerous examples of these are well known*. They have been observed 
in mosses and ferns^, in lilies and other monocotyledons, most numerously 
in dicotyledons. Beijerinck formed as a law for the latter, that the vascular 
bundles of the leaf have an influence on the primordia of the adventitious 



1 Hansen, Ad., tiber Adventivbildung-en. Sitzungsber. d. phys.-med. Soc. zu 
Erlang-en vom 14 Juni, 18S0; cit. Bot. Centralbl. 1880, p. 1001. 

~ Opportunity is here given to call attention to the fact that the authors include 
two different conditions under the name "Callus." 

They call tissue callus which is produced from* the first cell divisions, and has 
for some time an arrangement in rows; it continues growth, especially at the apex 
of the cell rows, and lacks all differentiation. 

In the second place, however, the authors, in accordance with general usage, 
understand by callus the structure differentiated from the callus by the production 
of a cork zone, the formation of an inner meristem centre and the separation of a 
ground tissue. This structure has already become similar to the tissue from the 
wound in which it is produced. However, the juvenile conditions, distinguished by 
apical growth, should be distinguished from these mature conditions and I propose, 
on this account, to apply the term "callus" only to the first structures, while the 
later stages can be known as "cicatrization tissue." 

3 Magnus, Hyacinthenblatter als Stecklinge. Sitzungsber. d. Ges. naturforsch. 
Freunde vom 16 Juli, 1878; cit. Bot. Zeit. 1878. p. 765. 

* Beijerinck, M. W., Over het onstaan van Knoppen en wortels uit bladen. 
Nederl. Kruidkund. Archief. Se'rie II, Deel III, p. 43S-493; cit. Bot. Centralbl. 1883, 
No. 17, p. 112. 

5 Farlow, Bot. Zeit. 1874, p. 180.— Cramer, Geschlechtslose Vermehrung des 
Farnprothalliums, namentlich durch Gemmen resp. Konidien. Denkschr. d. Schweiz. 
Naturforsch. Ges. XXVIII, 1880. 



877 

organs. The adventitious buds are always found on the upper surface 
where the woody part of the vascular bundles is turned toward the upper 
side of the leaf ; they are produced in the axes of the ribs and are usually 
more strongly developed the thicker the vascular bundles. The roots are 
produced from the phloem side of the vascular bundles. 

RegeP enumerates the plants on which buds of leaf origin have been 
observed. A few examples may be named here since the buds develop 
their own roots after having been carefully removed from the leaf and, 
therefore, are of importance in propagation. Besides the well known 
Bryophyllum calycinum, which Berge- studied and on which incisions 
between two serrations of the leaf develop a meristematic tissue in an early 
stage and from this meristem buds, the following species are noteworthy: 
Hyacinthus Pauzolsii, Fritillaria imperialis, Ornithogalum thyrsodies, 
Drimia, Malaxis, Cardamine, Nasturtium, Brassica oleracea, Ranunculus 
hulhosus, Chelidonium majus, Levisticum offic, Ultricularia, Begonia quad- 
ri-color, B. phyllo maniac a^. Hansen'* mentions also Hippuris, Elodea 
canadensis and other water marsh plants. Caspary'^ mentions Nymphaea 
micrantha and its hybrids. He also cites examples in which an inflorescence 
developed instead of a leaf. In this way the upper side of the petiole of a 
cucumber (Cucumis sativus) was covered with more than 120 staminate 
blossoms without a single vegetable leaf. 

The success of propagation by leaf cuttings depends upon the indi- 
viduality of the leaf as well as upon the plant species. Very young leaves 
must be excluded because of the immaturity of their tissue systems ; very 
old ones because of their scanty life energy and the 'ripeness of their chloro- 
phyll apparatus. 

According to Lindemuth's" observations, in genera where the leaves can 
be used as cuttings, the plants thus produced are on an average stronger 
than those from wood cuttings. As soon as a leaf has developed a few 
roots, it may be considered a new individual, even when it is not able to 
produce shoots. This arises from the capacity of such leaves to live longer 
than unrooted ones and Goebel" could also prove an increased growth in 
thickness (in Bryophyllum). Lindemuth also observed, in a begonia, that 
a flower shoot can be formed instead of foliage shoots in leaf cuttings. This 
circumstance might indicate that the leaves furnish different products of 
assimilation at different ages and places on the axis. Usually the assimilates 
capacitate the bud, produced on the leaf cutting, to form only foliage shoots. 



1 Loc. cit, p. 452. 

2 Beitrag'e zur Entwicklungsg-eschichte von Bryophyllum calycinum. Ziirich 
1877; cit. Bot. Jahresber. IV, p. 423. 

•■' Mohl, tjber die Cambiumschicht des Stammes der Phanerogamen und ihr 
Verhaltnis ziim Dickenwachstum desselben. Bot. Zeit. 1858, p. 196. 

4 Loc. cit., p. 1002. 

5 Caspary, Bliitensprosse auf Blattern. Schriften d. phys.-okonom. Gesellsch. 
XV, 1874, p. 99. 

6 Lindemuth, H., Weitere Mitteilungen iiber regenerative Wurzel^ und Spross- 
bildung auf Laubblattern (Blattstecklinge). Gartenflora 1903, p. 619. 

7 Flora 1903, p. 133. 



878 

Often, however, they are of a concentration which makes possible the 
formation of flower buds. 

In general practice at times the petiole is used for propagation instead 
of the leaf, in case the leaf itself is too tender. A recent example is the 
propagation of the cultivated forms of Begonia semperflorens, which is sold 
under the name of Gloire de Lorraine and greatly prized as a winter 
bloomer ^ In February the most vigorous leaves are cut off close to the 
stem and the petiole set i to 2 cm. deep in sand and peat mold. At a tem- 
perature of 18 to 22 degrees C. these petioles form root balls as large as 
walnuts. Other begonias as, for example, the Rex forms set roots from 
their petioles but almost never develop strong buds. The petioles of cab- 
bage, celery and other fleshy plants behave similarly. 

The flower stems of Primula sinensis may be used successfully as cut- 
tings. Cramer- used flowers with the leaf-like perianth of this plant, in 
which buds were produced in the axes of the reproductive leaves. A case, 
which Baillon observed, showed that the fruit could also be used as cuttings ; 
in this, roots developed from the fruit of a cactus''. The same author also 
cut in two just>above the base the ovary of Jussieus salicifolia. This bore 
two leaflets near the centre, and was cut during and after blossoming in 
such a way that the ovules could be seen ; these cuttings were set in a pot. 
Three weeks later the well-rooted cuttings were transplanted. A small 
branch with scales appeared in the angle of the carpels. The upper part of 
the blossom died and a circular scar was formed*. Irmisch describes root 
formation on the cotyledons of Biinium crcticum and Carum Bulbocosia- 
nunv'. I have seen root formation in the broken-off cotyledons of beans 
(Phaseolus vulgaris). Carriere found roots on the fruits of Lilium lanci- 
foliuni. Beinling" found flower stems of Echeveria which, in moist sand, 
had grown roots. 

Hildebrand' describes a fruit of Opuntia Ficus indica out of which a 
second had sprouted ; both fruits after separation from the plant developed 
leaf sprouts. The same thing happened with blossom buds of Opuntia 
Raffinesquiana. Therefore, each plant organ may be capable of developing 
leaf sprouts b) the formation of adventitious buds, provided first that it 
contains enough reserve substances to live for some time separated from the 
parent plant, and secondly that the external conditions are favorable. A 
summary by Magnus** gives further details together with the theories of 
Klebs, Goebel and others. , 



1 Kirst, Vermehrung' der Begonie "Gloii^e de Lorraine." Prakt. Ratgeber im 
Obst- u. Gartenbau 1906, No. 5. 

2 Bildungsabweichungen, p. 37. 

3 Vegetable Teratologie, p. 160. 

4 Bot. Zeit. 1865, p. 527, from Adansonia, Vol. I, p. 181. 

5 Flora 1858, p. 32, 42. 

fi Beinling, Untersuchungen iiber die Entstehung der adventiven Wurzeln und 
Laubknospen an Blattstecklingen von Peperomia. Inaug.-Diss. Breslau 1878. 

7 Hildebrand, F., tjber Bildung von Laubsprossen aus Bllitensprossen von 
Opuntia. Ber. d. Deutsch. Bot. Ges. 1888, Vol. VI, p. 109. 

8 Magnus, Werner, Regenerationserscheinungen bei Pflanzen. Naturwissensch. 
Wochenschrift 1906, No. 40. 



8/9 
Injury to the Foliage. 

The results of partial or entire defoliation must naturally become 
apparent in the amount of dry substance produced. , The effect varies 
according to the amount and age of the leaves removed and also the possi- 
bility of compensation for the lack of foliage by the existing buds and the 
amount of reserve substances necessary for their unfolding stored in the 
axis. 

The annual reports on forestry give sufficient examples for forest 
trees. It is not necessary to go further into this subject here since each 
separate case must be judged for itself. In the numerous injuries due to 
caterpillars, for example, the amount of injury depends upon the time and 
duration of the eating. Reference should be made, in this connection, to 
Ratzeburg\ He describes, in detail, the influence of defoliation on the 
annual ring formation of spruces and pines and treats later of deciduous 
trees-. Cieslar's'* experiments show that the anatomical structure of a 
wood ring, produced after extensive defoliation, was changed (it became 
much more tender). Under certain circumstances the vessels can be entirely 
lacking* in wood produced after defoliation. Hartig-"' had already proved 
that a decrease in number of the vessels goes hand in hand with the decrease 
of foliage. Kny" had already touched on the subject that under certain cir- 
cumstances double annual rings can be produced. Wieler' showed by 
experiments that the boundaries between spring and summer wood can be 
entirely effaced by changes in nourishment. 

Such effects can also occur in fruit trees and often manifest themselves 
in the yield. In only a few cases can a partial defoliation prove to be advis- 
able agriculturally as, for example, in grapevines, if they constantly produce 
new foliage shoots which use up the supply of nutrition necessary for the 
maturing of the grapes. 

Among annual and biennial cultivated plants, beets come especially 
under consideration because, in years when fodder is scarce, the older leaves 
are broken off in the course of the summer and used to feed the cattle. An 
example from Bohemia'* proves that the root body is thereby forced to form 
more new foliage than it would otherwise and that the storage of reserve 
substances suffers from this. It was found here that, after defoliation, not 
only did the beet root remain smaller but the sugar content was about lo 



1 Ratzeburg-, Waldverderbnis, I, p. 160, 234, etc. 

2 Loc. cit. II, p. 154, 190, 233. 

3 Cieslar, A., tjber den Einfluss verschiedenartig-er Entnadelung- auf Grosse und 
Form des Zuwachses der Schwarzfohre. Cit. Just's Jahresber. 1900, II, p. 278. 

4 Lutz, K. G., Beitrage zur Physiologie der Holzgewachse. Ber. D. Bot. Ges. 
1895, p. 185. 

•"> Hartig-, R., tJber Dickenwachstum und Jahrringbildung. Cit. Zeitschr f. 
Pflanzenkr. 1892, p. 292. 

« Verliandl. d. Bot. V. d. Prov. Brandenburg- 1879. 

7 Wieler, A., tJber Beziehungen zwischen dem sekvmdaren Dickenwachstum und 
den Ernahrungsverhaltnissen der Baume. Tharander forstl. Jahrb. 1892, V. 42. 

8 Blatter f. Zuckerriibenbau. 1905, No. 20. 



88o 

per cent, less than in the undisturbed beets. Aderhold's^ experiments with 
roots and grain gave similar results. It was found in grain that the length 
of the heads was strongly affected, irrespective of the reduction of the whole 
harvest. 

Nevertheless, one's fears should not carry one too far, nor should slight 
losses of leaf substances be considered of too great importance as has 
recently been estimated by many pathologists in judging the injury due to 
fungi. It must not be forgotten that the parts of still vigorously growing 
leaves, which have lost some of their lamina, are excited to increased effort, 
as I have proved experimentally-. Boirivant'' found, in fact, that after the 
removal of leaf blades the petioles and stems participate to a greater degree 
than usual in the assimilation and that their parenchymatous tissue can 
begin to elongate and increase. 



1 Aderhold, R., tjber die durch teilweise Zerstorung- des Blattwerkes der Pflanze 
zug-efiigten Schaden. Prakt. Blatter f. Pflanzenbau u. Pflanzenschutz. Ill Jahrg-. 
1905, Part 2. 

2 Sorauer, P. Studien liber Verdunstung. Forsch. a. d. Gebiete der Agrikultur- 
physik. Vol. Ill, Part 4-5, p. 109. 

3 Boirivant, A., Sur les tissu assimilateur des tiges privees de feuilles. Just's 
Bot. Jahresb. 1898, II, p. 231. 



SUPPLEMENT. 



Page 307. New investigations on Chlorosis have been published by 
Molz (Die Chlorose der Reben, Jena 1907, G. Fischer). In confirmation of 
the theory, which we have expressed, a lack of oxygen for the roots may 
actually be considered as the cause. On this account low positions, where 
water flowing from higher ground can collect, are the most dangerous. In 
heavy soils the development of the root system suffers from this. Lime 
itself cannot produce chlorosis but soils rich in lime cause especially the 
death of the roots, since they are often very fine grained and can produce an 
alkaline reaction. Therefore, we may speak of a calcium chlorosis. Con- 
tinued drought, as well as cold, can also produce chlorosis. Worth consid- 
eration is Molz's theory that the weak constitution of a chlorotic plant can 
be carried over by the wood used for propagation. The disease can either 
be inherent in the cuttings from the beginning, or "certain disadvantageous 
circumstances from outside, resulting from an inherited, strong predisposi- 
tion, can cause the production of the icteric phenomenon and its results." 
A permanent cure cannot be brought about hy Jron sulfate. At best only 
the symptoms will be removed and it is probable that the greening of the 
leaves is not caused by the iron but by the sulfuric acid. 

Page 335. Molz studied dropsy in grape cuttings (Bericht der Kgl. 
Lehranstalt zu Geisenheim a. Rhein, 1906). The cuttings had stood for 
some time in damp soil. They were swollen up like clubs in different places, 
thus splitting lengthwise the outermost tissue layers. A white, spongy tissue 
became visible in the gaping wound, which consisted of hypertrophied bark 
cells. Molz considers the disease, which is not uncommon in moist vine- 
yards, to be identical with that in Rihes aurcum described by Sorauer. 

Page 345. Black specks are found in the one-year-old shoots of Vitis 
vinifera and appear somewhat raised. Molz (Centralblatt f. Bakt. II, Vol. 
XX, 1908, Nos. 8 und 9) describes these as small, round knobs of a blunt, 
conical form ("bark warts"), which may be considered as a compensation 
for the lenticles not found in Vitis vinifera. Each one has a stoma on its 
tip which dries up rather early. This drying extends to the neighboring cell 
groups and advances until halted by the formation of a protecting cork 
layer. The stronger and better nourished the tissue is the more quickly the 



882 

protecting cork is produced. Poorly nourished shoots produce no protect- 
ing cork and on this account bear especially large and numerous bark warts. 
These black specks, therefore, furnish a standard for judging the degree of 
maturity of the wood and the health of the vine. The more numerous and 
the larger they are, the less mature in general is the wood. 

Page 378. In Geisenheim, Julie Jager observed a wen formation of 
the apple tree (Zeitschr. f. Pflanzenkrankh. 1908). The cause has not been 
sufficiently determined, but is probably to be found in some disturbance of 
nutrition, which manifests itself in the widening of the medullary rays. 
Some medullary rays in their primordia show a greater cell increase and 
widening of the individual cells. The process is connected with the forma- 
tion of gnarl spikes from the medullary excrescences in Ribes nigrum and 
Pirus malus chinensis, which we have described. 

Pages 391 and 395. The iron spotted condition of potatoes was unusu- 
ally wide-spread in the wet year of 1907 and connected with it appeared a 
yellow to brown discoloration in the vascular bundle ring. This discolor- 
ation, in common with a frequent diseasing of the stem end, in which at 
times a Fusarium was concerned, has influenced Appel to explain the 
so-called leaf roll disease, a form of the curling disease, as a fungus epi- 
demic. Appel maintains that the Fusarium, found at the stem end, grew 
during the winter through the vascular bundle ring into the eyes of the 
tuber and caused the following year an increased occurrence of the disease 
and a gradual destruction of the potatoes. The same theory has been 
advanced by Reinke and HaUier, only they have made another fungus 
responsible for it. Sorauer proves (Internationaler phytopathol. Dienst, 
Stiick 2, 1908) that the Fusarium, to be sure, may be found frequently but 
that other slime fungi appear just as often; that all fungi could never be 
observed to be growing in the vascular bundle ring of the tuber up to the 
eyes. It is not a question of a fungous disease and its continuance through 
the tubers into the following year. The phenomena of discoloration in the 
tuber may rather be explained by the increase of the enzymes which Prof. 
Griiss has proved to have accumulated especially about the stem end. Con- 
sequently, a relatively larger amount of sugar would be present, which 
would form an especially favorable substratum, for numerous micro- 
organisms. 

Page 496. The influence of electricity on plant growth was tested at 
the Hatch Experiment Station of the Massachusetts Agricultural College 
(cit. Z. f. Pflanzenkrankh. 1908). Raphanus sativus was used as the experi- 
mental plant. It showed a hastening of the rate of growth and an increase 
in weight of foliage and roots ; the leaves, however, were a lighter green and 
were inclined to leaf blight. The electric stimulus seems to act on the 
organs in the same way as does a lack of light. 

Gassner (Berichte d. D. Bot. Ges., 1907, Part i) can confirm the results 
of Lowenherz's experiments mentioned in the text. The curvature produced 



883 

by the action of the current, which could be observed in all plants, did not 
always remain the same. At times it was toward the negative pole; in 
other cases, toward the positive pole. 

In opposition to the cultural experiments with barley, published earlier 
by Lowenherz and confirmed later by Gassner, which prove an injurious 
effect of the electric current, the first pamed author now reports favorable 
results (Z. f. Pflanzenkrankh. 1908, Part i). With a weaker current he 
found a hastening of the growth of a seedling; the injurious action began 
only with an increase of the current. 

Page 524. In the reports of the Hatch Experiment Station of the 
Massachusetts Agricultural College (cit. Z. f. Pflanzenkrankh. 1908) may 
be found observations on the leaf blight of conifers and other evergreen 
trees as the result of winter and spring frosts. The trees show the blight 
usually only on one side, which corresponds to the prevailing direction of 
the wind. If dry winds blow with a high temperature at a time when the 
soil is still frozen, the plants cannot find sufficient compensation in the 
frozen soil for the increased transpiration and the leaves dry up. This is 
the same theory which found expression earlier as explanation for the drop- 
ping of pine needles. The native conifers suffered less, in case they did not 
stand on unfavorable soil, when compared with the imported varieties of 
Picea, Abies, Juniperus, Taxus, Buxus, etc. 

Page 675. According to Stocklasa's investigations, Ueber die glykoly- 
tischen Enzyme in Pfianzenorganismus, Z. f. physiol. Chemie, Vols. 50 and 
51, 1907, the anaerobic respiration is an alcoholic fermentation in which a 
certain amount of lactic acid has formed together with alcohol and carbon 
dioxid. This holds good also for frozen organs (beets, potatoes, etc.). 
Zymases and lactacidases are, therefore, not destroyed by the freezing. 
Lactic acid, alcohol, carbon dioxid, acetic and formic acid are also formed 
by enzymes in living plant and animal cells. The decomposition of the 
hexoses by glycolytic enzymes is normally completed without the cooper- 
ation of bacteria. In the precipitates procured from pure plant juices by 
absolute alcohol and ether, the author found fermentation enzymes which 
produced a lactic acid and alcohol f erm.entation in the glycose solution ; in 
this process with easy access of oxygen definite amounts of acetic and 
formic acid are always formed. 

Page 677. Fallada's investigations (Oesterr. Ungar. Zeitschr. f. 
Zucherindustrie u. Landw. Part V, 1907) on the white leaf conditions of 
beets favor the theory that the white parts of the leaf remain in a younger 
developmental stage and with a scantier cell content and are more suscep- 
tible to the influence of light and heat than are the green organs. The 
etiolated leaves had a greater water content; the smaller amount of organic 
substances gave a relative increase of protein especially of the non-albu- 
minous nitrogen compounds. The potassium and phosphoric content was 
greater; the calcium and silicic acid content was smaller. 



884 

Page 717. For the diseases of the horseradish, we have referred to 
our detailed article in the Zeitschrift fiir Pflanzenkrankheiten, 1899, p. 132. 
It is stated there, "The forms of disease mentioned appear to me on this 
account only as a great increase of a wide-spread tendency to gummy 
degeneration . . . because in the production of the masses filling the 
vessels the liquification of the secon.dary membranes cooperates in certain 
cases." This theory has been shared recently by A. Schleyer (Ddr Anbau 
des Merrettichs usw. cit. Biedermanns Zentralbl. f. Agrik., Part 8, 1908). 
He says, "In my opinion, the turning black is conditioned by the fact that 
the Pentosane and the sugar in the horseradish degenerates into gum." 
Experiments also confirm the theory that lime should be used as a remedy 
(since humic acid is often present in the soil). When the plants v/ere 
cultivated in nutrient solutions, some of which were made up with calcium, 
others without it, the gummy degeneration of "the sugar" could be proved 
very soon in the plants which did not have calcium. 

Page 718. The subject of the injuries due to the gases of smoke and 
other industrial waste substances is beginning to be separated as a special 
branch of general pathology and is represented by a special publication. 
Since 1908, there has existed the "Sammlung von Abhandlungen iiber 
Abgase und Rauchschaden" edited by Prof. Dr. Wislicenus, who has already 
given in the first part a comprehensive description "Ueber die Grundlagen 
technischer und gesetzlicher Massnahmen gegen Rauchschaden." 

Recent investigations by Haselhoff (Z. f. Pflanzenkrankh. 1908) treat 
of the action of sulfurous acid on soil. The experiments show that vege- 
tation is not injured if the soil contains such amounts of decomposable 
bases (especially calcium) that the sulfuric acid, formed from the supplied 
acid, is combined. The case described by Wieler of soil impoverishment in 
the presence of free acids in the soil may be found very rarely (perhaps in 
forest soils). If, on the other hand, sulfurous acid is introduced into the 
soil during the growth of the plants so that it shows an acid condition, dis- 
turbances in growth become clearly noticeable. In soils containing copper, 
the copper is carried over into easily soluble compounds of the sulfurous 
acid and this dissolved copper can then become injurious to vegetation. But 
even here calcium carbonate helps since it arrests the dissolving action of 
the acid. 

Page 761. The occurrence of a disadvantageous effect of Bordeaux 
solution on the yield, which we first observed, has been confirmed by recent 
experiments of v. Kirchner (Z. f. Pfiankrank., Part II, 1908). The author 
takes the older literature also into consideration. Probably the shading 
action of the solution should be made responsible for the lessened yield. 
This would explain also the rapid turning green of leaves with strong 
illumination. The greater amount of starch is not to be ascribed to 
increased assimulation but to a decreased removal of the assimilates. 



885 

Page 765. Kelhofer (Internat. phytopath. Dinest, 1908, Part 3) has 
reported some points in regard to the making of Bordeaux Mixture. The 
effectiveness of the mixture depends not only on the quality of the materials 
used but also on the proportionate amounts of the two elements and on the 
method of preparation. 

In regard to the proportionate amounts, it should be emphasized that 
the copper precipitate loses its physical properties the more quickly and the 
danger of washing away by rain is the greater the more calcium is used in 
preparing the solution. According to Kelhofer's experiments, it is further 
desirable that the copper vitriol solution and the lime milk are mixed when 
cool and in the most dilute condition possible and, on this account, the 
copper solution must be poured slowly into the lime milk ; otherwise the 
precipitate assumes a powdery form which conglobates. Although the 
addition of sugar is to be recommended in general, care must be taken not 
to use too large amounts since the copper solution thereby may be more 
easily washed away. At any rate the amount of sugar necessary to make 
the mixture keep depends upon the amount of calcium, inasmuch as solu- 
tions prepared with a good deal of calcium need more sugar. Thus, for 
example, when using i, 2 and 3 kg. calcium, to 2 kg. vitriol to each 100 liters 
of water, 20, 30 or 40 gr. of sugar have been found necessary in order to 
protect the copper precipitate permanently from decomposition, i. e. for at 
least a year. In common usage, where, as a rule, plenty of calcium is used, 
it is advisable to take on an average 50 gr. sugar for each hektoliter. With 
this addition the whole amount of Bordeaux mixture needed can be pre- 
pared at the same time in the spring at the beginning of the season; the 
mixture will then keep through the summer. 

Page /"/2. The investigations of Rudolph Friedrich (Ueber die Stoff- 
wechselvorg^ange der Verletzung von Pflanzen. Centralbl. f. Bakteriologie, 
etc. II, Vol. XXI, p. 330) have confirmed the observations of Zaleski and 
Hettinger that an increase of protein takes place at the zvounded place. 
Besides this, however, Friedrich found that in the storage organs beneath 
the soil, as well as in the fruits and leaves, a decrease of carbo-hydrates 
and an increase of acidity (with the exception of bulbs) sets in as a com- 
mon, secondary phenomenon of the injury. If, with Ad. Mayer, the acids 
are considered as the products of oxidation of the sugars, then the increased 
acidity is explained by the more active respiratory need of the injured 
organ. The decrease of carbo-hydrates will be explained partially by the 
fact that they are used for protein synthesis. A corresponding decrease of 
amids or the amido acids may be considered as further reactions to trau- 
matic stimulus. These substances are used in the construction of the protein 
molecule. In the potato the smallest starch grains are used up and intro- 
duce the formation of sugar. 

Page 787. Hedrick, Taylor and Wellington made girdling experi- 
ments on tomatoes and chrysanthemums (Bulletin 288 of the Agriculture 



886 

Experiment Station at Geneva). No beneficial effects could be determined. 
On the contrary, the plants were very evidently injured. Knobby swellings 
were formed on the axes ; the leaves became sickly and the root system 
less developed. 

A confirmation of my personal studies on the processes after girdling 
may be found in Krieg's contributions on callus and wound wood formation 
in girdled branches and their histological changes (Beitrage zur Kallus- und 
Wundholzbildung geringelter Zweige und deren histologische Veranderun- 
gen. Wiirzburg 1908, Nubers Verb). The observations on Vitis are new 
in that the formation of new structures as a result of girdling were proved 
in the pith, although the pith had not been injured at all. This fact is 
important because it shows that the wound stimulus, or the changes in tissue 
tension setting in after each injury, manifests itself in regions far distant 
from the wound surface and separated from it by firm wood zones. This 
makes better understandable the changes in the pith body due to frost 
injuries in which the wood ring shows no disturbances of any kind. 

The formation of wound wood in the pith of Vitis was observed by 
Krieg, who ascribes it to the action of the products of decomposition of the 
woody part killed by the girdling. This wound wood consisted of parenchy- 
matous aggregations resembling pith spots. These were enclosed by a ring 
of cambium. The ring lying within the pith bark developed wood with 
numerous vessels tov/ard the inside and sieve tubes toward the outside. The' 
other pith spot, adjacent to the pith crown, formed the sieve tubes from its 
cambial ring toward the inside and wood toward the outside. The corre- 
sponding parts of both new structures united later with the respective parts 
of the overgrowth edge. In the meantime, the plant had replaced the wood 
already killed in girdling by the formation of new wood and sieve tissue 
in the pith. 

Page 825. We owe varied and careful experiments to Elsie Kupfer 
(Studies in Plant Regeneration. Dissertation of Columbia University, New 
York, 1907). Of these, we will emphasize first the experiments on root 
cuttings of Roripa Armoracia. Pieces of the root laid flat in the soil formed 
new shoots from the cambium of both the upper and under cut surfaces. If 
bark and cambium had been cut away, sprouts developed after a preliminary 
callus formation at different places near the vascular bundle and more 
abundantly at the upper than on the under end. The capacity to form 
sprouts, which otherwise is peculiar to the cambium, therefore, extends in 
this case to the callus tissue newly produced as a reaction to wound stimulus. 
Longitudinal sections of roots of Pastinaca sativa, which were laid hori- 
zontal in sand, developed new sprouts on both cut surfaces near the cam- 
bium. In isolated pieces of bark, sprouts were produced on the inner side 
and roots on the outer side. The isolated central cylinder formed only 
roots. 

The experiments with potatoes are very instructive. If any eye at all 
was left uninjured on some aerial shoot, this developed an aerial tuber. If 



88; . 

all the eyes were removed, only root formation took place. Pieces of 
potato tubers, from which the eyes had been cut out together with the 
adjoining tuber parenchyma, formed new eyes on these cut surfaces. In 
the potato leaves, either a simple formation of. roots appears at the under 
end of the petiole or a tuber swelling, containing starch, or a combination 
of the two, or a regular small tuber with eyes. 

As a total result of all the experiments for which blossom and fruit 
stems were also used wnth success, we may recognize that for regeneration 
the presence of an abundant reserve material is necessary. Pure white 
sprouts of different plants formed no roots. Darkening, or removal of the 
carbon dioxid, prevented regeneration. Since certain parts of the plant are 
not capable of regenerating one or another organ, even when all conditions 
are favorable, one is led to the point of view that different substances must 
be present which determine the formation of any certain organ. Such sub- 
stances should be thought of in the form of enzytnes, which are not present 
in all cells but are localized in definite parts of the plant body. 

Page 833. In regard to callus formation, which takes place between 
the bark shield and stock, Ohlmann expresses himself in his detailed work 
(Ueber die Art und das Zustandekommen der Verwachsung zweier 
Pfropfsymbiontcn. Centralbl. f. Bakteriol. usw. II, Vol. XXI 1908) as 
follows : "It seems, therefore, that callus formation may begin only at 
the bark shield. Sorauer states in regard to this question that no law for 
the tearing away of the bark may be determined. According to Schmitt- 
henner, the trunk splits in the youngest sapwood. I have investigated a 
great number of plants of widely different species in regard to this ques- 
tion. It was evident that the cambium remained intact on the bark. In 
more scattered cases, I noticed that a few cambial cells had remained 
hanging to the youngest wood. Nevertheless, I have noticed this so rarely 
that T cannot ascribe any significance to it." It should be remarked here 
that the author did the budding at a time "when the cambial activity was in 
full progress." In this case, the author was correct. If the budding is 
done later, however, then the cases obser\^ed by Sorauer become more 
numerous. 

Page 854. Blankinship describes a hleediiuj disease occurring fre- 
quently in Montana (North America) in Populus augustifolia, P. baP 
samifera, P. deltoides, etc. (Zeitschr. f. Pflanzenkh., Part i, 1908). The 
trees bled extremely from wounds and this was accompanied by the bleach- 
ing or yellowing of the foliage. At times the wounds on different axes 
developed into cavities filled with a gummy, half fluid mass. The exuding 
sap, laden with bacteria, had a sweetish taste and had often attracted large 
brown ants. 

A "Jaundice" of the poplar is connected with this bleeding disease, in 
which bleeding may also appear but more frequently does not. The foliage 
of the whole tree is bleached and dries up in the intercostal fields. Death 



follows after 3 to 5 years. The diseased trees stand generally in low places 
and the author is of the opinion that the increase of the alkali content in 
the ground water is to blame. This trouble is found in Montana not simply 
on poplars but also on other trees where irrigation is used. Drainage is 
advisable. 

Page 856. Minora Shiga (On the effect of a partial removal of roots 
and leaves upon the development of flowers. Journ. College of Science, 
Tokyo, 1907, Vol. XXIII, Art. 4), reports on the promotion of blossom 
development by the removal of the part of the roots. Different species of 
very different plants experimented on acted differently under the same 
manipulation. In Pharbitis, Pisum arvense and V^icia Faba the removal of 
the main root and small lateral roots cause an unusually early and luxuriant 
development of the blossoms. This was not the case in Fagopyrum. 
Cutting off of the side roots promoted the formation of blossoms in Vicia 
Faba and Pisum sativum var. arvense, but did not do so in Pisum Arvense. 

End of Vol. I. 



889 



INDEX TO VOLUME 1.* 



Of the numerous plant names cited in this volume, only those are included in the 
index of which detailed accounts have been given. To have named all the plants used 
as examples for certain cases of disease would have uselessly encumbered the index. 



Abcission of twigs 357-6o 

Abies 105 

Ablactation in grafting 831 

Acacia. Exudation of gum 707-8 

Acacia longifoUa, with intumescence. . .437 

— Microbotrya, with intumescence. . .437 

— pendula, with intumescence 443 

Acclimatization 40 

Acer 94 

Acer. Defoliation due to heat 411 

Acer campestre. Goitre gnarl 378 

— italum 160 

— Negundo. Discoloration 280 

— obtusatitni 160 

— palinatuni. Nanism 144 

— plantanoides. Discoloration 280 

— Psciidoplantaniis, var. Schwedleri. 

Discoloration 280 

Acetylene 744-47, 769 

Acetylene poisoning 746 

Acid content. Changes due to lack of 

light 668 

Acids in soil 240-41 

— of plant roots. Effect of neutrali- 
zation 402 

Acremonium 204 

Acremonium in sterile-head condition .. 5-14 

Acrocylindrium 204 

Acrospermum 54 

Aeration of the soil 241 

Aesculus . 154 

Aesciilits macrosfachya 105 

Agaricum 53 

Agaricus caiiipesfris 99 

Agathosma 134 

Ageratum 147 

Agrogyriim re fens, P. B 90 

Agrostenima Githago 74 

Ailanthus 102 

Air, Dilute. Effect 314 

— Aloist. Effect on plants injured by 

drought 425 

— Too dry. Effect 408-22 

Akrolein, Injury due to 757 

Albication 308 

Albinism 36, 677-^,4, 698, 847 

Alder bogs. Discoloration of water.... 251 

Alders. Death 153 

Algae, Green, as nitrogen collectors. .. .273 

Alinit 270 

Alkali grass 195 

— soils 267 

Alkalinity of the soil 367 



Allciitospora radicicola, Wakker 227 

AHittiii Cepa 30 

Alniis glntinosa 98 

— ■ — Fasciation 333 

Amanita rnuscaria 288 

Ammonia 720-2,2 

Ammonia, Free. Combination 272 

Ammonium salts. Use as top dressing. 268 

Use on meadows 363 

— sulfate 769 

Ainpelopsis hederacea. Emergences. .. .440 

Amygdalus Pcrsica. Nanism 144 

Amylocarbol 760 

Anabaena 1 1 

Anaesthetica 765-66 

Anastatica hierochuntica 176 

Andropogon nutans 696 

— ■ Schoenanthus (Jav. Sereh) 693 

— Sorghum. Mafuta disease 415 

Animals, Wild, Injury due to 781-83 

Annual-rings. Production 774 

Radial division 589- 

Annual-rings, False 615-17 

Anti-ferments 676 

Antibiosis 1 1 

Antinonnin 760 

Apcra spica venti 10 

Aphelandra. Intumescence 448 

.Aphids 392 

Apogamy 342 

Apostasis of the blossom 373 

Apostrophe 673 

Apple. Bitter pit 168-70 

— Canker 586-92 

— Tan disease 210-13. 

— Varieties for dry soils 175 

— Water-core 286-87 

— Wen formation 882 

— Woolly streaks in the cores. .. .324-26 

Apples, Winter. Storage 323 

Apricots. Mombacker disease 479 

Aprocrenic acid 240 

Araban 705 

Arabin 699, 705 

Arabinose 167 

Arachis hypogaea 690 

Araucaria 94 

Arrabbiaticcio 202 

Arsenic compounds. Injurious effects 

741, 752, 761 

Arundo arenaria, L 90, 150 

— baltica 150 

.Ascophora 54 



*It has seemed advisable to use the German index, adapting it where ever neces- 
sary for the translation, rather than to change the form entirely. (Translator's note). 



890 



Ascophora Beijerinckii 556 

Ashes. Showers 751 

Aspergillus . 13, 53 

Aspergillus niger 17, 99 

Starvation condition 288 

Asphalt fumes 732-35 

Asphalting o-f streets 106 

Aster alpiiuts 84 

Asteroiiia radiosiiin 734 

Atmospheric influences, Injurious.. .408-674 
Atmospheric moisture. See Humidity. 

Atoiiiaria linearis Stephn 221 

Aurigo 434-35. 460 

Autumn coloration 127, 500-4 

Autumn wood 774 

Avalanches 634 

Axial organs. Wounds 772-81 

Axillary proliferation 375 

Axis. Effect of constriction 817-21 

Azaleas. Leaf-fall 352 

AzoUa caroliniana 11 

Azotohacter 270, 273 

Azotohacter chroococcniii 270 

Azurine 765 

Bacillus albuminiis 273 

— antliracis 674 

— Berestnezvi 17 

— hetae 28 

— btityriciis 273 

— Cobb (Pseudonionas vascularum)..'or)-; 

— coli _. 273 

— coli communis 28 

— fluorescens liquefaciens 223 

— foetidus 273 

— liquefaciens 223, 273 

— liquidus 273 

— viasculicola 690 

— luegaterium 273 

— Mesentericus vulgatus 223. 273 

— mycoides 223, 273 

— nuhilis 273 

— phytophthorus 829 

— prodigiosus 273, 674 

— protCHS vulgaris 273 

— pseudo-arabinus 696 

— pyocyancus 674 

— radicicola 273 

— radicicola Beijerinckii 11 

— ruber balticus 17 

— sacchari 694, 696 

— subtilis 14, 223, 273 

— typliosus 674 

— ureae 273 

— vascularum 696 

— vulgaris 273 

— vulgatus 14 

Bacteriorhiza 11, 223, 271 

Bacterium coprophilum 273 

— fuscum 273 

— Hartlebi 272 

— nitrobacter , 273 

— pseudoarabinus 696 

— sacchari 696 

"Baking" of the soil 405 

Bamboo. Nanism 144 



Barium chlorid in waste water 752 

Bark. Casting 258 

— Injuries 797-810 

— Injuries from sunburn 647 

— Shedding 259, 328-31 

— Springing- 327-28 

- — Wounds due to hail 468 

Bark, Rotten 258-59 

Bark excrescences 329 

— grafts 831, 837 

• — scurvy 2)7- 

— tatters 575-76 

— tubers 861-71 

— warts 881 

Barrenness of hops 342-44 

Bassorin 699 

Batata. See Sweet potato. 

"Baumschutz" 760 

Bead cells 8 

Beans. Intumescences 446 

Beech, Red. Black blight 558 

Girdling disease 219 

Beets. Bacterial gummosis 697 

— Bacteriorhiza 223 

— Club root 871 

— Dry rot 415-16 

— • Fertilization with nitrate of soda.. 223 

— Frost action 531-32 

— Heart rot 415-16 

— Lightning effect 495 

— Over- fertilization 389 

— Running to seed, due to frost.. .516-18 

— Sterilization of seed 225 

— Tail rot 697 

— Unripeness .390 

— White-leaf condition 883 

— Working of the soil 226 

— See also Fodder beets ; Roots, 

Edible. 

Begonia fuchsioides. Leaf-fall 353 

Begonias, Tuberous. Dropping of the 

blossoms 417 

Bellis perennis 126 

Bending of branches 810-15 

Berberis 105 

Beta vulgaris. Rupture of roots 321 

Betula pubescens 249 

Biogen 32 

Biota 144 

Biota vieldensis 828 

— orientalis 105, 828 

Bitter pit in the apple 168-70 

Black-leg of the edible chestnut ....709-10 
Black-ring condition of horse-radish 717, 884 

Blackberry. Canker 606-7 

Blast 47 

Blasting of legumes 160-61 

Blastomania A. Br 378 

Bleeding disease of the poplar 887 

Blight 41, 608-13 

— Predisposition 52 

Blight, Black, of the red beech 558 

Blight caused by premature ripening. ... 156 

Blindness of the hop 342 

Blisters from sunburn 642 

Blorokziekte in coffee 230 



891 



Blossom development promoted b}' root 

removal 888 

— formation induced by starvation 

condition 289 

— organs. Changes due to frost. .518-23 
Blossoms. Apostasis 373 

— Doubling 375 

— Dropping 353 

— Faulty development. 416-19 

— Sunburn 645-46 

Blossoms, Sterile. Production 289-92 

Boletus 53 

Bordeaux mi.xture 761, 884 

Injury due to 884 

Preparation 885 

Boronia 134 

Borosma 134 

Bosses in ducts 570 

Bosuch of tobacco 685 

Botrytis 14, 27, 53 

Botrytis cinerea 14, 23, 394, 433, 706 

Bouillie Celeste 765 

Branch blight in forest trees 558-59 

— cuttings 821 -24 

— tips, Freezing back of older 553-55 

Branches. Bending 810-15 

— Internal splitting 581-83 

— Tvi^isting 815-16 

"Branderde" 243 

"Brausche" hops 344, 466 

Bread tree, St. John's. Swellings. . .339-40 

Breeding, Task of 665 

Brcniia Lactttcae 24 

Brenz-catechin 503 

Brindle of tobacco 685 

Brizopyrum 195 

Bromin 735-36 

Bromus mollis. Nanism 145 

Brousstn 863 

Brown-chains due to diptera larvae. .. .614 

Brusone disease of rice 315 

Bud cushions. Injury due to frost 577 

— cuttings in Vitis 828 

— disease 146 

— formation on leaves 378 

— variation 146-47 

Budding ._ 831, 833-38 

Buds. Injury from sunburn 645 

— Injury from too dry air 408-11 

— Pressure 378 

Buds, Accessory 561 

— Dormant. Death 862 

Bulbs, Blossoming. Failure in forcing 

297, 651-52 

"Bunt" of tobacco 685 

Burning of seed 186 

Burning out of grass 285 

Cabbage plants. Behavior in frost. .531-32 
Cacti. Cork disease 428-30 

— Classiness 453-57, 7^7 

— Internal intumescences 430, 454 

Caeoma 59 

Caeoiiia cerealium 59 

Caladiums. Tuber cuttings 828 

Calcipenuria 304 



Calcium. Excess 399-403 

Jaundice due to 310 

with grapes 402-3 

Calcium. Lack. Cause of silver leaf... 286 

— ■ — Changes due to 301-5 

— ■ — Cultural experiments 303 

Calcium arsenate, Injury from 761 

— • carbid 769 

— chlorid in waste water 751-52 

— chlorosis 881 

— fertilization with smoke poisoning. 772 

— nitrid 769 

— oxalate 792 

Contents of cells 792 

• Production by solution of car- 
bohydrates 792 

— sulfid 741 

Calda fredda 202 

Calico of tobacco 685 

Calluna 256 

Calhtna vulgaris 146, 242 

Callus 790 

— Girdling roll 787-97, 808 

Callus formation in graft symbionts. . .887 

— on stems of Malopc graiidiflora. . .443 

Calycanthus 105 

Cambium. Browning due to frost 612 

Cauielina saliva, sown to prevent lodg- 
ing 66s 

Camellias. Yellow foliage due to ex- 
cess of light 671 

Campanula 146 

Cancer 53 

Candying of seeds 226, 387, 389 

Canker 42, 47, 586-608 

Canker, Closed 587 

— Crotch, in fruit and forest trees. 593 -94 

— Open 587 

Canker from frost 583-85 

— in apple trees 586-92 

— in blackberries 606-7 

— ■ in cherry trees 594-96 

— in coffee 230 

— in grape vines 596-98, 6or 

— in roses 602-6 

— in Spirea 598-600 

— wounds 776 

Cannabis 147 

Cannonading against hail 470 

Caragona 105 

Carbohydrates, Production of calcium 

oxalate in solution of 792 

Carbolic acid 225, 760 

Carbolineum 757 

Carbon-dioxid. Effect 740, 746 

— Effect on germination 109 

— Excess 109, 406-7 

— Lack, Changes due to 316-19 

Carbon-disulfid 269 

Carcinoma 586-608 

Carex 256 

Carex arenaria L 150 

Caries Fabr 49, 56 

Carnations. Classiness 717 

Carotin 282 

Cassavas. Favorable soil 232 



892 



Cassia toincntosa. Intumescence 436 

Castanea 11 

Casting of the fruit spurs 338 

Catalase 676 

Cattleya. Specking 261 

Celery. Over-fertilization 392 

Cell membrane. Processes of loosening 
due to frost 581 

— passages 613 

Celosia cristata ;}^ 

Fasciation 334 

Centaur ea cyaiius 74 

Cephalosporium 240 

Cerasin 699 

Cerafoiiia Siliqua. Outgrowths on 

branches 339 

Ceratoptcris thalictroides 288 

Cereus flagelUformis. Cork disease. .. .428 

— nycticalus. Classiness 453 

Chagrinization of the rose stem 434 

Chaiiiaecyparis Lazvsouiana 159 

— sphaeroidia, var. Andalyciisis 828 

— sqnarrosa 828 

Changelings in grapes 346 

Check of plants 9 

Chemico-physical processes. Effect on 

soil absorption 264-68 

Chemotropism 13 

Cherries, Sweet. Sensitiveness 209 

Cherry. Canker 594-96 

— r)eath 154, 555 

— Effect of drought 281 

— Frost boils 572 

— Gummosis 699-707 

— Susceptibility induced by frost . 154, 555 

— Tan disease 213-17 

— Varieties for dry soils 175 

Cherry trees along the Rhine. Death 

due to frost 555-58 

Chestnut, Edible. Black-leg 709-10 

Root disease 219-20 

Chici on Gingko Bi'ioba 386 

Chile saltpeter 223, 311, 767 

Effect as top dressing 390 

Injurious effect 767 

Use with woody plants 391-92 

See also Nitrate of soda. 

Chilling, Disturbances due to 513-14 

Chimneys, Solid substances given off 

by y^y-^y 

Chloranthy 342 

Chlorin 724-29 

Chlorin. Lack, Changes due to 306-7 

Chlorophyllan 502 

Chlorosis 308, 881 

— Transmission by grafting 697 

Chlorosis due to calcium • 881 

— of grapes 402 

— of tobacco 685 

Chorisis 376 

Chorizema 134 

Circumvallation. Phloem 867 

— See also Overgrowth. 

Cladosporium 14^ 438, 545 

Cladosporium javanicum. Wakker 227 

— penicillioides 204 



Clasterosporiuin carpophiluin Lev. 

Aderh 706 

Clavus 50 

Clay soils. Cracking 189 

— — Disintegration 190 

Clefts due to frost 566-69 

Clefts due to Polyponts sulfiireus 568 

Climate, Continental 131-34 

— Marine 131-34. 

Climatic relations 134 

Cliz'ia iiobilis. Sunburn 643 

Clostridium gelatinosum 272, 2yi 

— Pastenriauum 270, 2y2 

Clover. Pleophylly 376 

Clover, Four-leaved 376 

Club-root of beets 871 

Coalescence. Natural processes S47-50 

Coating substances. Injuries due to.. 756-65 

Cobalt in waste water 755 

Cobb's disease of sugar cane 696-97 

Coccus caricac, Fab 710 

Cocoa. Fhytophthora decay 462 

— Unfavorable soil 231 

— Wind action 472 

Coffee. Black rust 230 

— Blorokziekte 230 

— Canker 230 

— Djamoer oepas 230 

— Root rot 231 

— Swarte roest 230 

— Unfavorable soil 230 

Coffee arabica 230 

— liberica 230 

Coffee plantations. Use of shade trees. 657 

Cold, Icturus from 309 

Colletotrichum 261 

CoUitris quadrivalvis 828 

Coloration, Autumnal 127, 500-4 

in trees 280-81 

— Red, due to excess of light 673 

— •— in grain ! 281-82 

Coloring matter, Red 127 

Colors, Warming up 127 

Commensalism 11 

Common salt. See Sodium chlorid. 
Compositae. Doubling of the blossoms. 375 

Cone disease of conifers 372 

Conifers. Blight of tops 487-89 

— Cone disease 372 

— Differences between lightning and 

frost wounds 489-93 

— Leaf blight from frost 883 

— Resinosis 711-16 

— Ring l)arking 615 

Conservatories, Sunburn in 643-44 

Consitution of soil. Unfavorable. 

Chemical 264-407 

Physical 138-263 

Constriction, Spiral twisting of wood 

fibers due to 817 

Constriction of the axis. Effect 817-21 

Contagium vivum fluidum of the mosiac 

disease 688 

Control plants. Cultivation 744 

Convallaria majalis 136 

Copper, Injuries due to 740, 761 



893 



Copper nitrate in waste water 754-55 

— rust of hops 283 

— solutions, Injuries due to 761 

5"^^ also Bordeaux mixture. 

— sprays. Intumescences after use 

on grapes 440, 762 

— sulfate in waste water 754-55 

Copulation 831, 838-39 

Cork disease of cacti 428-30 

— formation on fruits 432-34 

— holes 575-76 

— outgrowths 426-28 

— warts on grape stems 432 

Conius alba 105 

— }nascula 105 

— sanguinea 105 

— sibiiica 105 

Correa 134 

Corylus II, 105 

Coryneum Beijeriiickii, Oud 556, 706 

— cjunimiparum, Oud 708 

Cotton. Effect of fog 458 

— Stem browning 228 

— Unfavorable soils 229 

— Wilt disease 229 

Cow bushes ia6 

Cramp due to drought 281 

Crataegus 107. 127 

— Twisting 177 

Crenates 240 

Crenic acid 240 

Creoline 760 

Crippling phenomena, due to frost 508 

Crops, Preceding. Influence 275 

Crotch blight 594 

— canker in fruit and forest trees. 593-94 

Crust formation on soils no 

Cryptogams. Sexual organs 289 

- — Starvation condition 287-89 

— Tendency to dioecia 289 

Crystal-azurine Mylius 765 

Cucumbers. Splitting 462 

Cultivation. Methods. Injurious 

effect _ 756-71 

Cultivation of moor soil. Changes due 

to 256-58 

Cultures, Feeding, for soil 142 

Cupressus 144 

Cupressus Bregeoni 828 

— Lazi'soni 828 

— scuipervirens 828 

Currant. Black. Gnarl formation 382 

Cuticula. Rupture 623-24 

Cuttings. Production of new varieties. 827 

— Utilization of various organs. .825-29 

Cuttings. Leaf 873-78 

Cyathus 54 

Cycadeae n 

Cydouia zulgaris. Gnarl formation. .. .385 

Cynibidiiiiii Lowi. Intumescence 444 

Cystisus 105 

Cystospora Icucostoiua 706 

— rubesccns 556, 558 

Damping off of shoots 134 

Dasyscypha (Pezica) Willkommn 83 



Decay 196, 205 

Decomposition 196, 205 

Decomposition of proteins due to lack 

of light 669 

— of soil 196, 205 

Decorative plants. Drying of the in- 
florescences 296-97 

Excessive nitrogen fertiliza- 
tion 393-95 

Dedoublement 376 

Defoliation, Autumnal 527 

— Summer 347, 411, 661 

Defoliation due to frost 347, 527-31 

— due to growth 347 

— due to heat 347, 411, 644-45 

— due to turgor 351 

Deforestration. Bad effects 89 

Degeneration 34-40 

Dematophora nccatrix 710 

Dendrin 760 

Dendrobium. Specking 261 

Denitrification 269 

Dew, Capacity of sandy soil for becom- 
ing wet with 149 

Dew fall. Heavy 133 

Diaphysis 374 

Diaphysis of grain heads 466 

— of potatoes 163-64 

Dicotyledons. Resin formation 716-17 

Didymosphaeria populina 559 

Didymosporium salicinum 559 

Die-back of the orange 392 

Digitellus 53 

Dioecia. Tendency in crytogams 289 

— Tendency in ferns 289 

Dioscorea 232 

Diospyros Kaki. Nanism 144 

Diptera larvae, producing brown chains. 614 
Discoloration of Fagiis sik'atica 280 

— of trunks and branches 576-79 

— of woody plants 279-81 

Disease. Definition 9 

— Excitor . . . ; 27 

— Inheritance 31-34 

— Limitation of concept 5-7 

— Nature 5-40 

— Predisposition due to lack of 

light 666-70 

— Production 8-10 

— Special cases, due to elevation 

above sea-level 81-86 

Disease, Absolute 7 

— caused by smoke 49. 459 

— Felty 179 

— Relative 7 

— Shrivelling, of the mulberry .... 690-92 
Diseases, Constitutional 10 

— Enzymatic 675, 717 

— General 10 

— Leaf-casting 349-52 

— Local, of plants 10 

— Parasitic 13-19 

Diseases due to location of the soil. .72, 137 

— due to unfavorable soil condi- 

tions 72-408 

Djamoer oepas of coffee 230 



894 



Dongkellanziekte of sugar cane 228 

Dormancy 353 

Dormant eyes 785 

Dormant period 125 

Dothiora spliacroidcs Fr 559 

Double-rings 615-17 

Doubling 375, 376 

Dracaena. Yellow spots 435 

Drain mats 319 

Drain tile. Clogging 319 

Drainage 197, 232, 233, 267 

Draining of moor soil 257, 258 

Dropping of the flowering organs — 353-57 

— of the fruit 296 

— See also Casting; Shedding; Shell- 

ing. 

Dropsy 335-39 

Dropsy in grape cuttings 881 

— in pomes 338-39 

— in Ribcs aureiim 336 

— in small fruits 335-38 

— in stone fruits 338-39 

Drought 131 

— Effect on field products 155-57 

— Eflfcct on germination 157-58 

Drought, Jaundice due to 311 

— Physiological 245, 749 

Drought cramp 281 

— spots in grain 282 

— tears 568 

— with the cherry 281 

Dry-rot due to waste lime 195 

— of beets 415-16 

Drying of foliage, Premature 284-85 

Duct bosses 570 

Dunes 149 

Dwarf growth 76, 142-47 

— stock 105 

Dwarfing due to scarcity of water i-|5 

Ecblastesis 375 

Eel-worrns 855 

Electrical discharges 480-97 

Electricity, Efifects of experimental. 488, 882 

Electricity in city planting 493 

Electro-culture. Disadvantages 496-97 

Electrolytes 193 

Elm. Bark refuse 259 

Elymiis arenarius, L. . . 90, 150 

Embryonic plasma 31 

Emergences 434 

— in Ampclopsis liedcracea -!40 

Encrustation of the soil 134 

Endemics 19 

Endomyces vernatis Ludw 855 

Enzymatic diseases 675-717 

— functions. Displacement 675-717 

Enzymes 887 

Enzymes in plants 883 

Epidemics 19-23 

EpHobinm hirsntiim. Adaptation capa- 
city . ■ 2,22 

Epistropha:-;!'. . ... . . '. 673 

Eqiilsetiifh; pdtil'^f'e, -h., Formation of 

drain mats due to, 319 

'Ergot . . .... . . . •. ; 50 



Ericaceae. Root-ball dryness 181-82 

Erineum Pers 179 

Eriphorum 256 

Erysiphe Fabricii 49 

— graiiiinis 640 

Erysiphe Th 53 

Ether-forcing 765 

Etiolation .308, 654-57 

Etiology 7 

Eucalyptus. Intumescence 444 

Evaporation. Increase with lack of 

nutritive substances 318 

Evonymiis Japonica. Nanism 144 

Excrescences on hark 329 

Exoascus 146 

Experiments, Cultural, with lack of 

calcium 303 

Exposure, Southern 86 

Factors, Vegetative. Accumulation.... 38 

Fiiulc of tobacco 685 

Fagus II 

Fagus sih'atica. Discoloration ..280 

Fallow land 188-89, ^72 

Fames 53 

Familiola 53 

Fasciation 2,2,, 2,3y2,A 

— due to frost 559 

— in Picea excelsa 332 

Felty disease 179 

Fermentation, Alcoholic loo 

Ferments. Pectin 271 

Ferns. Apogamy 342 

— Tendency to dioecia 289 

Ferns, Viviparous 342 

Ferric sulfate. Sec Iron sulfate. 

Fertilization. Exhausting effect 266 

F"erti!ization, Salts for 192 

Fertilization of moor soil 257, 258 

— with green manure 234, 267, 271 

— with iron sulfate 402 

— with nitrate of soda 223 

— with potassium 129, 156 

Effect on growth 156 

— with sodium chlorid 193 

— with straw 269 

Fertilizers, Turning to peat 271 

— Injurious effects 767-71 

Fever reaction in plants 871 

Field Crops. Effect of drought 155-57 

Over-fertilization 392-93 

Fields. Spray lightning action 495-96 

Fig trees. Gummosis 710-11 

Filositas 161-63 

Flaccidity. Phenomena 8 

Flashes of lightning 480-87 

Flavor, Frosty, in grapes 518 

— Hard, in grapes, clue to hail 469 

Flax. Jaundice (le jaune) 283 

— Reds (le rouge) 283 

■ — Yellow (le jaune) 283 

Flocculency 193 

Flour. Loss of baking quality due to 

sprouted grain 321 

Flower clusters. Shedding in hya- 
cinths 365-67 



895 



Flower pots. Washing 205 

Flowering organs, Dropping 353 

Plowers, Green 342 

Flying ashes 738, 741 

Fodder beets. Root blight 220-26 

Fodder peas. Lodging 665 

Fog 458-60 

Fog. Effect on cotton 458 

— Protection against frost 511 

Foliage. Injuries 879-80 

— Perforation 427, 430-32, 444. 449 

— Premature drying 284-85 

— Yellowing due to frost 554 

— Yellowing in camellias due to ex- 

cess ■ of light 671 

Foliage, Older. Behavior with acute 

frost action 524-26 

Food concentration. Increase 360-87 

Food stuffs. Relation to the soil struc- 
ture 264-74 

Fool's-head formation in hops 342 

Forest litter 186-87, 270 

Forest trees. Crotch canker 593-94 

Isolation 327 

Forestration. Advisability 80 

Forests 134-37, 187-88 

— Use as protection . . . .- 1 50 

"Forks" of grapes 345-46 

Fox of the hop 282 

Freezing back of older branch tops.. 553-55 

— of heavy soil 235 

— to death 504-7 

Frenching disease of tobacco 685 

Friability, Dependence of tillage on 104 

Frost. Attack on immature growth ... .554 

— Behavior of beets 531-32 

— Behavior of cabbage plants. .. .531-32 
Frost, Acute. Effect on foliage 524-26 

— Black 537 

— Experimental production of par- 

enchyma wood by 617-20 

— Late. Damage 136, 432 

— Protection by fog against 511 

— Protective measures against. .. .624-30 

— Susceptibility o-f moor vegetation 

to ;25i-53 

— Theory of the mechanical action 

of 620-23 

— Varieties hardy to 500, 631 

Frost action. Effect on roots 562-66 

Special cases 514-637 

Theory as to nature 507-13 

— blisters 524, 53^-34, 569-74 

— boils of cherries 572 

— canker 583 

— causing cambial browning 612 

cell membrane loosening 581 

cell passages 613 

changes in blossom organs. .518-23 

crippling phenomena 508 

damage 136, 432 

deficient greening of younger 

foliage 526-27 

defoliation 347, 527-31 

differences in tension 514 

drying of cherry trees 555-58 



Frost causing dying of twigs 154 

• excessive chilling 508 

■ f asciation 559 

— — heaving of seeds 536-37 

injury to bud cushions 577 

injury to spring growth 559 

internal injuries to the grain 

stalk 539-41 

ir.ternal injuries to the young 

grain . . . . 537-41 

internal splitting of trunk and 

branches 581-83 

leaf blight of conifers 883 

medullary ray displacement. .. .571 

movement phenomena 547-53 

running to seed of beets. .. .516-18 

rust rings in fruit 523-24 

— • — splitting of leaves 534-36 

. stalk lodging 542 

super-cooling 508 

wihing 549-51 

yellowing of foliage 504, 554 

— clefts 566-69 

— curve 630 

— danger in sandy soil 149 

— holes 197 

— line ■ 579-81 

— plates 609 

— prediction 630-31 

— ridges 566 

— tears, Internal 569 

Open 583-85 

— wounds in conifers 489-93 

— wrinkles 574-75 

Frosting 504-7 

Fruchtkuchen 338, 339 

Fruit. Cork formation 432-34 

— Dropping 296 

— Hardy varieties 631-33 

— ■ Mealiness 166-68 

— Ripening, Premature 166 

— Rust rings due to frost 523-24 

— Rusting of the peel 170 

— Seedless 292-95 

— Self-sterility 291 

— Sprouting '. 375 

— Watery taste 323 

Fruit cushio-ns. See Fruchfkucheii. 

— spurs. Casting 338 

— trees. Crotch canker 593-94 

Root grafting 840 

— varieties. Advantages of pure 

planting 295 

for dry soils ^74-75 

Fruits. Double 376 

— Sunburn 645-46 

Fuligo vagaiis 56 

Fuiitago salicina. Tul 710 

Functioning. Maximum degree 9 

— Minimum degree 9 

— Optimum degree 9 

fungus mar'miis 53 

— ■ panis si III His 53 

Furrowing in heavy soil 234 

Furrows, Open 235, 511 

Fusarium 204 



896 



Fusariuin moschatuin 855 

Fusicladium 171 

Fusisporiuiii candiduin Lk 558 

Galactan 705 

Galactin 7^5 

Galactose 167 

Gallimaceus 5^ 

Gas, IlL.minating 744-47 

Gas phosphate 768 

Gas-works, Refuse 756 

Gases. Exchange 314 

Gases, Injurious. Effects 718-71 

Gayhead in tobacco 229 

Gelivure of the grape vine 495 

Gemmules 31 

Generation, Spontaneous 54 

Genista 150 

Geoponica 44 

Germ plasm 31 

Germination. Effect of carbon dioxid 

excess 109 

— Eft'ect of drought 157-58 

— Necessit}^ of oxygen 109 

— Tests 201 

Germination of seed in fruit 321 

in ice 499 

Germination power. Higher 125 

Retention 107 

Gingko Biloba. Chici 386 

Cylindrical gnarl 386 

Nipple 386 

Girdling 787-97. 885 

— Effect in grape culture 354. 788 

Girdling disease of the red beech 219 

Gladiola. Diseases 316 

Glassiness of cacti 453-57, 7^7 

— of carnations 717 

— of grain kernels 129-31 

— of orchids 651, 717 

Gloeosporium 261 , 263 

Gloensporium nervisequnin 304 

Gnaphalhitn Leontopodhim 84 

Gnarl, Cylindrical, of Gingko Biloba. . .3S6 
Gnarl formation on black currant 382 

on Cydonia vulgaris 385 

on Pirus Mains sinensis 381 

Gnarl tuber 863 

Goitre gnarl. Herbaceous 378 

on Acer cavipestre 378 

on Primus Padus 385 

on trees 378-87 

Gold of pleasure, sown to prevent lodg- 
ing 665 

Gouunose bacillaire 851 

Graft, Bark 831, 837 

— Cleft 831, 833. 838 

— Root 840 

— Saddle 831 

— Whip 837 

Graft symbionts. Callus formation. .. .887 

Grafting 829-47 

Grafting, Dwarf stock in T05 

— English tongue 845 

— Hybrid formation by 845 



Grafting. Mutual influence of scion and 

stock in 841-47 

— Transmission of chlorosis in 697 

— Yellowing of the stalk in 284 

Grafting by ablactation 831 

— by copulation 831, 838-39 

— by insertion 831 

— of grapes 844 

Grain. Blackening 72 

— Blasting 160-61, 282 

— Delayed ripening 365 

— Diaphysis 466 

— Drought spots 282 

— Effect of hail 464 

— Eft'ect of harvesting in the milk 

stage 295 

— Excessive straw growth 365 

— Glassy kernals 129-31 

— Internal injury due to frost. .. .537-41 

— Lodging 365, 662 

— Proliferated heads due to hail.... 466 

— Red coloration 281-82 

— Roots from seed tips 1 16-20 

— Spotted necrosis 372 

— Sprouting 320-21 

Grain, Winter. Harrowing 236 

Granulation of the rose stem 434 

Grapes. Bark warts 881 

— Canker 596-98, 601 

— Changelings 346 

— Chlorosis 402 

— Corky warts on stem 432 

— Double tips 345 

— Dropping of blossoms 354 

— Dropping of young berries 788 

— Effect of girdling 354. 788 

— Effect of spray lightning 493-95 

— Excess of calcium 402-3 

— Forked growth 345-46 

— "Forks" 345 

— Frosty flavor 518 

— Gelivure 495 

— Grafting 844 

— Hard flavor due to hail 469 

— Herbaceousness 345 

— Icterus 210, 402 

— Injury from sunburn 646-47 

— Intumescence 438 

after copper spraying 440 

— Jaundice 402 

due to excess of calcium 310 

— Leaf scorch 283 

— Maladie pectiquc 284 

— Parching 283 

— - Pectin disease 284 

— Red scorch 283 

— Scab 596-98 

— Shelling of the blossoms 354 

— See also. Vitis. 

Grapes, Seedless 355 

Grapholithia Cliernies 723 

— pactolana 7^3 

Grass. Burning out 285 

— Disappearance 362 

— Effect of excess of nitrogen 365 

— Influence 276 



897 



Grasses. Red coloration 282 

Gray sand 243 

Green-manure fertilization ....234, 267, 271 
Greening of inflorescences 341 

— of younger foliage. Deficient. .526-27 
Ground water level. Depth in moor soils. 257 

Lowering 106, 150-52 

Raising 183 

Growth. Arrestment due to radium rays. 672 
due to Roentgen rays 672 

— Defoliation 347 

— Effect of humidity 423-25 

of potassium fertilization 156 

Growth, Double 156 

— Immature. Effect of frost 554 

— Twisted '. 774, 821 

Giiignardia Bidivellii 26, 669 

Gum cells 851 

Gum exudation in Acacias 707-8 

in bitter oranges 708-9 

in plants 707-17 

Gummosis. Use of vinegar made from 
wine 707 

Gummosis of cherries 699-707 

— of fig trees 710-11 

— of olives 711 

Gymnosporangium 53 

Gymuosporanghim Sabinae 62 

Gunnera 11 

Gypsum 195, 250, 402 

Habitat. Effect of changes on herba- 
ceous plants 72-75 

Habits, determining peculiarities in 
plants 39 

Hail 463-70 

— Effect on grain 464 

— Effect on hops 466 

— Effect on potatoes 466 

— Effect on rape 466 

— Effect on tomatoes 467 

Hail, cannonading against 470 

— • causing bark wounds 468 

hard flavor in grapes 469 

lodging of the stalks of grain.. 542 

— — proliferated grain heads 466 

Handles on trees 848 

Hard-shells of seeds 115, 420 

Harp-trees 93 

Harrowing 236 

Harvest. Decrease due to tree shade... 657 

Health. Latitude 9 

Heart rot 615, 851 

due to waste lime 19; 

of beets 415-16 

of horse radish 717 

Heart wood. False 851. 852 

Wound 852 

Heat. Death 638 

— Defoliation 347, 411-12, 644-45 

— Excess 638-53 

Premature ripening 640 

See also Sunburn. 

— Lack 498-637 

Heat rigor 638 

Heath soils. Disadvantages 242 



Helianthns annus. Effect of defoliation. 341 

Helichrysum I34 

Helotium 54 

Hemi-celluloses 705 

Hemi-parasites i- 

Hemi-saprophytes 12 

Herbaceousness in grapes 345 

Hericia §55 

Hibiscus vitif alius. Intumescence 448 

Hieraciuin alpinum 84 

Hilling of heavy soil 234 

Hippeastrum 127 

Hippophac rhamnoides. L 90, 150 

Hoar frost 636 

Summer 637 

Hoeing of the soil 184. 234 

Holoparasites 12 

Holosaprophytes 12 

Homogamv 293 

Honey dew 55. 412-15 

Hops. Barrenness 34^-44 

— Blindness 34^ 

— Copper rust 283 

— Effect of hail 466 

— Eft'ect of shading 283 

— Fool's head formation 34^ 

— Fox 282 

— Heating 344 

— Pole red 283 

— Red tan 282 

— Reds 282-83 

— Summer rust 282 

Hormodendrum disease 742 

Horn prosenchyma 707 

Horn shavings. Use as fertilizer. . .393, 395 
Horse radish. Black ring condition. 717, 884 

Heart rot 7U, 884 

Horticulture. Use of sand 261 

— Use of sphagnum peat 260 

Hot bed plants. Wilting 277 

House plants 419-20 

Leaf fall 352 

Humea I34 

Humic acid 241, 722 

Humidity 123 

— Effect on mode of growth 423-25 

Humidity, Excessive. Effect. .75, 123, 423-57 

Humin 241 

Humus, Raw I49, IQO. 242. 271 

Humus fermenting organisms 272 

— • sandstone 243 

— substances I5i 

Hyacinths. Ring disease of bulbs. 326-27, 451 

'^ Shedding of the young flower 

clusters 356-57 

— Skin diseases 451-53 

Hybrid formation by grafting 845 

Hydrochloric acid 724-29 

Hvdrocvanic acid 761 

Hydrofluoric acid 729-30 

Hypochlorin S02 

Hypocrea rufa I7 

— Sacchavi 227 

Hypoplasia 1/7 

Hypoxylon 53 

Hvsterium 54 



898 



Ice, Germination of seed in 499 

Ice coating 634-37 

— formation. Favorable effect 510 

Icicles 634-37 

Icterus 307-12 

— due to cold 309 

— of grapes 310, 402 

Idioplasm 31 

Igniarius 53 

Immunity 128 

Imniunit}^ and predisposition 27-31 

Imrnunization, Artificial 23-25 

Inertia 39 

Inflorescences. Proliferation 374 

— See also Blossoms ; Flowering 
organs. 

Inflorescences of decorative plants. Dry- 

ng 296-97 

Ii-heritance. Nature ^2 

Inheritance of disease 31-34 

Inscriptions, Wounds due to 781 

Intra-molecular respiration 99, 313 

'-ntumescence. Internal 447 

"ntumescence after copper spraying. .. .762 
' — due to spraying injury 441 

— on Acacia longifoUa 437 

— on Acacia niicrobotrya 437 

— on Acacia pendula 443 

— on Aphelandra 448 

— on beans 446 

' — on cacti. Internal 430, 454 

-^ on Cassia t anient osa 436 

— on Cymbidinni Lozvi 444 

— on Eucalyptus 444 

— on grapes 438 

— on Hibiscus ritif alius 448 

— on Mynnccodia echinata 437 

— on peas 446 

— on Pelargonium ::ona!e 438 

— on Ruellia 448 

Intumescences 432, 435-49 

Intumescentia 435 

Inundations 195-96 

Iron. Lack 307-12 

— Occurrence in waste water 753-54 

Iron silicates 251 

— sulfate 881 

— • — Fertilization 402 

— sulfid 2=^0 

Iron-spottedness of potatoes 391, 882 

Irrigation of soil 182-83, 196 

Ishikubyo of the mulberry 690 

Isolation of forest trees 327 

Isopynini biiennituni 12 

Jadoo fibre 263 

Jahresbericht, Botanischer 60 

Jaundice 307-12 

— caused by drought 311 

lack of iron 307-12 

lack of nitrogen 310 

lack of potassium 310 

Jaundice (le jaune) of flax 283 

— of grapes 402 

due to excess of calcium. . . .310 

— of poplars 887 



Lc jaune of flax 283 

Juglans 107 

Juniperus. Rooting of branches 254 

Jnniperus communis 105 

— phoenicea. Bending by wind 475 

— Sabiua 105 

Juvenile form, Retrogession to the 277 

Kainit 404 

"Knick" 192 

Krados 42 

Lactic acid. Injury from factories pro- 
ducing 761 

Laelia. Specking 261 

Land. Conversion into swamps 196-99 

Land plaster. See Gypsum ; Plaster, 
Land. 

Landslides. Effect 90 

Larch. Retrogression in its cultivation. 81-84 

Latitude. Greater dift'erences 120-31 

Latitude of health 9 

Latitude of life 9 

Laurus 133 

Layering. Quinces 816 

Leaching. Soil 243 

Lead. Injuries due to 740 

Lead nanism 753 

— sand 243 

Leaf. Aurigo 434 

Leaf blight of conifers 883 

— casting diseases 349-52 

• — cur! of potatoes 395-99. 882 

— cuttings 378, 873-78 

— edges, dried by hydrochloric acid.. 724 

— emergences 434 

— fall in azaleas ' 352 

in Begonia fuchsioides 353 

in house plants 352-53 

in Libonia floribunda 353 

See also Defoliation. 

— injuries 871-73 

— mould. Use with orchids 262 

— perforation 427, 430-32 

— scorch of vines 283 

— spot diseases of sugar cane 228 

— wilting 365 

Leaves. Bud formation 378 

— Cork outgrowths 427 

— Falling 346-49 

— Injury from wind 477 

• — Splitting from frost 534-36 

— Sunburn in nature 641-43 

— See also Foliage. 

Leaves, Bitten 430-32 

— Perforated 430-32 

Legumes, Blasting 160-61 

Leguminosae, Advantages to soil of 

growing 232 

Leguminosae seeds. Flard shells. .. .420-22 

Light lines 420 

Lenticels 215 

— in potatoes 369 

Lepidium sativum 74 

Leptosphaeria. Lodging of grain stalks 

due to 542 



899 



LeptotliyriiDii poiiii Mntg 170 

Leuconostoc Lagerheiniii Ludw 855 

Libert ella fagiiica. Desm 558 

Libonia floribuiida. Leaf fall 353 

Lichenism 11 

Lichens on trunks 331 

Life. Latitude 9 

Light. Excess 671-74 

Red coloration 673 

Shadow pictures 673 

• Yellow foliage in camellias 671 

— Lack 654-70 

Changes in acid content in 

plants 668 

Protein decomposition 669 

Sugar blocking 667 

Lightning. Effect on beets 495 

— Effect on potatoes 495 

— Flashes 480-87 

— Internal striking 486 

Lightning, Spray 486 

Effect on fields and meadows 

• 495-96 

Effect on grape vines 493-95 

Lightning wounds in conifers 489-93 

Lignification of roots 179-80 

Ligustrnm T05 

Liliaceae. Faulty blossom development. 417 

Lily-of-the-valley. Failure 395 

Lime. Scarcity indicated by sorrel 237 

Lime kilns. Tar vapor y^j 

Liming 194, 238 

— Periodic 268 

Lingua 53 

Liiium iisifafissiiiiiiiii 107 

Liquids, Injurious. Effect 718-71 

Lithiasis 170-74 

Litter. Cautious removal 149 

— Excessive use 194 

— Layers 242 

— Raking 190 

Loam, Loose 191 

Lodging 131 

— of fodder peas 665 

— of grain 365, 662-66 

— of grain stalks 542 

Longevity due to grafting 839-40 

Lopas ..43 

Loranthus 56 

Lorantluis scnegalciisis 708 

Loupe S63 

Loxas 43 

Lutidine 460 

Lychnis diiinia 147 

— vcspcrtina 147 

Lyciuiii barbaruiii, L 150 

Lycogala 53 

Lycopus citropaciis. Adaptation 322 

Lysol 760 

Lythrum. Adaptation ^22 

Mafuta disease of Andropogon sor- 
ghum 415 

Magic ring, Pomological 789 

Magnesium. Excess 399-402 

— Lack. Changes due to 305-6 



Magnesium chlorid in waste water 

• ••••. 750, 751-52 

Magnesium compounds, Concentrated. 

Poisonous effect 361 

Magnolia hypolettca 159 

Maise. Unfavorable soil 231 

.1/0/ de mosaic of tobacco 685 

Mai della bolla of tobacco 685 

Mai della gamma 708 

Mai ncro 219-20, 709 

Maladie pectique of grapes 284 

Malformations 57, 73 

Malope grandiflora. Stem calluses 443 

Mains sinensis. See Pirns mains sinensis. 

Maminia fimbriata 559 

Manna. Exudation T'li 

Mannan ^05 

Manniok 2:32 

Manure, Green 234, 267, 2>i 

— Stable. Fresh 269 

Marciume del Pica 710 

Markasit 25b 

Market varieties 13? 

Marling 194, 238 

Marling, Scurvy from 370 

Marshy change in soil causing frost 

susceptibility 106 

Manche of tobacco 685 

Meadow ore 192, 243-49, 251 

Meadows. Effect of excess of potas- 
sium 40f^ 

of harrowing >:36 

— Improvement 362 

Meadows, Changes in 362-64 

— Moor 260 

— Mossy 364 

— Rankly growing places in 364 

— Spray lightning on 495-96 

— Use of ammonium salts on 363 

Mealiness of fruit 166-68 

Measures, Protective, against frost. .624-30 

Mechanics, Developmental 66 

Medullary rays. IDisplacement due to 

• splitting 571 

Excrescences 380 

Mclaeris 412 

Melligo 412 

Mcrcurialis annua 147 

Metamorphosis, Progressive 2)72-77 

— Retrogressive 340-44 

Methods, Preventative 23 

Micrococcus dendroportlios.. Ludw 855 

Mildew 42 

— See also Rubigo 

Milk stage, Effect of harvesting grain 

in 295 

Millet. Brush. Unfavorable soil 232 

— Xegro. Unfavorable soil 232 

— • Sorghum. Mafuta disease 415 

Mimosa pudica. Drought cramp 281 

Mimulus Tilingii 76 

Minimum, Law of the 299 

Mites 855 

IMobilization of reserve substances 106 

Moisture 319 

- — Fluctuations 273 



900 



Moisture. Lack 275-87 

causing changes in produc- 
tion 278-79 

tip blight 189 

in the soil 182 

Moisture, Atmospheric. Sec Humidity. 

Mombacker disease of apricots 479 

Mongrel disease of tobacco 685 

Moiiilia ciiierea 706 

— fructigena 706 

IMonstra : 57 

Monstrosities S7 

Moon-rings 613 

Moor plants, Horticultural 260 

Moor soil. Bacterial flora 256 

Changes through cultivation. 256-58 

Depth of ground water level... 257 

• Disadvantages 240-63 

Draining 257 

Fertilization 257-58 

Potassium chlorid treatment. . .257 

Sanding 256 

Moor vegetation. Susceptibility to 

frost 251-53 

Morphaesthesia 139 

Mosaic disease 229, 684-89 

Contagium vivum fluidum 688 

Effect of cultivation 687 

Predisposition 687 

Virus 687 

Mosaikhetegsege of tobacco 685 

La Mflsaique of tobacco 685 

Movement phenomena, due to frost. .547-53 

Mucor 53, 766 

Mucor albus 53 

— racemosus toi 

— spinosus 99 

— stolonifer 13, 10 1 

IMulberry. Ishikubyo 690 

— Shikuyobyo 690 

— Shrivelling disease 690-92 

Mulching 184-85. 235 

Mules disease of potatoes 161-63 

Multicolor of potatoes .*. .391 

Mycoplasm 34 

Mycorrhiza 11 

Myrmecodia echinafa. Intumescence. . .437 
Myrtus 133 

Nanism 142-47 

Necrobiosis 703 

Necrosis 56 

— Spotted 372. 741 

Nectria ditissitiia 46. 137, 588, 592 

Neptun 760 

Nickel in waste water 755 

Nicotine 460 

Niellc of tobacco 685 

Nidularia 53 

Nipple on Gingko Biloba 386 

Nitrate of soda fertilization 193, 223 

See also Chile saltpeter. 

Nitric acid 730 

Nitrogen 270 

— Excess. Effect 365, 387-99, 709 

Effect on rhubarb 392 

Retarding effect on ripening. . .394 



Nitrogen. Lack. Changes in produc- 
tion 287-98 

Nitrogen fertilization. Excessive. Effect 

on decorative plants 393-95 

— hunger 270 

Jaundice 310 

— storage by bacteria 270 

Nutriment. Increased concentration. 360-87 

— Lack_ 175, 275, 2S7-319 

— Relation to plants 274-319 

Nyctomyces 56 

Nyctoinyces caiididiis 614 

— uUlis 614 

Oculatio'U. See Budding. 

Oecological variations 73 

Oedema 335-39 

Oil fumes. Injury 757 

Olive. Gummosis 711 

Olivile 711 

Ooze coating. Injury to sewage dis- 
posal beds 366 

Ophiobolus 137 

— causing lodging of grain stalks. .. .542 

Optimum degree of functioning 9 

Opuntia. Cork disease 429 

Orange. Die-back 392 

Orange, Bitter. Gummy exudation. . .708-9 
Orchids. Classiness 651, 717 

— Specking 261-63 

— Use of leaf mould 262 

Organism. Cultural aim 6 

— Developmental mechanics 66 

— Force of self-preservation 6 

— Self -purpose 6 

Organs, Axial. Wounds 772-880 

Organs, Sexual, in cryptogams 289 

Orobus vermis 75 

"Orterde" 243 

Osiuunda regalis 288 

Outgrowths on roots 191 

Over-fertilization of celery 392 

— of field plants 392-93 

— of rhubarb 392 

— of vegetables 392-93 

Overgrowth edges, Gnarly 859-61 

Overgrowth of wounds 776-81, 783 

Oxalate of calcium 792 

Oxalic acid 22^, 449 

content of edible roots 223 

Oxalis crenata 109 

O.xygen. Excess. Effect 315 

— Lack. Effect 313-16 

Suffocation 313 

— Necessity in germination 109 

Oxygen rigor ^IZ 

Oxyphen acid 503 

Pacoiiia arborea. Bud cuttings 828 

Pan-genesis 3^ 

Panachure. See Variegation. 

Pandaiius javanicus. Yellow spots 434 

Papaver souuiifcrtttii. Pistillody 372 

Parasites. Energy of growth 15 

— Nutritive substrata 17 

Parasites, Facultative 15 

— Obligate I5 



901 



Parasites. Wound iS 

Parasites of weakness 15 

Parasitism 12 

Parching of grape vines 283 

Parenchyma wood. _ Experimental pro- 
duction by frost action 617-20 

Parenchyma wood aggregations 613-15 

Parenchymatosis 5, 338 

Parthenogenesis 178, 342 

Pathogeny 7 

Pathography 7 

Peach buds. Dropping 645 

— rosette 698 

— rot 763 

— yellows 697-99 

Peanut diseases 690 

Pears. Lithiasis 170-74 

— Stoniness 1/0-74 

— Varieties for dry soils... 175 

Peas. Intumescence 446 

Peas, Fodder. Lodging 665 

Peat, Sphagnum, in horticulture 261 

Peat mulch 265 

Peatrification of the fertilizer 271 

Peaty earth 185 

Pectiiie 167 

— disease of grapes 284 

— fermenting organisms 272 

— ferments 27 1 

Peeling of bark by game 781 

Pcli-sein of tobacco 685 

Pelargonium. Bud disease 146 

Pelargonium conalc 438 

Penicillium 14, ^2}, 766 

Penicillium glauciiiii 13, 204, 451 

Pcnnisctiim spicaliini. Unfavorable 

soil 232 

Pentoses 167 

Perforation of the foliage 

•-.•••.•. ; • • -4^7, 430-32, 444, 449 

Periodicity, Corrective 38 

Pcrouospora viciac 446 

Pestilences, Chart of 23 

Petalody 372 

Peziza 53 

Pes'iza JVillkoiniiiii 83 

Phalaenopsis amabilis, var. Riiiicnstadi- 

ana. Specking , 261 

Phaseolus 30, 126 

— Effect of lack of calcium 304 

Phenol 460 

Phenomena, Life, at low tempera- 
tures 498-500 

Phenyle, Little's Soluble 760 

Phillyrea. Wind-bending 475 

Philodendron. Grafting experiments. . .838 

Phleom. Circumvallation 867 

Plilcu})i pratcnse. L 125 

Phoma II, 261 

Plwma Betac, Frank 222 

Phosphoric acid. Excess 405-6 

Lack 300, 312 

Phosphorus. Lack. Effect 312 

Phragmidium 59 

Phyllachora pomigena (Schw.) 170 

Phyllerium Fr 179 



Phyllocactus. Cork disease 429 

Phyllody 340-44 

Phyllomorphosis 341 

Phyllosticta 261 

Phyllosticta Sycopliila. Thiim 710 

Phytopathology 7 

— Historical survey ._ 41-71 

— Periodical literature '. 66 

Ph\ tophthora 62 

Phytophthora decay of cocoa fruits. .. .462 

Phytophtlwra infcstaiis 21 

Phytoptus 146 

Picea 105 

Picea cxccha. Fasciation t,t,2 

Picoline 460 

Pigment, Red 127 

Pilobolus 54 

Pilosis 177-79 

Pimelea 134 

Pine. Dropping of the needles 349 

— Shedding of the bark 259 

— See also Pinus. 

Pineapple. Failure 650 

Pinosol 760 

Pinus 105 

— Nanism 144 

Pinus niontana 247, 475 

— siJvcstris 94, 107 

f. turfosa 249 

— See also Pine. 

Piricularia Oryzea Br. et Cav 315 

Pirns conununis 281 

— Mlalus sinensis. Gnarl formation . .381 
Pissodes H erciniae 723 

— scahricoUis 722, 

Pistillody . 372 

— in Papavcr somuifcruni 372 

Pisum II 

Pisnvi sativum 107 

Pith bridges 577 

— ■ repetition 613 

— spots 613 

Plant coverings. Effect ■ 275-76 

Effect on soils 185-86 

— diseases. Classification 48 

• — diseases. Constitutional 10 

— • — ■ General 10 

Local TO 

— hygiene 71 

— protection 59 

Plantago alpina 84 

— maritima 84 

Planting. Depth 103 

Planting, Autumnal. Precautions 565 

— Too deep 98-120 

— Too shallow 105 

Plants. Burning in moist soil 199-200 

— Check 9 

— Cultural position 55 

— Dormant period 125 

— Etiolation 423 

— Law of inertia 39 

— Peculiarities determined by habit.. 39 

— Power of resistance 18 

— PrO'tective devices against para- 

sites 18 



902 



Plants. Relation to environment 10-13 

— Relation to nutritive sub- 

stances 274-319 

— Rupture of fleshy parts 321-34 

— Statistics of disease 71 

— Stunting 1/5-77 

Plants, Herbacious. Efifect of changes 

in habitat 72-75 

— Tropical 190 

— Woodv. Adjustment of root 

body 78-81 

Development of axis 76-78 

Plants injured by drought. Effect of 
moist air 425-26 

Plasm, Embryonic 31 

— Hereditary 31 

Plasiiiodiopliora Brassicac 364 

Plasmopara viticola 280 

Plaster, Land 195, 237-40, 250, 402 

Plaster fertilization 237-40 

Plastiden theory 62 

Plastidules 31 

Platanus Grieiitalis. Effect of lack of 

calcium 304 

Plectridia. Pectin fermenting organ- 
isms 272 

Pleophylly 376 

Pleospora guiiiniipara. Oud 708 

Plowing, as inducing soil ripening 273 

Plowing, Deep, in heavy soil 234 

Plums. Tan disease 218 

— Varieties for dry soils 175 

Plums, Rusty 166 

Poa alpina 76 

Podocarpus. Nanism 144 

Podosphaera leucotricha. Salm 640 

Poefih of tobacco 685 

Poisoning due to lack of calcium 304 

— of soil 266 

Pole red of hops 283 

Polycladia 146 

Polygonum aniphibiiini 176 

— viviparuiii 76 

Polyporus sulfureus 568 

Polysarchia 53 

Pomes. Dropsy 338-39 

Pomological magic ring 789 

Poplar. Bleeding disease 887 

— Jaundice 887 

Poplar, Pyramidal. Death 558 

Position, Cultural, of plants 55 

— Horizontal. Efifect of changes. .. 120-28 

Pot cultures. Soil 140 

Potassium. Excess 403-5 

— Lack. Efifect on production. . .298-301 
in Ster'igmatocystis nigra 300 

Potassium chlorid treatment of moor 

soil _ 257 

Potassium fertilization 129, 156 

Potassium hyperchlorate 767 

Potatoes. Aerial tubers 165 

— Bacterial ring disease 398 

— Black dry rot 391 

— Brown specks on foliage 397 

— Cultural varieties 209 

— Diaphysis 163-64 



Potatoes. Efifect of hail 466 

— Enlarging of the parent tuber 398 

— Iron spottedness 391, 882 

— Leaf curl 395-99, 882 

— • Lenticels 369 

— Lightning efifect 495 

— Mules 161-63 

— Multi-colored condition 391 

— Over-fertilization 390-91 

— Perforation of the foliage 430 

— Premature ripening 161 

— Prolepsis 163 

■ — Running out 208-209 

— Rupturing of the stem 321 

— Scurvy, Deep 430 

— Secondary tuber formation 163 

— Thread formation 161-63 

— Tuber cuttings 828 

formation without foliage 164 

— Turning sweet 514-16 

— Water ends 163 

Potatoes, Seed. Method of cutting 828 

Pots, Flower. Washing 205 

Potted plants. Encrustation of the soil. 205 

Souring 203-206 

Use of saucers 208 

Pox of tobacco .689-90 

Prateolus 53 

Predisposition 25-26, 27-34, 52, 62, 

S3, 128, 223, 225, 301, 666-70. 
Predisposition. Abnormal 26 

— Hereditary 83 

— Normal 26 

Predisposition and immunity 27-31 

— to blight 52 

— to disease, Inheritance 31-34 

— due to lack of light 666-70 

— due to lack of nutriment. . . .301 

— in beets 223, 225 

in edible roots 223, 225 

— to the mosaic disease 687 

— to the smoke diseases ~22 

— See also Disposition. 

Pressure of the buds 378 

Production. Changes due to lack of 

nitrogen 287-98 

Prolepsis of the potato 163 

Proliferation 374 

— Axillary 375 

Proliferation of the inflorescences 374 

Prophylaxis 7 

Prosenchyma, Horn 707 

Protandry 293 

Proteins. Decomposition due to lack 

of light 669 

Prothallia, Ameristic 288 

Protog\'ny 293 

Prunulus 53 

Prunus 107 

— Nanism 144 

Prunus avium. Discoloration 280 

— Cerasus. Discoloration 281 

— domestica. Discoloration 280 

— Padus. Goitre gnarl 385 

— persica. Discoloration 280 



903 



Psettdoiiioiias (Bacillus Cobb) z'ascu- 

laruni 697 

— cainpestris 223 

Pscu(iope:;ica traclieiphila 284 

Psychro-clinic blossoms 548 

Puccinia 53, ^37 

Puccinia dispersa 128 

— glumarmn 128 

— graminis 66, 128 

Pulteneae I34 

Pure-planting of fruit varieties. Ad- 
vantages 295 

Pyridine 460 

Pyrites 250 

Pyrus cydoiiia 51 

Pythium 22y 

Pythhtm de Baryanitni 222 

Ottaternaria Perscooiiii Tul 558 

Onercus pednnculata 80, 9S 

Quinces. Layering 816 

Races, Biological 15, 128 

Radium rays, Arrestment due to 672 

Rain storms 461-62 

Rape. Effect of hail 466 

Raw-humus 241-43 

Red-rot 615 

Red-scorch of grapes 283 

Red-tan of hops 282 

Reds (le rouge) of flax 283 

— of hops 282-83 

Reductases 676 

Regeneration 887 

Relations, Climatic 134 

Reseda odorata 126 

Reserve substances. Mobilization 106 

Resin boils 712 

— formation in Dicotyledons 716-17 

— • galls on stilt roots 96 

— gathering causing wounds 780 

Resinosis, Acute 716 

— Chronic 716 

Resinosis of conifers 711-16 

Resistance. Plant power 18 

Respiration, Intra-molecular 99, 313 

Refiiiospora ericoidcs Zucc 828 

Retrogression to juvenile form 377 

Rhabditis 855 

Rhamnus 105 

Rhaninus Frangula 98 

— ptimila 76 

Rhhobitivi Beijerinckii 270 

— Leguminosarum. Frank ir 

— radtcicola 270 

Rhodanammonium 769 

Rhubarb. Acid retrogression with 

nitrogen excess 393 

— Over-fertilization 392 

Ribes 105 

Ribes aurenm. Dropsy 336 

— nigrum. Gnarl formation 382 

Rice. Brusone disease 315-16 

Ricinus 100, 229 

Ricinus coiiinninis 126 

Ring barking in conifers 615 



Ring disease of hyacinth bulbs. .326-27, 451 

Ringing. See Girdling. 

Ripening. Retardation due to excess of 
nitrogen 394 

Ripening, Premature 166 

cause of blight 156 

caused by excess of heat 640 

of fruit 165-66 

— — of potatoes 161 

Ripening of grain, Delayed 365 

Robinia 154 

Robinia Pseudacacia 107 

Roentgen rays. Arrestment due to 672 

Roesleria hypogaea 710 

Rolling .184 

Roncet 851 

Root acids. Effect of neutralization. .. .402 

— adjustment of woody plants 78-81 

— curvature 138-42 

— cuttings 828, 886 

— decay 196 

— decay due to marshy soil 196 

— disease of the true chestnut. .. .219-20 

— grafts .^ 840 

— growth 870 

— injuries 856-59 

— plants, Wilting of the foliage 365 

— removal, promoting blossom de- 

velopment 888 

— rot. Coffee 231 

Sugar cane 227-28 

— tubercles 80 

Root-ball dryness of the Ericaceae. . 181-82 
Roots. Freezing 562-66 

— Lignification 179-80 

— ■ Outgrowths 191 

— Scurvy, Deep 367 

Girdle 368 

Knotted 367 

Surface 367 

— Secretion 139, 151, 270 

Roots, Edible. Black-leg 220-26 

Blight 220-26 

Oxalic acid content 223 

Predisposition to disease. . .223, 225 

The threads 220-26 

See also Beets. 

Roration 44 

Ros mellis 412 

Rosa 107 

Rosa chinensls. Jaqu. Green blossoms. . .342 

— gallica 105 

Rose. Canker 602-6 

— Chagrination of the stems 434 

— Granulation of the stems 434 

"Rose-kings" 373 

Rosette growth 146 

— shoots 377 

Rost of tobacco 685 

Rot. Black, drv, of potatoes 391 

— Red ....' 615 

— Wet 22 

Le rouge of flax 283 

Rouille blanche of tobacco 685 

Rubber plant. Tubercle disease 449-Si 

Rubigo 44, 49, 53 



904 



Rubigo. See also Mildew. 

Ruellia. Intumescence 448 

Riiinex acetosella I47 

Indication of a scarcity of lime. 237 

Running out of potatoes 208-20L) 

Rupture of flesh}- parts of plants 3-I--4 

Rust 44 

Rust, Black, of coffee 230 

— White, of tobacco 690 

Rust of the plum 166 

Rust rings in fruit due to frost 523-24 

Rusting of the peel of fruit 170 

Rusts of sugar cane 696 

Sabre growth ... 474 

Saccharogcnsis diabetica 55 

Saccharoinyces Ludzuigii, Hans 855 

Saccharomycetes 100 

Saddle grafts 831 

St. Elmo's fire 488 

St. John's bread tree. Swellings 339-40 

Salix arenaria. L 150 

— cincrea 98 

— hci-hacea 84 

— reticulata 84 

— serpyllifolia 76 

Saltpeter. See Nitrate of soda; Chile 

saltpeter. 

Salz'inia nataiis .'.... 11 

Sambucus 105 

Sand, Drifting I49 

— Ferruginous 251 

— Shifting. Effect '. 479 

Sand in horticulture 261 

Sanding of moor soil 256 

Sandstone, Humus 243 

Sapocarbol 760 

Saprophytism 12 

Satureja hortensis 74 

Saxifraga cermta 76 

Scab of edible roots 2,(^1-1^ 

— of grape-vines 596-98, 601 

Scarification wounds 776-81 

Schizomycetes 62 

Sciadopytis. Nanism 144 

Scion in grafting. Mutual influence of 

stock and 841-47 

Sclcrotinia Libertinia 28 

Scoroglia ■ . ■ ■ 53 

Scurvy, Bark 372 

— Deep, of potatoes 430 

— Knotted 3^7 

— Surface, of roots 367 

Scurvy diseases 3^7-7- 

— from marling 370 

— of edible roots 3(>7-7- 

— spots in trees 461 

Sea level. Effect of elevation above.. 72-86 

Sea water. Inundation 192 

Secca molle 202 

Secretions of the root body 139, 270 

Seduni acre 75 

— album 75 

— hexangulare 75 

Seed. Automatic regulation of depth of 

sowing 113 



Seed. Burning 186 

— Candying 226, 387 

— Change 39 

— Coating. See Candying. 

— Covering 109 

— Cracking, due to sunburn 647-48 

— Depth of sowing no, 113 

— Germination in ice 499 

— ■ Germination in the fruit 321 

— Hard shelled condition 115, 420 

— Heaving due to frost 536-37 

— Higher germinating power 125 

— Injury from self-heating 652-53 

— Mechanical treatment 106-7 

— - Over-fertilization 387-89 

— • Quality decisive in germination. .. in 

— Retention of germinating power.. .107 

— Soaking 106, 112, 157-58, 295 

— Souring 201-203 

— • Sterilization in beets 225 

— Swelling 106 

— Too deep sowing 106-20 

— Weakness due to age 108 

Seed, Dormant, Germination log 

Seed time. Effect of postponement. .639-41 
Seeding, Delayed 200-201 

Susceptibility to parasitic 

attack . 200-201 

— Too thick 147 

Seeds. Specific gravity 295 

Seeds, Hard, in the Leguminosae. .. .420-22 

Soaking in sulphuric acid 421 

— Weak. Behavior 295-96 

Selection, Artificial 665 

Self-heating. Injury to seed 652-53 

Self-preservation in the organism 6 

Self -purpose in the organism 6 

Self-sterility in fruit 291 

Senility. Degeneration ' 34 

Sepedoniuiii (chrysospermum ?) 204 

Scrch disease of sugar cane 85, 692-96 

Serum therapy 23 

Sewage 392 

Sewage disposal beds 364-67 

Attraction to crows 364 

Injury from coating with 

ooze and mud 366 

Rats as pests 264 

Sodium chlorid content ....750 

Sexual organs in Cryptogams 289 

Shade. Effect on amount of harvest.. 657 

— Effect on hops 283 

Shade trees in coffee plantations 657 

Shading 411, 657-62 

Shadow pictures due to excessive light. 673 

Sheath growth 92 

Shelling of the grape blossom 354-56 

Shikuyobyo of the mulberry 650 

Shoots. Dropping I34 

Shrivelling disease of the mulberry. .690-92 

of tea 692 

Silicates, Ferric 251 

SUpha atrata 364 

Silt. Covering of soil igi-94 

Silver-leaf 285-86 

Silver-leaf due to lack of calcium 286 



905 



Skin disease of hyacinths 451-53 

Slime 198 

Slime cork 279 

— exudation of trees 854-55 

Slope of the soil surface 86-120 

Slopes, Too steep 89-91 

Small fruits. Dropsy 335-38 

Smelters. Smoke 738, 740 

Smoke. Chemical composition 738-39 

— Gases 718-36, 884 

— Soil poisoning 722 

Smoke as cause of disease 49, 459 

— predisposition to disease. . . .722 

Smoke Commissions, Federal 744 

Smoke injuries, Acute 721 

Chronic 721 

■ Invisible 721 

Smoke injuries with calcium fertiliz- 
ation 722 

— production in smelting furnaces. . .738 
Smudges as protection against frost.... 628 
Snow covering 76, 634 

. as protection against frost 624 

Snow pressure 634-37 

Soaking of seed. Advisability 295 

Soda dust 743 

Sodium chlorid 266 

content of sewage disposal 

beds 750 

fertilization 193 

in waste water 748-51 

■ — fumes 742 

— nitrate. Sec Nitrate of soda. 

— sulfid 741 

Soil. Absorption due to chemico- 

physical processes 264-68 

— Acid content ^40-41 

— Aeration 241 

— Alkalinity 367 

— "Baking" 405 

— Breaking up 183 

— Chemical constitutio:i. Unfavor- 

able 264-407 

— Covering with silt 191-94 

— Crust formation no 

— Cultivation 183-84, 226, 234, 245 

— Feeding Cultures 142 

— Flocculency 193 

— Harrowing 184 

— Hoeing 184 

— Impoverishment 91, 238, 266 

due to fertilization 266 

— Increased density due to washing.. 748 

— Irrigation 182-83 

— Lack of moisture 182 

— Leaching 243 

— Mechanical resistance 141 

— Mulching 184-85 

— Physical constitution, Unfavor- 

able 138-263 

— Poisoning 266 

from metallic sulfur 250-51 

from smoke 722 

— Pulverization 191 

— Reduction 190 

— Removal of turf 184 



Soil. Shading due to weeds 658 

— Slope of the surface 72, 86-91 

— Use of a plant cover 185-86 

Soil, Alkali 195, 267 

— Compact. Improvement 194-95 

— Dry. Suitable fruit varieties. .. 174-75 

— Favorable for Cassava 232 

for sweet potatoes 232 

for Taro 232 

for yams 232 

— Heavy. Overcoming dis- 

advantages of 232-40 

— Lean 152 

— Light 148-89 

— Loamy 189-240 

— Marshy, causing root decay .196 

— Moor. See Moor soil. 

— Peaty 185 

— Sandy. Capacity for becoming wet 

with dew 149 

Danger from frost i-;9 

Disadvantages 148-50 

Leaching 149, 243 

— Unfavorable for cocoa 230 

for coffee 230 

for cotton 229 

for maise 231 

for millet 232 

■ for Pennisefuin sficatuin 232 

for Sorghum 231 

for sugar 227 

for tea 23 1 

for tobacco 229-30 

for tropical plants 227, 232 

— Unripe 272 

— Virgin. ^Mosaic disease less pre- 
valent on 687 

Soil bacteria 256, 269 

— • conditions causing disease 72-407 

— encrustation 134, 405 

— exhaustion 265, 271 

— heat. Influence of excessive. 73, 648-50 

— in po-t cultures 140 

— mass. Limited T38-47 

— organisms. Work 268-74 

— ripening 273 

— • solution. Effect of too high con- 
centration 387 

— structure. Relation of food sub- 

stances 264-74 

Unsuitable 148-240 

— surface. Mulching 235 

Slope 86-120 

— warmth. See Soil heat. 

SoUdago virga aurca 84 

Soot. Composition 738 

— Injuriousness 737 

Sorghum. Unfavorable soil 231 

Sorghum millet. Mafitta disease 415 

Sorrel. Indication of scarcity of lime.. 237 

Souring of seed .201-203 

South wind. Destructive 636 

Specific gravity in seeds 295 

Specks, Brown, on foliage of potatoes. .297 

Sphacelus 608-13 

Sphaerocarpus 53 



90b 



Sphagnum 187, 249, 256 

— peat in horticulture 261 

Sphakelismos 42 

Spiloceae pomi Fr 168 

Spiiiacia oleracca 147 

Spiraea 105 

— Canker 598-600 

SpiraHsmus Mor 334 

Splitting of cucumbers 462 

Sporodesmium 710 

Spraying. Intumescence 441,762 

Spring growth. Freezing SS9-62 

— winds, Raw. Danger 479 

— wood 774 

Sprouting of fruit 375 

— of the stock 376, 378, 785 

Spruce. Layering 253-54 

— Sinker formation 255 

— Stilt growth 92-94 

— Top blight 91 

— • Usefulness 253-56 

Stalks. Lodging 542 

Staminody 342 

Starch formation 299 

Statistics of plant diseases 71 

Statocytes 858, 859 

Stem browning of cotton 228 

Stercuin hirsutum. Willd 614 

Sterigiiiafocystis nigra. Lack of 

potassium 300 

Sterile-head condition due to frost . .542-47 

Sterility 289-92 

Sterility, Hereditary 291 

Sterility due to drought 290 

Stilbum 54 

Stilts. Growth 92-98 

Stilts on pines 94 

Stimuli, Traumatic 885 

Stock, Grafting. Dwarf 105 

Mutual influence of scion 

and 841-47 

Sprouting 376, 378, 785 

Yellowing 284 

Stone fruits. See Pomes. 

Stones in soil. Significance 236 

Stoniness of pears 170-74 

Storage of winter apples 323 

Strain wood 553 

Stratification 159, 107 

Straw. Excessive growth in grain 365 

— • Fertilization 269 

Street planting 153-55 

Streets. Asphalting 106 

Streptothrix species. Humus ferment- 
ing organisms 272 

Strophomania 334 

Stunting of plants 175-/7 

— of trees, due to wind action 474 

Substrata, Nutritive, for parasites 17 

Suckers 33i 

Suffocation due to lack of oxygen 313 

Sugar. Accumulation due to lack of 

light 668 

— Blocking due to lack of light 667 

Sugar beets. Root blight 220-26 

Sugar cane. Cobb's disease 696-97 

Diseases 227-28 



Sugar Cane. Dongkellansickte 228 

Effect of lack of calcium 304 

• Leaf spot disease 228 

— - — Powdery disease 696 

— ■ — Root rot 227-28 

Rusts 696 

Serch disease 692-96 

Suillus 53 

Sulfarin. EfYect of use 372 

Sulfate of iron 192 

Sulfid, HA'drogen 98, 741, 742 

— Iron 250 

— ■ Sodium 741 

Sulfur. Lack. Changes due to 312 

Sulfur, Metallic. Poisoning of the 

soil 250-51 

Sulfuric acid. Free 250, 881 

Sulfuric acid for soaking hard seeds... 421 

Sulfurous acid 718-24, 884 

Summer defoliation 347, 411, 661 

— drought. Effect 501 

— rust of hops 282 

Sun cracks 647-48 

Sunburn. Blisters 642 

— Failure of seeds 643 

— Injury to bark . 647 

— Injury to buds 645 

— Injury to grapes 646-47 

— • Seed cracking 647-48 

Sunburn in blossoms 645-46 

— in Clivia nobilis 643 

— in fruits 645-46 

— of leaves in nature 641-43 

— spots on conservatory plants. . .643-44 

Sunlight. Effect of increased intensity. 75 

Superphosphates 768 

Surface wounds 831 

Swamps. Conversion of land into. .. 196-98 

Sweet potatoes. Favorable soil 232 

Symbionts. Graft callus formation 887 

Svmbiosis, Antagonistic n 

'— • Mutualistic n 

Symphoria 105 

Symptomatics 7 

Syringa. Twisting I77 

Tasretes I47 

Tail-rot of beets 697 

Taiuarix gaUica. Wind bending 474 

Tan disease 209-19 

— — Apple 210-13 

■ Cherry 213-17 

Plum 218 

Tannic substances 151 

Taphrina. Fr 146, I79 

Tar coating. Injury 756 

— fumes 72,^-2S 

— vapor 727 

Taro. Favorable soil 232 

Taste, Watery, in fruit 2,23 

Taxiis haccaia 254 

Tea. Shrivelling disease 692 

— Unfavorable soil 231 

Tears, Frost, Internal 5^9 

Tears due to drought 568 

Tecoma radicans. Fasciation 334 

Temperature. Fluctuations 88,504,506 



907 



Temperature, Low. Life phenomena. 498-500 

Tension differences due to frost 514 

Teratology 7 

Tetranyclius telarius 412 

Thawing 506, 5 1 1 

— Rapid no, 511 

Therapy 7 

— Internal 23-25 

— Serum 23 

Thielaviopsis cthaceticus 694 

Thiopene 460 

Thorn formation 297-98 

Thread formation in the potato 161-63 

Thuja 144 

Thuja (Biota) orienfalis 105 

— obtusa. Dwarf growth 142 

— Occidentalis 105 

— plicata 105 

— IVan-eana 105 

Thujopsis 144 

Tilia : . . 94 

Tilia parvifoUa 616 

Tillage. Dependence on friability of 

the soil 194 

Tip blight 91, 154, 299 

from lack of moisture 189 

Tips, Double, in grapes 345 

Tipula siispecfa Rtzb 614 

Tobacco. Bosuch 685 

— Brindle 685 

— Bunt 685 

— Calico 685 

— Chlorosis 685 

— Effect of covering the soil with 

silt 194 

— Effect of potassium fertilization. . .405 

— Fdulc 685 

— Frenching disease 685 

— Gay head 229 

— Mai de mosaic o 685 

— Mai della holla 685 

— Manche 685 

— Mosaic disease 229, 684-89 

— Mosaikbctcgsegc 685 

— La Mosaique 685 

— Mongrel disease 685 

— Nielle 685 

— Peh-sem 685 

— Pocfih 685 

— Pox 689-90 

— Rost 685 

— Ronille blanche 685 

— Susceptibility due to excessive de- 

velopment 230 

— Unfavorable soil 229-30 

— White rust 690 

Tomatoes. Effect of hail 467 

Top. Drying 91 

Top blight of conifers J87-89 

— dressing. Effect of ammonia salts. 268 
Effect of Chile saltpeter 390 

Torula monilioides Cord 855 

Tracery, Rusty 432 

Tradescantia 29 

Tradescantia virginica. Effect of lack 

of oxygen 313 

Trametcs Pini (Brot.) 615 



Tree of life. Chinese 142 

Japanese 142 

Tree roots. Elevation 92-98 

Influence 658 

Tree seeds. Treatment 158-60 

Tree trunks with "handles" 848 

Trees. Autumnal coloration 280-81 

— Goitre gnarl 378-87 

— Scurvy spots 461 

— Slimy exudations 854-55 

— Stunting due to wind 474 

— Swelling of wood 461 

— Too deep planting 98-106 

Trees, Fatty, as electrical conductors. . .483 

— Forest. Branch blight SS8-59 

— Starchy, as electrical conductors. .483 
Trees in cities and towns. Injuries due 

to electricity 493 

Trichia 53 

Trifolium pratcnse 107 

Triticum 126 

Tropical plants 190 

Failure 84-86 

Soil conditions 227, 232 

Tropics. Effect on development of 

vegetables 639 

Trunks. Internal splitting 581-83 

— • Lichen covering 331 

Tuber ..53 

Tuber, Bark 861-71 

Tuber cuttings of caladiums 828 

of potatoes 828 

— gnarls 863, 865 

Primordia 217 

Tubercle disease of the rubber plant. 449-51 

Tubercularia 54 

Tubers, Secondary, in potatoes 163 

Tulipa 109 

Tulips. Falling 652 

Turf. Burning 186 

— Removal from soil 184 

Turgenia latifoUa 74 

Turgor, causing leaf fall 351 

Turpentine fumes, causing injury 757 

Tuv 760 

Twig abcission 357-6o 

— • disease 376 

Twigs. Dying 134 

— Susceptibility induced by frost.... 154 
Twisting, Compulsory 334 

— Spiral 177, 334 

Twisting of the branches 815-16 

Tylenchus dcvastatrix 767 

— hyacinthii Pr 327 

— sacchari Soltw 693 

Ulex cnropacus L 150 

Ulmin 241 

Union of parts. See Fasciation. 

LIredo 47 

Uredo Fictis Cast 710 

Ustilago 49 

Ustilago Arenac C. B 53 

— Hordei C. B 53 

Vaccinium 242 

J'aleriana Phn 75 



9o8 



Valsa Icucostouia 154, 554 

— oxystoma 153, 558 

— pnii'.astri Fr 558 

Vanda coenilea. Spot disease 263 

Vanilla. Grafting experiments 838 

V'ariegation 307, 677-84 

Varieties, Oecological 7^ 

Vegetables. Effect of tropical climate 

on growth 639 

— Over-fertilization 392-93 

— Poor development in tropics 639 

Veltlieimia glauca. Dying of the blos- 
soms 297 

Vermicularia 54 

Verticillinin rubcrriinuni 204 

— Sacchari 227 

Viburnum Opulns 105 

Vicia Faba 80, 100 

Vinegar made from wine. Use in gum- 

mosis 707 

Viola arvensis 74 

- — CHCullato 75 

— tricolor •. 76 

Virescence 341 

Virnlencc. Theor\' 14 

Virus 684 

— Mosaic disease 687 

— See also Enzjmes. 

Vitis. Bud cuttings 828 

— See also Grapes. 

Vitis vinifera. Discoloration 280 

Viviparity 378 

Volcanoes, Injuries due to 751 

Volutella 54 

Waste lime 415 

causing dry rot 195 

heart rot 195 

Waste salts 401 

Waste water 748-55 

containing barium ohlorid 752 

calcium chlorid 751-52 

cobalt 755 

iron sulfate 755 

magnesium chlorid 751-52 

nickel " 755 

sodium chlorid 748-51 

zinc sulfate 752-53 

Water. Discoloration from alder bogs. 251 

— Excess 319-360 

— Scarcity. Top blight 189 

Cause of dwarfing 145 

— Use as a protection against frost.. 626 

Water, Stagnant 19", I99 

Water core of the apple 286-87 

— ends in the potato 163 

— lime 399 

— shoots 331 

— sprouts ii^-2,2, 474 

Watering, Injudicious 206-208 

Weakness. Parasites 15 

Weather. Effect 21-22 

Wedge cells 329 

Weeds. Soil shading 658 

Wen 863 

— Formation on the apple 882 

Whip grafting 837 



White lead. Injury 756 

White-leaf condition 307, 883 

Wilt disease of cotton 229 

Wilting 276-~y 

— • due to frost 548-51 

to injudicious watering 206 

— of foliage of root plants 365 

Wind 471-79 

— Effect 22, 462, 471-79 

on cocoa 472 

— Injury to leaves 477 

— Pruning action 474 

— Stunting of trees 474 

Wind, as protection against frost 627 

— Forest protection against 136 

Wind-break 136, 471 

Wind-fall 471 

Winter frost 637 

— grain. Harrowing 236 

— lightning 486 

— moisture 189 

— seed. Harrowing 236 

— sunburn 648 

Witches brooms 146, 376 

Use of Chile saltpeter 391-92 

Wood. Swelling in tree 461 

Wood, Curly 859 

— Gnarly 859 

— Red ". 553 

Wood nbers. Spiral twisting due to 

constriction 817 

Woody plants. Discoloration 279-81 

Woolly streaks in apple cores 324-26 

Wound bark 792 

— gum 851-54 

— protection 850-51 

— stimulus 871, 88s, 886 

— wall. Mobile 836 

— wood 772, 792 

Wounds 772-880 

— Overgrowth 783-87 

Wounds, Cleft 831 

— Gnawed 782 

— Rubbing 782 

Wounds due to grafting 831 

— due to resin gathering 780 

— to the axial organs 772-80 

Xanthium 176 

Xantltoria parictiiia cushions 330 

Yams. Favorable soil 232 

Yellow-leaf condition 192, 196 

— due to excessive light 671 

Yellow sickness 307 

Yellow spots 434-35 

in Dracaena 435 

HI Pandanus javanicus 434 

Yellowing due to grafting stock 284 

Zeoliths 265 

Zinc 740, 752 

— blend 752 

— oxid 752 

— salts 752 

— sulfate in waste water 752-53 

Zinnia I47 



INDEX, Etc. 



MANUAL 



OF 



Plant Diseases 



BY 



PROF. DR. PAUL SORAUER 



Third Edition — Prof. Dr. Sorauer 

In Collaboration with 

Prof. Dr. G. Lindau And Dr. L. Reh 

Private Docent at the University Assistant in the Museum of Natural 

of Berlin History in Hamburg 



TRANSLATED BY FRANCES DORRANCE 



Volume I 
NON-PARASITIC DISEASES 

BY 

PROF. DR. PAUL SORAUER 

BERLIN 



WITH 208 ILLUSTRATIONS IN THE TEXT 



PART I. 



MANUAL 



OF 



Plant Diseases 



BY 



PROF. DR. PAUL SORAUER 



Third Edition—Prof. Dr. Sorauer 

In Collaboration with 

Prof. Dr. G. Lindau And Dr. L. Reh 

Private Decent at the University Assistant in the Museum of Natural History 

of Berlin in Hamburg 



TRANSLATED BY FRANCES DORRANGE 



Volume I 
NON.PARASITIG DISEASES 

BY 

PROF. DR. PAUL SORAUER 

BERLIN 



WITH 208 ILLUSTRATIONS IN THE TEXT 



PART X. 



MANUAL 



OF 



Plant Diseases 



BY 



PROF. DR. PAUL SORAUER 



Third Edition—Prof. Dr. Sorauer 



la Collaboration with 



Prof. Dr. G. Lindau And Dr. L. Reh 



Privata Docent at the Uaiversity 
of Berlin 



Aitittant in the Muieum of Natural Hiitory 
in Hamburg 



TRANSLATED BY FRANCES DORRANGE 



Volume I 
NON-PARASITIC DISEASES 

BY 

PROF. DR. PAUL SORAUER 

BERLIN 



WITH 208 ILLUSTRATIONS IN THE TEXT 



